Ch 3

Nucleus

-For cells, the control center is the gene containing nucleus. The nucleus contains the instructions needed to build nearly all the body's proteins. It also dictates the kinds and amounts of proteins that are built at any one time in response to signals acting on the cell -skeletal muscle cells, bone destruction cells, and liver cells are multinucleate (many nuclei) -all of our body cells have nuclei except for mature red blood cells which are called anucleate (without a nucleus).

Roles of Plasma Membrane Receptors

-A group of integral proteins that serve as binding sites are collectively known as membrane receptors. The roles include: contact signaling and chemical signaling -Contact signaling: Cells come together and touch in order to recognize one another. This is important for normal development and immunity -Chemical signaling: The process in which a ligand, the chemical messenger, binds a specific receptor and initiates a response. Ligands include most neurotransmitters, hormones, and pancrines. When a ligand binds to a membrane receptor, the receptor's structure changes, and cell proteins are altered in some way. -G protein-coupled receptors exert their effect indirectly through a G protein, a regulatory molecule that acts as a middleman or relay to activate (or inactivate) a membrane-bound enzyme or ion channel. This generates second messengers, which connect plasma membrane events to the internal metabolic machinery of the cell. -Two types of second messengers: Cyclic AMP and Ionic calcium -These second messengers both typically activate protein kinase enzymes

Cytoskeleton

-A network of fibers that holds the cell together, helps the cell to keep its shape, and aids in movement -It acts as a cell's bones, muscles and ligaments by supporting cellular structures and providing the machinery to generate cell movements -There are three types of rods in the skeleton: microfilaments, intermediate filaments, and microtubules (none are membrane covered) -Microfilaments are the thinnest of the three, and are made up of protein strands called actin. Microfilaments are involved in cell movement or changes in cell shape. Except in muscle cells, where microfilaments are abundant and stable, these filaments are constantly breaking down and reforming. As they breakdown and reform, these filaments change the cell's shape. -Intermediate filaments are tough, insoluble protein fibers. These filaments are made up of tetramer fibrils and have a diameter between microfilaments and microtubules. Intermediate filaments are the most stable and permanent of the cytoskeletal elements and strongly resist tension. They attach to desmosomes, and their main job is to act as internal cables to resist pulling forces exerted on the cell. -Microtubules have the largest diameter and are hollow tubes made of proteins called tubulin. Microtubules constantly disassemble and then reassemble. Microtubules determine the overall shape of the cell, as well as the distribution of cellular organelles. Mitochondria, lysosomes, and secretory vesicles attach to the microtubules and motor proteins (kinesins, dyneins, etc.) continually move and reposition the organelles along the microtubules

Tight junctions

-A series of integral protein molecules in the plasma membranes of adjacent cells fuse together like the zipper of a ziploc bag. This forms an impermeable junction that encircles the cell and separates one fluid-filled compartment from another -Tight junctions help prevent molecules from passing through the extracellular space between adjacent cells and restricts the movements of membrane proteins Example: Tight junctions between epithelial cells lining the digestive tract keep digestive enzymes and microorganisms in the intestine from seeping into the bloodstream

Chromatin

-A system of bumpy threads weaving through the nucleoplasm -made up of 30% dna, 60% globular histone proteins (package and regulate DNA), and 10% RNA chains -The fundamental units of chromatin are nucleosomes which consists of flattened disc-shaped cores of eight histone proteins connected like beads on a string by a DNA molecule. -Histones provide a physical means for packing the very long DNA molecules in a compact, orderly way, but they also play an important role in gene regulation -When a cell is preparing to divide, the chromatin threads coil and condense enormously to form short, barlike bodies called chromosomes

Endomembrane system

-A system of organelles (described above) that work together to (1) produce, degrade, and export biological molecules, and (2) degrade potentially harmful substances. -This system includes the ER, Golgi apparatus, secretory vesicles, and lysosomes, as well as the nuclear envelope which includes all of the membranous elements that are either structurally connected or arise via forming or fusing transport vesicles

Active transport

-Active transport requires transport proteins that combine specifically and reversibly with the transported substances. In facilitated diffusion, it's always going with the gradient because it's powered by kinetic energy, however, in active transport, solutes and ions are moved against the concentration gradient -Two types of active transport: primary and secondary -In primary active transport, energy to do work comes directly from the hydrolysis of ATP by transport proteins called pumps where the transport protein is energized by the transfer of a phosphate group from ATP -In secondary active transport, transport is driven by energy stored in concentration gradients of ions created by primary active transport pumps. This form of transport always moves more than one substance at a time using a cotransport protein -Active transport only transports specific substances

