BSC 187 Chapter 5, test 4

in eukaryotes, where is DNA and RNA located

DNA is transcribed to RNA inside the nucleus, but the RNA molecules carrying the genetic message travel from inside to outside the nucleus, where they instruct the synthesis of proteins.

________ provide the eukaryotic cell with most of its usable energy > are organelles that harness energy from chemical compounds such as sugars and convert it into ATP, which serves as the universal energy currency of the cell. > rod shaped > the site of cellular respiration, and the oxygen that you take in with each breath is used by this to produce ATP

Mitochondria

a structural layer external to the plasma membrane that helps maintain the shape and internal composition of the cell; present in plants, fungi, and bacteria

cell wall

a type of cellular compartment that takes up excess water and waste products from inside the cell and expels them into the external environment

contractile vacuoles

the contents of the cell other than the nucleus make up the :

cytoplasm

a cellular system that includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, the plasma membrane, and the vesicles that move between them > it is a series of interconnected membrane-bound compartments in eukaryotic cells

endomembrane system

the organelle involved in the synthesis of proteins and lipids > The outer membrane of the nuclear envelope is physically continuous with the:

endoplasmic reticumlum

The Golgi apparatus has three primary roles, what are they

(1) it further modifies proteins and lipids produced by the ER; (2) it acts as a sorting station as these proteins and lipids move to their final destinations; and (3) it is the site of synthesis of most of the cell's carbohydrates.

in addition to the organelles, plant cells have what

> have a cell wall outside the plasma membrane, vacuoles specialized for water uptake, and chloroplasts that convert energy of sunlight into chemical energy > have intercellular connections called plasmodesmata, channels that allow the passage of large molecules such as mRNA and proteins between neighboring cells.

what is the difference between the rough ER and the smooth ER

> the rough ER is associated with ribosomes. Many proteins, including those that are destined for secretion, are synthesized by ribosomes associated with the rough ER >> synthesizes transmembrane proteins, proteins that end up in the interior of organelles, and proteins destined for secretion. As a result, cells that secrete large quantities of protein have extensive rough ER > The smooth ER lacks ribosomes and is the primary site of lipid synthesis >> the site of fatty acid and phospholipid biosynthesis. Thus, this type of ER predominates in cells specialized for the production of lipids

how do eukaryotes and prokaryotes differ

> transcription and translation differs > difference in the types of lipids that make up cell membranes > cholesterol is present in mammals. cholesterol belongs to a group of chemical compounds known as sterols. >> In eukaryotes other than mammals, diverse sterols are synthesized and present in cell membranes. Most prokaryotes do not synthesize sterols, but some synthesize compounds called hopanoids > prokaryotes are small, typically just 1-2 micrometers in diameter or smaller. eukaryotic cells are commonly much larger, on the order of 10 times larger in diameter and 1000 times larger in volume.

why does turgor pressure build

>builds as a result of water moving by osmosis into cells surrounded by a cell wall >Turgor pressure develops because the cell wall resists being stretched and pushes back on the interior of the cell, just as a balloon pushes back on the air inside.

how do vesicles form

>form by budding off an organelle, taking with them a piece of the membrane and internal contents of the organelle from which they derive. >They then fuse with another organelle or the plasma membrane, re-forming a continuous membrane and unloading their contents.

Why is the endoplasmic reticulum important?

>produces and transports many of the proteins and lipids used inside and outside the cell, including all transmembrane proteins, as well as proteins destined for the Golgi apparatus, lysosomes, or export out of the cell. > also the site of production of most of the lipids that make up the various internal and external cell

what does the cell wall do

>structural supports and protects the cell >Because the cell wall is rigid and resists expansion, it allows pressure to build up when water enters a cell

what gets embedded in lysosomal membrane

>the Golgi apparatus sorts and delivers specialized proteins that become embedded in lysosomal membranes. >> These include proton pumps that keep the internal environment at an acidic pH of about 5, the optimal pH for the activity of the enzymes inside. >> Other proteins in the lysosomal membranes transport the breakdown products of macromolecules, such as amino acids and simple sugars, across the membrane to the cytosol for use by the cell.

How do organisms such as plants, fungi, and bacteria maintain cell size and shape?

