chapter 6, the cell

Cell Theory

"The theory that all living things are made of cells, that cells are the basic units of organisms, and that cells come only from existing cells"

ribosomes

"packets" of RNA that are the site of protein synthesis the eukaryotic cells genetic instructions are housed in the nucleus and carried out by ribosomes They are protein structures that synthesize proteins from amino acids. The are found both free-floating in the cytoplasm of cells and also attached to the Rough Endoplasmic Reticulum. Wherever they're found, their purpose is the same: make proteins. They take "instructions," found in mRNA, and translate them into the amino acid sequence of a protein. ribosomes are not membrane bounded and thus are not considered organelles Cells that have high rates of protein synthesis have particularly large numbers of ribosomes Types of ribosomes: Free ribosomes-suspended in cytosol synthesize proteins that function within cytosol Bound ribosomes: attached to outside of endoplasmic reticulum, synthesize proteins for export or for membranes ribosomes can alternate between the two roles. Most of the proteins made on free ribosomes function within the cytosol.

scanning electron microscope (SEM)

especially useful for detailed study of the topography of a specimen

electron microscope (EM)

focuses a beam of electrons through the specimen or onto its surface Resolution is inversely related to the wavelength of the light (or electrons) a microscope uses for imaging, and electron beams have much shorter wavelengths than visible light. Modern electron microscopes can theoretically achieve a resolution of about 0.002 nm, though in practice they usually cannot resolve structures smaller than about 2 nm across

lysosome

helps break down food/worn out parts A lysosome is a membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest macromolecules. enzymes & membrane of lysosomes are synthesized by rough ER & transferred to the Golgi a little "stomach" for the cell also the "clean up crew" of the cell Lysosomes fuse with food vacuoles.....Polymers are digested into monomers Lysosomes also use their hydrolytic enzymes to recycle the cell's own organic material, a process called autophagy. During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane and a lysosome fuses with the outer membrane of this vesicle The lysosomal enzymes dismantle the enclosed material, and the resulting small organic compounds are released to the cytosol for reuse. With the help of lysosomes, the cell continually renews itself. A human liver cell, for example, recycles half of its macromolecules each week.

cytoskeleton

a microscopic network of protein filaments and tubules in the cytoplasm of many living cells, giving them shape and structure Roles of the Cytoskeleton: Support and Motility/ Shape This is especially important for animal cells, which lack walls. The remarkable strength and resilience of the cytoskeleton as a whole are based on its architecture. Like a dome tent, the cytoskeleton is stabilized by a balance between opposing forces exerted by its elements. And just as the skeleton of an animal helps fix the positions of other body parts.The cytoskeleton is more dynamic than an animal skeleton, however. It can be quickly dismantled in one part of the cell and reassembled in a new location, changing the shape of the cell. the cytoskeleton provides anchorage for many organelles and even cytosolic enzyme molecules Proteins that make up the fibers are very similar in all living things. from bacteria to humans....tubulin (all cells) and actin (eukaryote cells)..... Means that they are both are ancient and essential to life 3 main protein fibers: microtubules, microfilaments and intermediate filaments.

nuclear envelope

A double membrane that surrounds the nucleus in the cell. Controls what enters/exits nucleus The nuclear envelope is a double membrane. The two membranes, each a lipid bilayer with associated proteins, are separated by a space of 20-40 nm. The envelope is perforated by pore structures that are about 100 nm in diameter. An intricate protein structure called a pore complex lines each pore and plays an important role in the cell by regulating the entry and exit of proteins and RNAs, as well as large complexes of macromolecules. the nuclear side of the envelope is lined by the nuclear lamina, a netlike array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope.