How does resting potential come about

-Diffusion causes ionic imbalances that polarize the membrane, and active transport processes maintain that membrane potential -The resting membrane potential is determined mainly by the concentration gradient of potassium ions. This is due to the fact that at rest, the membrane is much more permeable to potassium ions than sodium ions. -A negative membrane potential (-90 mV) is established when the movement of potassium ions out of the cell equals potassium movement into the cell. At this point, the concentration gradient promoting potassium ions exiting exactly opposes the electrical gradient for potassium ion entry

Osmosis

-Diffusion of a solvent, such as water, through a selectively permeable membrane -Osmosis is important in determining the distribution of water in the various fluid-containing compartments of the body (cells, blood, etc.) -Even though water is highly polar, a small amount of it can sneak through the plasma membrane by osmosis because of its small size. Water moves freely and reversibly through water-specific channels called aquaporins, which allow single-file diffusion of water molecules. These are abundant in blood cells and in cells involved in water balance e.g. kidney tubule cells -Osmosis occurs when the water concentration differs on the two sides of a membrane. If the solute concentration on the two sides differ so does the water concentration. Higher solute concentration = Lower water concentration -The total concentration of all solute particles in a solution is referred to as the osmolarity of the solution. Equilibrium is reached when the water and solute concentration on both sides of a permeable membrane is the same -The higher the amount of nondiffusible, or nonpenetrating, solutes in a cell, the higher the osmotic pressure and the greater the hydrostatic pressure must be to resist further net water entry. In a plant cell: Hydrostatic pressure = push out; Osmotic pressure = suck in. -In living animal cells, since there's no rigid cell wall. Osmotic imbalances cause the animal cell to swell or shrink until (1) the solute concentration is the same on both sides of the membrane, or (2) the membrane stretches to its breaking point

Rough ER

-ER that is dotted with ribosomes -Proteins that are assembled on the ribosomes are enclosed in vesicles sent to the Golgi apparatus in order to undergo further processing -Functions: *the ribosomes manufacture all proteins secreted from cells, for this reason, the rough ER is abundant and well developed in most secretory cells, antibody-producing immune cells, and liver cells, which produce most blood proteins *The rough ER is the cell's membrane factory where integral proteins and phospholipids that form part of all cellular membranes are manufactured.

Endocytosis

-Endocytosis begins with a coated pit or infolding of the membrane which have a protein coating on the cytoplasmic face that deforms the membrane to produce the vesicle. -3 types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis -Phagocytosis: The cell engulfs some relatively large or solid material, such as a clump of bacteria, cell debris, or inanimate particles. When a particle binds to receptors on the cell's surface, cytoplasmic extensions called pseudopods form and flow around the particle. This forms an endocytotic vesicle called a phagosome which fuses with a lysosome and its contents are digested. -Pinocytosis: A bit of infolding plasma membrane surrounds a very small volume of extracellular fluid containing dissolved molecules. This droplet enters the cell and fuses with a sorting vesicle called an endosome. Pinocytosis is a routine activity of cells allowing them a way of sampling extracellular fluid. It is important for cells that absorb nutrients like cells that line intestines. -Receptor-mediated endocytosis: The main mechanism for specific endocytosis and transcytosis. This selective mechanism allows cells to concentrate material that is present only in small amounts in the extracellular fluid. The receptors for this process are membrane proteins that only bind to certain substances. Substances taken up by this mechanism include enzymes, insulin, low-density lipoproteins, and iron, but not pathogens.

What are the major classes of extracellular materials

-Extracellular fluid which includes interstitial fluid, blood plasma, and cerebrospinal fluid. ECF fluid dissolves and transports substances in the body. Interstitial fluid is the fluid in tissues that bathes all of our cells. To remain healthy, each cell must extract from the interstitial fluid the exact amount of substances it needs -Cellular secretions. These secretions include substances that aid in digestion and some that act as lubricants (saliva, mucus, serous fluids) -Extracellular mix. Thus is the most abundant extracellular material. Body cells are in contact with a jellylike substance composed of proteins and polysaccharides which serve as a "cell glue" that binds body cells together

Desmosomes

-These junctions serve as anchoring junctions. They are mechanical coupling scattered like rivets along the side of adjacent cells to prevent their separation -These junctions bind adjacent cells together like molecular velcro in the intercellular (between cells) space -These junctions help keep cells from tearing apart