A key feature of these organisms is the cell wall surrounding the plasma membrane

what does the cell theory state

All living things are made up of cells, cells are the basic units of structure and function in living things, new cells are produced from existing cells there is no life without cells, and the cell is the smallest unit of life

What do mitochondria and chloroplasts do?

Both of these organelles are specialized to harness energy for the cell. Interestingly, they are both semi-autonomous organelles that grow and multiply independently of the other membrane-bound compartments, and they contain their own circular genomes.

How does cholesterol affect fluidity?

Cholesterol increases or decreases membrane fluidity depending on the temperature. > Cholesterol molecules constrain fluidity of the membrane by packing closely to neighboring phospholipids > At low temps lipid bilayers solidify, and cholesterol helps to maintain fluidity by keeping phospholipids apart

how long does the net movement of water toward the side of the membrane with higher solute continue during osmosis

During osmosis, the net movement of water toward the side of the membrane with higher solute concentration continues until a concentration gradient no longer exists or until the movement is opposed by another force.

The organelle that modifies proteins and lipids produced by the endoplasmic reticulum and acts as a sorting station as they move to their final destinations. > the ______ __________ is often the next stop for vesicles that bud off the ER

Golgi apparatus

what is the difference between diffusion and facilitated diffusion

In the case of facilitated diffusion, the molecule moves through a membrane transporter, whereas in the case of simple diffusion, the molecule moves directly through the lipid bilayer.

why does the function of lysosomes underscore the importance of having separate compartments within the cell bounded by selectively permeable membranes

Lysosomal enzymes cannot function in the normal cellular environment, which has a pH of about 7, and many of a cell's enzymes and proteins would unfold and degrade if the entire cell were at the pH of the inside of a lysosome. By restricting the activity of these enzymes to the lysosome, the cell protects proteins and organelles in the cytosol from degradation.

are specialized vesicles derived from the Golgi apparatus that degrade damaged or unneeded macromolecules (such as proteins, nucleic acids, lipids, and complex carbohydrates) They are the vesicles that degrade macromolecules.

Lysosomes

> in prokaryotes, a cell structure with multiple loops formed from supercoils of DNA: > Prokaryotes do not have a nucleus—that is, there is no physical barrier separating the genetic material from the rest of the cell. Instead, the DNA is concentrated in a discrete region of the cell interior known as the:

Nucleoid

how are plasmids commonly transferred between bacteria

Plasmids are commonly transferred between bacteria through the action of threadlike structures known as pili (pilus) , which extend from one cell to another (Genes for antibiotic resistance are commonly transferred in this way, which accounts for the quick spread of antibiotic resistance among bacterial populations.)

cells can be divided into two classes based on the absence or presence of a nucleus. what are they?

Prokaryotes, including bacteria and archaeons, lack a nucleus; eukaryotes, including animals, plants, fungi, and protists, have a nucleus

what is the difference between secondary active transport and primary active transport

Secondary active transport uses the potential energy of an electrochemical gradient to drive the movement of molecules; by contrast, primary active transport uses the chemical energy of ATP directly.

how can molecules that can't move across the lipid bilayer move toward a region of lower concentration

Some molecules that cannot move across the lipid bilayer directly can move passively toward a region of lower concentration through protein transporters.

how do the enzymes get into lysosomes

The enzymes inside the lysosomes are synthesized in the RER, sorted in the Golgi apparatus, and then packaged into lysosomes.

why is it that the small size of prokaryotic cells makes sense

The small size of prokaryotic cells means that they have a relatively high ratio of surface area to volume, which makes sense for an organism that absorbs nutrients from the environment. In other words, a large amount of membrane surface area is available for absorption relative to the volume of the cell that it serves

how are vesicles the primary means by which proteins and lipids move through the golgi apparatus to their final destinations?

These vesicles transport proteins and lipids from the ER to the Golgi apparatus, and then between the various cisternae, and finally from the Golgi apparatus to the plasma membrane or other organelles.