Chromosomes/chromatin

A doubled rod of condensed chromatin; contains DNA that carries genetic information Within the nucleus, the DNA is organized into discrete units called chromosomes, structures that carry the genetic information. The complex of DNA and proteins making up chromosomes is called chromatin. When a cell is not dividing, stained chromatin appears as a diffuse mass in micrographs, and the chromosomes cannot be distinguished from one another, even though discrete chromosomes are present. As a cell prepares to divide, however, the chromosomes coil (condense) further, becoming thick enough to be distinguished under a microscope as separate structures Each eukaryotic species has a characteristic number of chromosomes. For example, a typical human cell has 46 chromosomes in its nucleus

major differences between prokaryotic and eukaryotic cells

A major difference between prokaryotic and eukaryotic cells is the location of their DNA:In a eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane. In a prokaryotic cell, the DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid The interior of either type of cell is called the cytoplasm; in eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane. suspended in cytosol, are a variety of organelles of specialized form and function. These membrane-bounded structures are absent in prokaryotic cells, another distinction between prokaryotic and eukaryotic cells. prok. cells appear to be organized into different regions.

Cell Fractionation

A useful technique for studying cell structure and function is cell fractionation: takes cells apart and separates major organelles and other subcellular structures from one another The piece of equipment that is used for this task is the centrifuge, which spins test tubes holding mixtures of disrupted cells at a series of increasing speeds. Cell fractionation enables researchers to prepare specific cell components in bulk and identify their functions, a task not usually possible with intact cells.

Smooth endoplasmic reticulum

Aids in making and transporting lipids and breaking down toxic substances Smooth ER is so named because its outer surface lacks ribosomes. Factory processing operations, many metabolic processes, synthesis & hydrolysis enzymes of smooth ER... synthesize lipids, oils, phospholipids, steroids & sex hormones, hydrolysis (breakdown) of glycogen (in liver) into glucose, detoxify drugs & poisons (in liver) ex. alcohol & barbiturates

The Extracellular Matrix (ECM) of Animal Cells

Although animal cells lack walls akin to those of plant cells, they do have an elaborate extracellular matrix (ECM). The main ingredients of the ECM are glycoproteins and other carbohydrate-containing molecules secreted by the cells. (Recall that glycoproteins are proteins with covalently bonded carbohydrates, usually short chains of sugars.) The most abundant glycoprotein in the ECM of most animal cells is collagen, which forms strong fibers outside the cells. In fact, collagen accounts for about 40% of the total protein in the human body. The collagen fibers are embedded in a network woven out of proteoglycans collagen fibers in network of glycoproteins.... support adhesion movement regulation Cell Junctions

vacuole

Cell organelle that stores materials such as water, salts, proteins, and carbohydrates. Large in plants Function as little "transfer ships" Food vacuoles • phagocytosis, fuse with lysosomes Contractile vacuoles • in freshwater protists, pump excess H2O out of cell Central vacuoles • in many mature plant cells Vacuoles perform a variety of functions in different kinds of cells. Many unicellular eukaryotes living in fresh water have contractile vacuoles that pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell In plants and fungi, certain vacuoles carry out enzymatic hydrolysis, a function shared by lysosomes in animal cells. In plants, small vacuoles can hold reserves of important organic compounds, such as the proteins stockpiled in the storage cells in seeds. Vacuoles may also help protect the plant against herbivores by storing compounds that are poisonous or unpalatable to animals. Some plant vacuoles contain pigments, such as the red and blue pigments of petals that help attract pollinating insects to flowers. Mature plant cells generally contain a large central vacuole. The solution inside the central vacuole, called cell sap, is the plant cell's main repository of inorganic ions, including potassium and chloride. The central vacuole plays a major role in the growth of plant cells as the vacuole absorbs water, enabling the cell to become larger