Facilitated diffusion

-For molecules unable to undergo simple diffusion, they instead move through the membrane through a passive transport process called facilitated diffusion in which the transported substance either (1) binds to carrier proteins in the membrane and is ferried across or (2) moves through water-filled channel proteins -Carrier-mediated facilitated diffusion: Carriers are transmembrane proteins that are specific for transporting certain polar molecules or classes of molecules, such as sugars and amino acids, that are too large to pass through membrane channels. The carrier protein changes shape to move the binding site from one face of the membrane to the other in order to envelop and release the transported substance. -Channel-mediated facilitated diffusion: Channels are transmembrane proteins that transport substances, usually ions or water through aqueous channels from one side of the membrane to the other. Channels are selective due to pore size and the charges of the amino acids lining the pore. *Leakage channels are always open and simply allow ions or water to move according to concentration gradients *Gated channels are controlled (opened or closed), usually by chemical/electrical signals *Substances moving through these channels are always moving down the gradient -In facilitated diffusion, there is a maximum rate of diffusion, while in simple diffusion there is no cap to the rate of diffusion.

Cell adhesion molecules (CAMs)

-Found on almost every cell in the body -Play key roles in embryonic development and wound repair (situations where cell mobility is important) and in immunity -These glycoproteins act as: 1. Molecular velcro that cells use to anchor themselves to molecules in the extracellular space 2. The "arms" that migrating cells use to haul themselves past one another 3. SOS signals sticking out from the blood vessel lining that rally protective white blood cells to a nearby infected or injured area 4. Mechanical sensors that transmit info about changes in the extracellular matrix into the cell, bringing about a variety of cellular responses such as cell migration, proliferation (growth by cell division), and specialization

Usually, Na+ and Cl− cannot cross the plasma membranes of cells. What would happen to a cell if it suddenly became permeable to both Na+ and Cl−?

-If a cell suddenly became permeable to both Na+ and Cl−, then these solutes have become penetrating solutes. As result, the nonpenetrating solutes inside the cell would no longer be balanced by nonpenetrating solutes outside the cell. The cell would swell (and possibly lyse) as Na+, Cl−, and water all move into the cell.

Vesicular transport

-In this type of transport, fluids containing large particles and macromolecules are transported across cellular membranes inside bubble-like, membranous sacs called vesicles. Vesicular transport moves substances into the cell (endocytosis) and out of the cell (exocytosis). Energized by ATP -Transcytosis moves substances into, across, and then out of the cell. Common in the endothelial cells lining blood vessels b/c it provides a quick means to get substances from the blood to the interstitial fluid -Vesicular trafficking moves substances from one area (or membranous organelle) in the cell to another.

Primary active transport

-Includes calcium, hydrogen, and sodium-potassium pumps -The most important pump is the sodium-potassium pump where for each molecule of ATP used, the sodium-potassium pump drives 3 sodium ions out of the cell and pumps two potassium ions back in. This results in the concentration of potassium ions inside the cell to be much higher than outside. Because sodium-potassium ions leak slowly, but continuously through leakage channels, this allows the pump almost continuously. -Uncharged solutes diffuse down their concentration gradients, but ions diffuse according to electrochemical gradients. The charged faces of the membrane can help or hinder diffusion of ions driven by a concentration gradient. The electrochemical gradients maintained by the sodium-potassium pump is crucial for cardiac, skeletal muscle, and neuron function

What determines whether a given substance can cross the plasma membrane

-Lipid solubility: The more lipid soluble, the more readily it will diffuse across -Size: The smaller the molecule, the more readily it will diffuse across -Molecules that aren't small enough or soluble enough can still diffuse across the membrane if they're assisted by a carrier molecule like an ion channel or transport protein.