While traffic usually travels from the ER to the Golgi apparatus, a small amount of traffic moves in the reverse direction, from the Golgi apparatus to the ER. why does this occur

This reverse pathway is important to retrieve proteins in the ER or Golgi that were accidentally moved forward and to recycle membrane components.

the "uphill" movement of substances against a concentration gradient requiring an input of energy.

active transport

Within cells, sodium is kept at concentrations much lower than in the exterior environment; the opposite is true of potassium. Therefore, both sodium and potassium have to be moved against a concentration gradient. The sodium-potassium pump actively moves sodium out of the cell and potassium into the cell. This movement of ions takes energy, which comes from the chemical energy stored in:

adenosine triphophate (ATP)

what does the structure of a cholesterol molecule allow

allows a cholesterol molecule to insert itself into the lipid bilayer so that its head group interacts with the hydrophilic head group of phospholipids, while the ring structure participates in van der waals interactions with the fatty acid chains

what does the nuclear membrane of eukaryotes allow for

allows for more complex regulation of gene expression than is possible in prokaryotic cells

what does the structure of transmembrane proteins allow

allows for separate functions and capabilities of each end of the protein. For example: the hydrophilic region on the external side of a receptor can interact with signaling molecules, whereas the hydrophilic region of that receptor protein on the internal side of the membrane often interacts with other proteins in the cytoplasm of the cell to pass along the message.

the physical separation by membranes of the endomembrane system allows for waht

allows specific functions to take place within the spaces defined by the membranes and within the membrane itself.

Proteins destined for mitochondria or chloroplasts often have a signal sequence at their:

amino ends

molecules with both hydrophilic and hydrophobic regions in a single molecule are termed:

amphipathic

a membrane protein that attaches to other proteins and helps to maintain cell structure and shape

anchors

from an evolutionary perspective, why are archaeons and eukaryotes are more closely related to each other than either is to bacteria

archaeons share with eukaryotes many genes involved in transcription and translation, and DNA is packaged with histones in both groups.

How do amphipathic molecules interact with water?

arrange themselves into various structures in which the polar head groups on the outside interact with water and the nonpolar tail groups come together on the inside away from water. This arrangement results from the tendency of polar molecules like water to exclude nonpolar molecules or nonpolar groups of molecules

some molecules diffuse freely across the plasma membrane, why?

as a result of differences in concentrations between the inside and the outside of a cell

why do lipids freely associate with one another

because of their extensive van der waals forces between their fatty acid tails these weak interactions are easily broken & reformed

a two layered structure of the cell membrane with hydrophilic "heads" pointing outward toward the aqueous environment and hydrophobic "tails" oriented inward away from water

bilayer

The movement of these vesicles from the ER to the Golgi apparatus and then to the rest of the cell is part of a ___________ _____________ in which lipids and proteins are sequentially modified and delivered to their final destinations.

biosynthetic pathway

what are the three similarities between mitochondria and chloroplasts

both are organelles involved in energy metabolism; they are descendants of free living bacteria; they are surrounded by a double membrane; and they contain circular genomes

how do Human red blood cells avoid shrinking or bursting

by maintaining an intracellular environment isotonic with the extracellular environment, meaning the blood.

how does water move in and out of the cell

by passive transport; water moves through the plasma membrane by protein channels called aquaporins

> binds to and then transports specific molecules.

carrier: the second type of membrane transporter

animals often maintain ______ _____ by using active transport to keep the inside and outside of the cell ________

cell size; isotonic

what are the 3 different ways in which cells maintains size and shape

cells maintain size and shape in 3 ways 1) cells can use active transport to maintain the intracellular solute concentration so that it equals the extracellular solute concentration 2) the cell walls of plants, fungi, and bacteria help maintain the cell's size and shape by providing a rigid structure surrounding the cell membrane 3) some single celled eukaryotes contain a contractile vacuole that takes up excess water inside the cell and expels it through contracting

two types of membrane transporters may be used. what are they

channel and carrier

> provides an opening between the inside and outside of the cell through which certain molecules can pass, depending on their shape and charge.

channel: the first type of membrane transporter

what do enzymes within the golgi apparatus do

chemically modify proteins and lipids as they pass through it > These modifications take place in a sequence of steps, each performed in a different region of the Golgi apparatus, because each region contains a different set of enzymes that catalyzes specific reactions