Flagella

-Longer than cilia. The only flagellated cell in the human body is a sperm -Cilia propels other substances across a cell's surface, whereas a flagellum propels the cell itself

Lysosomes

-Membranous organelles containing digestive enzymes -Lysosomes are large and abundant in phagocytes, the cells that dispose of invading bacteria and cell debris. Lysosomal enzymes can digest almost all kinds of biological molecules and work best in acidic conditions

Peroixsomes

-Membranous sacs containing enzymes which include oxidases and catalases -Oxidases detoxify harmful substances and their most important function is to neutralize free radicals, which are highly reactive chemicals with unpaired electrons that can scramble the structure of biological molecules. Oxidases turn these free radicals into hydrogen peroxide (still dangerous), but catalases quickly converts it to water -Peroxisomes are abundant in liver and kidney cells which are active in detoxification and they play a role in energy metabolism by breaking down and synthesizing fatty acids

what are the 3 types of RNA that act together to carry out DNA's instructions for polypeptide synthesis

-Messenger RNA (mRNA), relatively long nucleotide strands; resembles "half-DNA"; mRNA carries the coded information to the cytoplasm, where protein synthesis occurs -Ribosomal RNA (rRNA), along with proteins, forms the ribosomes, which consist of two subunits (large and small); the two subunits combine to form functional ribosomes, which are the sites of protein synthesis -Transfer RNA (tRNA), small, roughly L-shaped molecules that ferry amino acids to the ribosomes. There they decode mRNA's message for amino acid sequence in the polypeptide to be built -rRNA and tRNA do not transport codes for synthesizing, they are the final products of genes that code for them. They act together to "Translate" the message carried by mRNA

Mitochondria

-Mitochondria are the power plants of a cell, providing most of its ATP supply -There are more mitochondria in cells that are more active e.g. you'll find an abundance of mitochondria in kidney and liver cells, but relatively few in inactive cells like lymphocytes -A mitochondrion has two membranes each with a general structure of the plasma membrane. Outer membrane is smooth and featureless, but the inner membrane folds inward, forming shelf like cristae that protrude into the matrix which is a gel-like substance within the mitochondrion -Teams of enzymes break down products of food fuels to water and carbon dioxide, as they're broken down, some of the energy released is captured and used to form ATP. This is called cellular respiration because it requires oxygen -Mitochondria contain their own DNA, RNA, ribosomes, and are able to reproduce themselves -It is believed that mitochondria arose from bacteria that invaded the ancestors of plants and animal cells

Exocytosis

-Process by which a cell releases large amounts of material -Also used to rebuild the cell membrane by fusing lipids and proteins removed through endocytosis back into the membrane, expanding the membrane

How does RNA differ from DNA

-RNA is single-stranded, and it has a the sugar ribose instead of deoxyribose, and the base uracil instead of thymine

Tonicity

-Refers to the ability of a solution to change the shape of cells by altering the cells' internal water volume 3 types: Isotonic, hypertonic, hypotonic -Isotonic: Cells exposed to isotonic solutions retain their normal shape, and exhibit no net loss or gain of water *Equal solute/water concentrations in and out of the cells -Hypertonic: Cells immerse in hypertonic solutions lose water and shrivel, or crenate *Higher concentration of solutes inside of the cell -Hypotonic: Cells placed in a hypotonic solution plump up rapidly as water rushes into them. Because it contains no solutes, water continues to enter cells until they finally burst, or lyse *Higher concentration of solutes outside of the cell

Ribosomes

-Small, dark-staining granules composed of proteins and a variety of RNAs called ribosomal RNAs. -Ribosomes are sites of protein synthesis -Two types of ribosomes divide the chore of protein synthesis: Free ribosomes and membrane-bound ribosomes -Free ribosomes: These float freely in the cytosol. They make soluble proteins that function in the cytosol, mitochondria, and some organelles -Membrane-bound ribosomes: These are attached to membranes forming a complex called the rough endoplasmic reticulum. They synthesize proteins destined for incorporation into cell membranes or lysosomes -Ribosomes can switch back and forth between these two functions, attaching to and detaching from the membranes of ER, according to the type of protein they are making at the time

passive transport

-Substances cross the membrane without any energy input from the cell -Uses kinetic energy -Substances move from high to low concentration (down their concentration gradient)

Golgi apparatus

-The Golgi apparatus consists of stacked and flattened membranous sacs, shaped like hollow dinner plates. The Golgi Apparatus is the principle "traffic director" for cellular proteins. -The major function is to modify, concentrate, and package the proteins and lipids made at the rough ER ***Proteins destined for export are packaged into secretory vesicles that migrate to the plasma membrane and dump their contents by exocytosis ***Proteins destined for membranes fuse with and are incorporated into those membranes ***Digestive enzymes are packaged into vesicles that end up becoming lysosomes or fuse w/ lysosomes

active transport

-The cell provides metabolic energy (ATP) needed to move substances across the membrane -Substances move from low to high concentration (against their concentration gradient)

What is the cytoplasm

-The cellular material between the plasma membrane and the nucleus, is the site of most cellular activities -The cytoplasm consists of the cytosol, organelles, and inclusions

What is the plasma membrane composed of

-The lipid bilayer of the membrane is constructed largely of phospholipids with smaller amounts of cholesterol -The membrane is composed of lipids, proteins, and carbohydrates -Lipids: *Phospholipids form the basic structure of the membrane *Hydrophobic tails prevent water-soluble substances from crossing, forming a boundary *Cholesterol stiffens the membrane *Cholesterol Further decreases water solubility of membrane -Proteins: *Determines what functions the membranes can perform *Proteins have many roles e.g., transport, communication (acting as receptors for signal molecules), and joining to each other to the extracellular matrix -Carbohydrates: *Act as identify molecules which allow cells to recognize "Who is who" e.g., during developing so cells can sort themselves into tissues and organs. Carbs also allow immune cells to recognize our own cells versus pathogens *Carbohydrates are only found on the outer surface of the membrane. Together, the carbohydrates on the outside of the cell form a coating called the glycocalyx. The glycocalyx provides identity molecules which are specific biological markers by which approaching cells recognize each other

What does the plasma membrane do

-The plasma membrane separates intracellular fluid within cells and the extracellular fluid outside cells. -Nearly all cellular organelles are enclosed in a membrane

Cell junctions

-The plasma membranes of adjacent cells are joined together by specialized cell junctions that allow neighboring cells to adhere and sometimes communicate -These junctions may aid or inhibit movement of molecules between or past cells and also serve to tie cells together -3 types: Tight junctions, Desmosomes, and Gap junctions

Smooth ER

-The smooth ER is continuous with the rough ER and consists of tubules arranged in a looping network. Its enzymes play no role in protein synthesis, rather, they catalyze reactions.

Gap junctions

-These junctions are a communicating type of junction between adjacent cells -At gap junctions the adjacent plasma membranes are very close, and the cells are connected by hollow cylinders called connexons -Different types of gap junctions are composed of different transmembrane proteins and they determine what can pass through them from one cell to its neighbor -Ions, simple sugars, and other small molecules pass through these water-filled channels -These junctions are present in electrically excitable tissues like the heart and smooth tissue

What are integral proteins

-These proteins are firmly inserted into the lipid bilayer -Some protrude from 1 membrane face only, but most are transmembrane proteins that span the entire membrane and protrude on both sides -All integral proteins have both hydrophobic and hydrophilic regions which allows them to interact with both the nonpolar lipid tails buried in the membrane and the water inside and outside the cell -Some transmembrane proteins are involved in transport, and form channels, or pores in which small, water-soluble molecules or ions can move through it, bypassing the lipid part of the membrane. Other transmembrane proteins act as carriers that bind to a substance and then move it through the membrane. Some transmembrane proteins are enzymes. Others are receptors for hormones or other chemical messengers and relay messages to the cell interior which is a process called signal transduction

What are peripheral proteins

-These proteins are not embedded in the lipid bilayer, instead, they are either attached loosely to integral proteins or have a hydrophobic region that anchors them into the membrane -These proteins include a network of filaments that help support the membrane from its cytoplasmic inside -Some of these proteins are enzymes, others are motor proteins which are involved in mechanical functions, such as changing cell shape during cell division and muscle contraction. Others link cells together

secondary active transport

-This form of transport does not directly use ATP, but rather uses the concentration gradient as its source of energy which is created by primary active transport, specifically, by the sodium-potassium pump. -By moving sodium across the membrane against its concentration gradient, the pump stores energy in the gradient. A substance that's pumped across a membrane can do work as it leaks back, propelled "downhill" along its concentration gradient Example: As a sodium ion moves back into the cell, other substances are dragged along or cotransported by the same protein. Because the energy for this type of transport is the concentration gradient, the sodium ion has to be pumped back out of the cell to maintain its concentration gradient

Endoplasmic Reticulum (ER)

-This is an extensive system of interconnected tubes and parallel sacs called cisterns -The ER is continuous with the outer nuclear membrane -There is Rough ER and Smooth ER

What is the cytosol

-This is the viscous, semitransparent fluid in which the other cytoplasmic elements are suspended.