>The major photosynthetic pigment contained in the photosynthetic membrane system; it plays a key role in the cell's ability to capture energy from sunlight. > appears green because it is poor at absorbing green wavelengths. The green color explains why so many plants have green leaves

chlorophyll

Both animal and plant cells have mitochondria to provide them with life-sustaining ATP. In addition, plant cells and green algae have organelles called: that capture the energy of sunlight to synthesize simple sugars

chloroplasts

an organelle in photosynthetic eukaryotes that converts energy of sunlight into chemical energy by synthesizing simple sugars

chloroplasts

________________ is a major component of animal cell membranes, representing approximately 30% by mass of membrane lipids

cholesterol

The series of flattened membrane sacs that make up the Golgi apparatus, surrounded by many small vesicles

cisternae

What are transmembrane proteins composed of

composed of three regions: 2 hydrophilic regions, 1 protruding from each face of the membrane, and a connecting hydrophobic region that spans the membrane

the jelly-like internal environment of the cell that surround the organelles inside the plasma membrane is referred to as the:

cytosol

what does the degree of membrane fluidity depend on

depends on which types of lipid make up the membrane. the composition of cell membranes affects the tightness of packing. single layer of lipid bilayer: the strength of the van der waals interactions between the lipids' tails depends on the length of the fatty acid tails and the presence of double bonds between neighboring carbon atoms. The longer the fatty acid tails, the more surface is available to participate in van der waals interactions. the tighter packing that results tends to reduce lipid mobility

the random motion of molecules, with net movement occurring from areas of higher to lower concentration of the molecules

diffusion

Because protons carry a positive charge, the side of the membrane with more protons is more positive than the other side. This difference in charge is called an

electrical gradient

A gradient that has both charge and chemical components is known as an

electrochemical gradient

The process in which a vesicle buds off from the plasma membrane, bringing material from outside the cell into that vesicle, which can then fuse with other membranes.

endocytosis

a protein that functions as a catalyst to accelerate the rate of a chemical reaction; enzymes are critical in determining which chemical reactions take place in a cell

enzymes

The process in which a vesicle fuses with the plasma membrane and empties its contents into the extracellular space or delivers proteins to the plasma membrane.

exocytosis

When a molecule moves by diffusion through a membrane protein and bypasses the lipid bilayer, the process is called

facilitated diffusion

when describing membranes, the ability of membrane lipids to move in the plane of the membrane

fluid

a model that proposes that the lipid bilayer is a fluid structure that allows molecules to move laterally within the membrane and is a mosaic of two types of molecules, lipids, and proteins

fluid mosaic model

what are the two places proteins are produced

free ribosomes in the cytosol and membrane-bound ribosomes on the rough ER

the __________with which molecules collide has important consequences for chemical reactions, which depend on the _________ of molecules

frequency; interaction

the nucleus houses the _____ and is the site of _______ synthesis

genone; RNA

The active regulation and maintenance, in organisms, organs, or cells, of a stable internal physiological state in the face of a changing external environment.

homeostasis

In the absence of the sodium-potassium pump, the extracellular solution becomes hypotonic relative to the inside of the cell. Poisons such as the snake venom ouabain can interfere with the action of the sodium-potassium pump. What are the consequences for the cell?

if the sodium patassium pump is made inactive, the cell will swell and even burst, as the intracellullar fluid becomes hypertonic relative to the outside of the cell and water moves into the cell by osmosis

where do proteins with no signal sequence remain

in the cytosol

A protein that is permanently associated with the cell membrane and cannot be separated from the membrane experimentally without destroying the membrane itself.

integral membrane proteins

The various membrane proteins can be classified into two groups depending on how they associate with the membrane. what are they

integral membrane proteins and peripheral membrane proteins

Proteins targeted to the nucleus usually have signal sequences located:

internally

protein channels and transporters in the membrane can greatly facilitate the movement of molecules, including

ions, water, and nutrients, that cannot cross the lipid bilayer on their own

why is the plasma membrane important

is not simply a passive boundary or wall. The environment outside the cell is constantly changing. In contrast, the internal environment of a cell operates within a narrow window of conditions, such as a particular pH range or salt concentration. It is the plasma membrane that actively maintains intracellular conditions compatible with life.

does cholesterol decrease or increase fluidity at the temperatures typically found in a cell

it decreases membrane fluidity because the interaction of the rigid ring structure of cholesterol with the phospholipid fatty acid tails reduces the mobility of the phospholipids Thus it helps maintain a consistent state of membrane fluidity by preventing dramatic transitions from a fluid to a solid state

what does diffusion lead to

leads to a net movement of the substance from one region to another when there is a concentration gradient in the distribution of a molecule, meaning that there are areas of higher and lower concentrations. When there is no longer a concentration gradient, net movement stops but movement of molecules in both directions continues.