How does active transport maintain membrane potential

-This requires that the rate of active transport of Sodium ions out of the cell is equal to, and depends on, the rate of sodium ion diffusion into the cell. If more sodium ions enter, more is pumped out. -The sodium-potassium pump maintains both the membrane potential (charge separation) and the osmotic balance

Microvilli

-Tiny, fingerlike extensions of the plasma membrane that project from an exposed cell surface. They increase the plasma membrane surface area and are most often found on the surface of absorptive cells like intestinal and kidney tubule cells. -The major function of microvilli is to increase the cell's surface area for absorption of substances.

Simple diffusion

-Unassisted diffusion of lipid-soluble or very small particles -In simple diffusion, substances diffuse directly through the lipid bilayer. Usually small nonpolar molecules like gases (oxygen or carbon dioxide), steroid hormones, or fatty acids

Cilia

-Whip-like, motile cellular extensions that are usually in large numbers, on the exposed surface of certain cells. Ciliary action moves substances in one direction across cell surfaces. Example: cilia that line the respiratory tract propel mucus laden with dust particles and bacteria upward away from the lungs -Formed by centrioles

In their resting state, plasma membranes of all body cells exhibit what

-a resting membrane potential which is a voltage that exists across a plasma membrane during the resting state of an excitable cell. This makes all cells electrically polarized. -This voltage (or charge separation) exists only at the membrane -All of the positive and negative charges in the cytoplasm added up would be neutral. Also, t he positive and negative charges in the extracellular fluid balance each other out exactly

symport vs antiport

-both are facilitated diffusion -symport = 2 substrates in the same direction (Na+/glucose) -antiport = 2 substrates in opposite direction (Na+/H+)

Centrosomes

-microtubules are anchored at one end in a region near the nucleus called the centrosome or cell center -The centrosome acts as a microtubule organizing center and is distinguished by centrioles which are small, barrel-shaped organelles oriented at range angles to each other. The centrosome is best known for generating microtubules and organizing the mitotic spindle in cell division. -Centrioles also form the bases of cilia and flagella

Microtubules (end of ch question)

-moves organelles within cell using motor proteins

What are extracellular materials

-substances contributing to body mass that are found outside the cells

A result of a selective permeable plasma membrane is what

-the generation of a membrane potential, or voltage, across the membrane -While all body cells have a membrane potential, it is especially important for nerve and muscle cells because they use changes in membrane potential as a form of communication -A voltage is electrical potential energy resulting from the separation of oppositely charged particles

Is the inside of the plasma membrane negative or positive relative to its outside in a polarized membrane of a resting cell? (end of ch questions)

In a polarized membrane of a resting cell, the inside is negative relative to its outside.

Polypeptide synthesis has two steps:

1) Transcription, in which DNA's info is encoded in mRNA 2) Translation, in which the info carried by mRNA is decoded and used to assemble polypeptides

The speed of diffusion is influenced by what 3 factors

1. Concentration: The greater the difference in concentration of the diffusing molecules or ions between the two areas, the more collisions occur and the faster the particles diffuse 2. Molecular size: Smaller molecules diffuse more rapidly 3. Temperature. Higher temperature (more kinetic energy) increases the speed of molecular movement and means more rapid diffusion

A human cell has three main parts

1. Plasma membrane: The outer boundary of the cell, which acts as a selectively permeable barrier 2. Cytoplasm: The intracellular fluid packed with organelles, small structures that perform specific cell functions 3. Nucleus: An organelle that controls cellular activities. Typically the nucleus lies near the cell's center

What are the three aspects of cell theory

1. The cell is the smallest unit of life 2. All organisms are made of one or more cells 3. Cells only arise from other cells

A single protein may perform a combination of these functions in the plasma membrane

1. Transport *A protein that spans the membrane can open a channel to allow passage for a specific solute *Some proteins hydrolyze ATP as an energy source to actively pump substances across the membrane 2. Receptors for signal transduction *A protein exposed to the outside of a cell may have a binding site that fits the shape of a specific chemical messenger e.g. a hormone *When bound, this can lead to a change in shape that initiates a chain of chemical reactions 3. Enzymatic activity *A protein may be an enzyme with its active site exposed to substances in the adjacent solution *A team of several enzymes may catalyze steps of a metabolic pathway 4. Cell-cell recognition *Some glycoproteins serve as identification tags that are recognized by other cells 5. Attachment to the cytoskeleton and extracellular matrix *Elements of the cytoskeleton (cell's internal framework) and the extracellular matrix, may anchor to membrane proteins *This helps maintain cell shape, fixes the location of certain membrane proteins, and plays a role in cell movement 6. Cell-to-cell joining *Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions *Some membrane proteins provide temporary binding sites that guide cell migration and other cell-to-cell interactions

Gene

A segment of DNA on a chromosome that codes for a specific trait or carries info for creating one polypeptide chain -Our genes consist of long sequences of DNA, only some of which code for protein. The coding regions are called exons. Exons are separated from each other by long intervening sequences called introns -Introns act as control elements and they can allow for making different, but related, proteins from one gene by omitting or including certain exons

There are two major means of active membrane transport

Active transport and vesicular transport

How is RNA formed

All types of RNA are formed on the DNA in the nucleus. The DNA helix separates and one of its strands serves as a template for synthesizing a complementary RNA strand. Once formed, the RNA molecule migrates into the cytoplasm and the DNA recoils back into its helical, inactive form

How are microtubules and microfilaments related functionally?

Both microfilaments and microtubules are involved in organelle movements within the cell and/or movements of the cell as a whole.

Mitochondria (end of ch question)

Contains its own DNA

What two cell junctions do the muscle cells of the heart have

Desmosomes (anchoring junctions) that secure cardiac cells together as the heart pumps, and gap junctions (communicating junctions) that allow ions to flow from cardiac cell to cardiac cell

What process establishes the resting membrane potential? (end of ch questions)

Diffusion of ions, mainly the diffusion of K+ from the cell through leakage channels, establishes the resting membrane potential.

summary of vesicular transport

Endocytosis Phagocytosis -Energy source: ATP -Description: *A large external particle (proteins, bacteria, dead cell debris) is surrounded by a pseudopod and becomes enclosed in a vesicle (phagosome) -Example: *Occurs primarily in phagocytes (some white blood cells and macrophages) Pinocytosis -Energy source: ATP -Description: *Plasma membrane sinks beneath an external fluid droplet containing small solutes. Membrane edges fuse, forming a fluid-filled vesicle -Example: *Occurs in most cells, important for taking in dissolved solutes by absorptive cells of the kidney and intestine Receptor-mediated endocytosis -Energy source: ATP -Description: *External substance binds to membrane receptors *Selective endocytosis and transcytosis -Example: *Means of intake of some hormones, cholesterol, iron, and most macromolecules Vesicular trafficking -Energy source: ATP -Description: *Vesicles pinch off from organelles and travel to other organelles to deliver their cargo -Example: *Intracellular trafficking between certain organelles, e.g., endoplasmic reticulum and Golgi apparatus Exocytosis -Energy source: ATP -Description: *Secretion or ejection of substances from a cell *The substance is enclosed in a membranous vesicle, which fuses with the plasma membrane and ruptures, releasing the substance to the exterior -Example: *Secretion of neurotransmitters, hormones, mucus, etc.

Golgi apparatus (end of ch question)

Has cis and trans faces

Smooth ER, Golgi apparatus, Rough ER (end of ch question)

Has cisterns

What are inclusions

Inclusions are an internal structure in the cell that's responsible for storing energy and acting as a building block. Aids in osmotic balance and can either be free or bound in reference to the cytoplasm.

What is a semi-permeable membrane

It allows some substances to pass through while excluding others

What are organelles

Organelles are the metabolic machinery of the cell. Each type of organelle carries out a specific function for the cell

What is the connection of phagocytic cells being gathered in the lungs, particularly of a smoke

Phagocytic cells engulf debris, and a smoker's lungs would be laden with carbon particles and other debris from smoking

summary of active transport

Primary active transport -Energy source: ATP -Description: *Transport of substances against a concentration (or electrochemical) gradient *A pump protein moves substances across the membrane *Directly uses energy of ATP hydrolysis -Example: *Ions Secondary active transport -Energy source: Ion concentration gradient maintained with ATP -Description: *Cotransport (coupled transport) of two solutes across the membrane *Energy is supplied by the concentration gradient created by primary active transport *Symporters move the transported substances in the same direction; antiporters move transported substances in opposite directions across the membrane -Example: *Movement of polar or charged solutes, e.g. amino acids (into cell by symporters); Ca2+, H+ (out of the cells via antiporters)

What are the three types of passive transport across the plasma membrane

Simple diffusion, facilitated diffusion, and osmosis

Smooth ER (end of ch question)

Site of steroid hormone synthesis

Summary Golgi apparatus

Structure -A stack of flattened membranes and associated vesicles close to the nucleus Functions -Packages, modifies, and segregates proteins for secretion from the cell or incorporation into the plasma membrane. Also involved in packaging lysosomal enzymes