Although lipids are free to move in the plane of the membrane, the spontaneous transfer of a lipid between layers of the bilayer, known as:

lipid flip flop

lipids assembled in a defined patch in the cell membrane

lipid rafts

- main component of cell membranes - have properties that allow them to form a barrier in an aqueous (watery) environment

lipids

What are the roles of lipids and proteins in maintaining the selective permeability of membranes?

lipids help maintain the selective permeability of the membrane by preventing charged molecules and ions from diffusing freely into the cell. They also allow molecules such as gases and small polar molecules to diffuse freely through the membrane. molecules such as proteins and polysaccharides are too large to cross the plasma membrane without help. Proteins in the membrane help transport these larger molecules by acting as channels and carreirs that transport molecules into and out of the cell. Each kind of channel or carrier is specific for one or a few molecules

an enclosed bilayer structure spontaneously formed by phospholipids in environments with neutral pH, like water

liposomes

In eukaryotes, the continuous interior of the endoplasmic reticulum; in plants, a fluid-filled compartment enclosed by the thylakoid membrane; generally, the interior of any tubelike structure.

lumen

In contrast to proteins synthesized by free ribosomes, proteins produced on the rough ER end up in the:

lumen of the endomembrane system, secreted out of the cell, or as transmembrane proteins

lysosomes degrade ________

macromolecules

a spherical structure in which lipids with bulky heads and a single hydrophobic fatty acid tail are packed

micelles

the membranes of two organelles, ________ and _______ are not part of the endomembrane system

mitochondria and chloroplasts

are mitochondria present in animal cells, plant cells, or both?

mitochondria are present in both animal and plant cells

the golgi apparatus ________ and _______ proteins and lipids

modifies; sorts

the cell structure, composed of two membranes, inner and outer, that defines the boundary of the nucleus (each is a lipid bilayer with associated proteins)

nuclear envelope

The signal sequence for the nucleus that enables proteins to move through pores in the nuclear envelope > enables proteins to move through pores in the nuclear envelope

nuclear localization

One of many protein channels in the nuclear envelope that act as gateways that allow molecules to move into and out of the nucleus and are thus essential for the nucleus to communicate with the rest of the cell The inner and outer membranes are continuous with each other at openings called:

nuclear pores

a compartment of the cell that houses the DNA in chromosomes

nucleus

most phospholipids are made up of what

of a glycerol backbone attached to a phosphate group and two fatty acids

Because many types of molecules are unable to cross cell membranes on their own, the endomembrane system divides the interior of a cell into two distinct "worlds,". what are they

one inside the spaces defined by these membranes and one outside these spaces.

membrane carriers exist in 2 conformations:

one that is open to one side of the cell, and another that is open to the other side of the cell. Binding of the transported molecule induces a conformational change in the membrane protein, allowing the molecule to be transported across the lipid bilayer

when does passive transport work in the cells advantage

only if the concentration gradient is in the right direction, from higher on the outside to lower on the inside for nutrients that the cell needs to take in, and from higher on the inside and lower on the outside for wastes that the cell needs to export

any one of several compartments in eukaryotes that divide the cell contents into smaller spaces specialized for different functions

organelles

The net movement of a solvent such as water across a selectively permeable membrane such as the plasma membrane is known as:

osmosis

the pressure needed to prevent water from moving from one solution into another by osmosis

osmotic pressure, it is a way of describing the tendency of a solution to "draw water in" by osmosis

What is the difference between passive and active transport?