Summary Microtubules

Structure -Cylindrical structures made of tubulin proteins Functions -Support the cell and give it shape. Involved in intracellular and cellular movements. Form centrioles and cilia and flagella, if present

Summary Ribosomes

Structure -Dense particles consisting of two subunits, each composed of ribosomal RNA and protein. Free or attached to rough ER Functions -The site of protein synthesis

Summary microfilaments

Structure -Fine filaments composed of the protein actin Functions -Involved in muscle contraction and other types of intracellular movement; help forms the cell's cytoskeleton

Summary nucleus

Structure -Largest organelle. Surrounded by the nuclear envelope; contains fluid nucleoplasm, nucleoli, and chromatin Functions -Control center of the cell; responsible for transmitting genetic info and providing the instructions for protein synthesis

Summary flagellum

Structure -Like a cilium, but longer; only example in humans is the sperm tail Functions -Propels the cell

Summary Lysosomes

Structure -Membranous sacs containing acid hydrolases Functions -Gets rid of useless, harmful, or dead cells -Helps digest food

Summary Peroxisomes

Structure -Membranous sacs containing catalase and oxidase enzymes Functions -The enzymes detoxify toxic substances. The most important enzyme, catalase, breaks down hydrogen peroxide

Summary rough ER

Structure -Membranous system enclosing a cavity, the cistern, and coiling through the cytoplasm. Externally studded with ribosomes Functions -Studded with ribosomes and it's involved with the production, folding, quality control, and export of some proteins.

Summary smooth ER

Structure -Membranous system of sacs and tubules; free of ribosomes Functions -Site of lipid and steroid (cholesterol) synthesis, lipid metabolism, drug detoxification, and Ca2+ storage

Summary centrioles

Structure -Paired cylindrical bodies, each composed of nine triplets of microtubules Functions -As part of the centrosome, organize the microtubule network. During mitosis (cell division), form the spindle and asters. As basal bodies, they also form the bases of cilia and flagella

Summary intermediate filaments

Structure -Protein fibers; composition varies Functions -The stable cytoskeletal elements; resist mechanical forces acting on the cell

Summary Mitochondria

Structure -Rodlike, double-membrane structures; inner membrane is folded into projections called cristae Functions -Site of ATP synthesis; powerhouse of the cell

Summary Microvilli

Structure -Tubular extensions of the plasma membrane; contain a bundle of actin filaments Functions -Increase surface area for absorption

Summary cilia

Structure -Short cell-surface projections, each cilium contains 9 pairs of microtubules surrounding a central pair Functions -Coordinated movement creates a unidirectional current that propels substances across cell surfaces

Summary inclusions

Structure -Varied; includes stored nutrients such as lipid droplets and glycogen granules, protein crystals, pigment granules Functions -Storage for nutrients, wastes, and cell products

lysosomes vs peroxisomes

The lysosomal enzymes digest foreign substances engulfed by the cell, nonuseful or deteriorating organelles, or even the cell itself to prevent the buildup of cellular debris. The enzymes in peroxisomes detoxify harmful chemicals and neutralize free radicals.

Diffusion

The movement of molecules or ions from an area where they are in higher concentration to an area where they are in lower concentration Movement from high to low concentration is also called movement down or along a concentration gradient The driving force for diffusion is kinetic energy

Basal bodies

centrioles forming the bases of cilia and flagella

What does a cell's shape reflect?

its function

Mitochondria (end of ch question)

major site of ATP synthesis

Osmolarity vs tonicity

osmolarity refers to the solution or solute concentration, tonicity refers to the effect on the cell

Substances move through the plasma membrane in two ways

passively or actively

Structures of the nucleus

the nuclear envelope (membrane), nucleoli, and chromatin -The nucleus is bounded by the nuclear envelope which is a double membrane separated by a fluid-filled space. The outer membrane is continuous with the rough ER of the cytoplasm and is studded with ribosomes. The inner membrane is lined by nuclear lamina, a network of lamins that maintains the shape of the nucleus and acts as a scaffold to organize DNA in the nucleus. The nuclear envelope is punctured by nuclear pores which form an aqueous transport channel and regulates the entry and exit of molecules into and out of the nucleus -Within the nucleus are nucleoli, dark-staining bodies where ribosomal subunits are assembled. Nucleoli are not membrane-bounded and there's typically one or two per nucleus. They make large amounts of tissue proteins.