passive transport into and out of cells work through diffusion (the random movement of molecules) when there is a concentration difference (concentration gradient) of a particular molecule across the cell membrane, the molecule moves from the area of higher concentration to the area of lower concentration. When a molecule cannot move across the plasma membrane on its own, it is sometimes able to passively diffuse through channels or carriers in the lipid bilayer, in a process called facilitated diffusion. In contrast, the active transport is used to move a molecule into or out of the cell against its concentration gradient. Molecules move through transport proteins embedded in the cell membrane. This type of transport requires energy, either directly (primary active transport) or indirectly ( secondary active transport)

the simplest form of movement into and out of cells is: it works by:

passive transport; diffusion

> can be associated with either the internal or external side of the membrane > these proteins interact either with the polar heads of lipids or with integral membrane proteins by weak noncovalent interactions such as hdydrogen bonds > only transiently associated w the membrane and can play a role in transmitting information received from external signals > can limit the ability of transmembrane proteins to move within the membrane and assist proteins in clustering in lipid rafts

peripheral membrane proteins

A protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions. they are easily separated from the membrane by simple experimental procedures that leave the structure of the membrane intact

peripheral membrane proteins

what are the major types of lipids found in cell membranes

phospholipids

> The biochemical process in which carbohydrates are built from carbon dioxide and water using the energy of sunlight. > results in the release of oxygen as a waste product

photosynthesis

what do membranes do

physically separate cells from their external environment and define spaces within many cells that allow them to carry out their diverse functions

the membrane that surrounds the cytoplasm of the cell, separating the inside of the cell from the outside of the cell; also called the cell membrane

plasma membrane

> In bacteria, a small circular molecule of DNA carrying a small number of genes that replicate independently of the DNA in the bacterium's circular chromosome. > Bacteria often contain additional small circular molecules of DNA known as __________ that carry a few genes.

plasmids

active transport that uses the energy of ATP directly

primary active transport

membrane protein that uses the energy stored in ATP to move sodium and potassium ions against their concentration gradients

primary active transport

the process by which proteins end up where they need to be to perform their function Directs proteins in the cytosol, the lumen of organelles, or the membranes of the endomembrane system, or even out of the cell entirely

protein sorting

the endoplasmic reticulum is involved in _____ and ______ synthesis

protein; lipid

most membranes contain _______ which represent as much as 50% by mass of the membrane of a red blood cell

proteins

How does a protein end up free in the cytosol, embedded in the plasma membrane, or secreted from the cell?

proteins produced on free ribosomes in the cytosol are directed to their final destination through particular amino acid sequences called signal sequences. these proteins are sorted after they have been translated. Proteins destined for the nucleus, mitochondria, and chloroplasts have specific signal sequences (e.g., nuclear localization signals will direct the protein to the nucleus). Proteins with no signal sequence remain in the cytosol. Proteins produced by ribosomes on the rough endoplasmic reticulum end up in the lumen of the endomembrane system or embedded in its membrane. They may also be secreted out of the cell. these proteins are sorted as they are translated. they are initially translated by a ribosome in the cytosol, but a signal sequence in the growing protein directs the ribosome to a channel on the rough ER. as the protein is translated, it is threaded through the channel. these proteins are destined for the ER lumen, Golgi apparatus, lysosomes, or for secretion outside the cell. If the protein contains an additional signal sequence called a signal anchor sequence, it remains in the ER membrane as it is synthesized, rather than passing entirely into the ER lumen.

a molecule on cell membranes that detects critical features of the environment. ________ detecting signals that easily cross the cell membrane are sometimes found in the cytoplasm

receptors

A complex structure of RNA and protein, bound to the cytosolic face of the RER in the cytoplasm, on which proteins are synthesized. > ____________ are the sites of protein synthesis, in which amino acids are assembled into polypeptides guided by the information stored in mRNA

ribosomes

How do saturated and unsaturated fatty acids differ?

saturated fatty acid tails, which have no double bonds, are straight and tightly packed - reducing mobility. the double bonds in unsaturated fatty acids introduce kinks in the fatty acid tails, reducing the tightness of packing and enhancing lipid mobility in the membrane

Protons are pumped across a membrane by (a) primary active transport, resulting in (b) an electrochemical gradient, which drives (c) the movement of another molecule against its concentration gradient.

secondary active transport

The movement of protons is always from regions of higher to lower concentration, whereas the movement of the coupled molecule is from regions of lower to higher concentration. Because the movement of the coupled molecule is driven by the movement of protons and not by ATP directly, this form of transport is called

secondary active transport

describes the properties of some membranes, including the plasma membrane, which lets some molecules in and out freely, lets others in and out only under certain conditions, and prevents other molecules from passing through at all

selectively permeable

An RNA-protein complex that binds with part of a polypeptide chain and marks the molecule for incorporation into the endoplasmic reticulum (eukaryotes) or the plasma membrane (prokaryotes).

signal recognition particle (SRP)

Proteins produced on free ribosomes are sorted after they are translated. These proteins often contain amino acid sequences, called _______ _______, that allow them to be recognized and sorted

signal sequences

an amino acid sequence that directs a protein to its proper cellular compartment

signal sequences

In protein sorting, an amino acid sequence in a polypeptide chain that embeds the chain in the membrane > Proteins destined for cell membranes contain a _____________ ___________ in addition to the amino-terminal signal sequence

signal-anchor sequence

what does the nucleus store

stores DNA, the genetic material that encodes the information for all the activities and structures of the cell

what is cholesterol composed of

the hydrophilic region is a hydroxyl group (-OH) and the hydrophobic region consists of four interconnected carbon rings with an attached hydrocarbon chain

what are the names and functions of the major organelles of the endomembrane system in eukaryotic cells

the nucleus stores the cell's genetic information and is the site of transcription. the endoplasmic reticulum (ER) is the organelle in which proteins and lipids are synthesized. the golgi apparatus modifies proteins and lipids produced by the ER and acts as a sorting station as those molecules move to their final destinations. Lysosomes contain enzymes that break down macromolecules such as proteins, nucleic acids, lipids, and complex carbohydrates

why is pH important in lipids

the pH is important because it ensures that the head groups are in their ionized (charged) form and suitable hydrophilic

Which part of a phospholipid is hydrophobic and hydrophilic?

the phosphate head group is hydrophilic because it is polar, enabling it to form hydrogen bonds with water. the two fatty acid tails are hydrophobic because they are nonpolar and do not form hydrogen bonds with water

what does the presence of a nucleus in eukaryotes allow for

the processes of transcription and translation to be separated in time and space. This separation, in turn, allows for more complex ways to regulate gene expression than are possible in prokaryotes

what is the result of the membrane's ability to act as a selective barrier

the result of the combination of lipids and embedded proteins of which it is composed. The hydrophobic interior of the lipid bilayer prevents ions and charged polar molecules from moving across it

why are membranes considered dynamic

they are continually moving, forming, and reforming during the lifetime of a cell

A highly folded membrane in the center of the chloroplast that contains light-collecting pigments and that is the site of the photosynthetic electron transport chain.

thylakoid

proteins that span the entire lipid bilayer; most integral membrane proteins are ___________________

transmembrane proteins

membrane proteins that move ions or other molecules across the cell membrane

transporters

membrane proteins serve different functions like

transporters, receptors, enzymes, anchors

The force exerted by water pressing against an object is called:

turgor pressure

cell membranes are composed of how many layers of lipids

two

A membrane-bound organelle present in some cells, including plant and fungal cells, that contains fluid, ions, and other molecules; in some cases, it absorbs water and contributes to turgor pressure.

vacuole

in eukaryotic cells, the membranes of organelles are either physically connected by membrane "bridges" or transiently connected by _________, small membrane enclosed sacs that transport substances within a cell or from the interior to the exterior of the cell

vesicles

If a red blood cell is placed in a hypertonic solution (one with a higher solute concentration than that inside the cell), what happens

water leaves the cell by osmosis and the cell shrinks

A container is divided into two compartments by a membrane that is fully permeable to water and small ions. Water is added to one side of the membrane (side A), and a 5% solution of sodium chloride (NaCl) is added to the other (side B). In which direction will water molecules move? In which direction will sodium and chloride ions move? When the concentration is equal on both sides, will diffusion stop?

water molecules move in both directions, but the NET movement of water molecules is from side A to side B. Water moves from regions of higher water concentration to regions of lower water concentration. Likewise, sodium and chloride ions move in both directions, but the NET movement of sodium and chloride ions is from side B to side A. Movement of water and ions results from diffusion, the random motion of substances. Even when the concentrations of all molecules are the same on the two sides, diffusion still occurs, but there is no net movement of water molecules or ions

if a red blood cell is placed in a hypotonic solution (one with a lower solute concentration than that inside the cell), what happens

water moves into the cell by osmosis and the cell lyses, or bursts.