cell junctions

Cells in an animal or plant are organized into tissues, organs, and organ systems. Neighboring cells often adhere, interact, and communicate via sites of direct physical contact. All three types of cell junctions are especially common in epithelial tissue, which lines the external and internal surfaces of the body. tight junctions: membranes of adjacent cells fused forming barrier between cells forces material through cell membrane At tight junctions, the plasma membranes of neighboring cells are very tightly pressed against each other, bound together by specific proteins Forming continuous seals around the cells, tight junctions establish a barrier that prevents leakage of extracellular fluid across a layer of epithelial cells. For example, tight junctions between skin cells make us watertight gap junctions/communicating junctions: allow cytoplasmic movement between adjacent cells Gap junctions (also called communicating junctions) provide cytoplasmic channels from one cell to an adjacent cell and in this way are similar in their function to the plasmodesmata in plants Gap junctions consist of membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass. Gap junctions are necessary for communication between cells in many types of tissues, such as heart muscle, and in animal embryos. desmosomes/ anchoring junctions: fasten cells together in strong sheets Desmosomes (also called anchoring junctions) function like rivets, fastening cells together into strong sheets. Intermediate filaments made of sturdy keratin proteins.. anchor desmosomes in the cytoplasm. Desmosomes attach muscle cells to each other in a muscle. Some "muscle tears" involve the rupture of desmosomes

Peroxisomes

Chloroplasts and mitochondria cooperate with peroxisomes in certain metabolic functions The peroxisome is a specialized metabolic compartment bounded by a single membrane. Peroxisomes contain enzymes that remove hydrogen atoms from various substrates and transfer them to oxygen Specialized peroxisomes called glyoxysomes are found in the fat-storing tissues of plant seeds. These organelles contain enzymes that initiate the conversion of fatty acids to sugar, which the emerging seedling uses as a source of energy and carbon until it can produce its own sugar by photosynthesis.

endosymbiont theory

Dividing mitochondria Mitochondria and chloroplasts display similarities with bacteria that led to the This theory states that an early ancestor of eukaryotic cells engulfed an oxygen-using nonphotosynthetic prokaryotic cell. Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont (a cell living within another cell). Indeed, over the course of evolution, the host cell and its endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion. At least one of these cells may have then taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells This theory is consistent with many structural features of mitochondria and chloroplasts. First, rather than being bounded by a single membrane like organelles of the endomembrane system, mitochondria and typical chloroplasts have two membranes surrounding them

EM vs LM

Electron microscopes have revealed many subcellular structures that were impossible to resolve with the light microscope. But the light microscope offers advantages, especially in studying living cells. A disadvantage of electron microscopy is that the methods used to prepare the specimen kill the cells.

chloroplasts

Function: photosynthesis, generate ATP & synthesize sugars, transform solar energy into chemical energy, produce sugars from CO2 & H2O Chloroplasts are plant organelles: store chlorophyll (green pigment) along with enzymes and other molecules that function in the photosynthetic production of sugar The chloroplast is a specialized member of a family of closely related plant organelles called plastids. One type of plastid, the amyloplast, is a colorless organelle that stores starch (amylose), particularly in roots and tubers. Another is the chromoplast, which has pigments that give fruits and flowers their orange and yellow hues. The membranes of the chloroplast divide the chloroplast space into three compartments: the intermembrane space, the stroma, and the thylakoid space. Inside the chloroplast is membranous system in the form of flattened, interconnected sacs called thylakoids (membranous sacs where ATP is made). In some regions, thylakoids are stacked like poker chips; each stack is called a granum (plural, grana). The fluid outside the thylakoids is the fluid filled stroma (Chloroplasts DNA, ribosomes & enzymes). Semi-autonomous: moving, changing shape & dividing, can reproduce by pinching in two (just like bacteria)

golgi bodies (apparatus)

Golgi apparatus consists of flattened membranous sacs—cisternae—looking like a stack of pita bread finishes, sorts, & ships cell products "shipping & receiving department" center of manufacturing, warehousing, sorting & shipping 2 sides = 2 functions cis = receives material by fusing with vesicles = "receiving" trans = "transport" • During path from cis to trans, products from ER are modified into final form

Centrosomes/Centrioles

In animal cells, microtubules grow out from a centrosome, a region that is often located near the nucleus. Within the centrosome is a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring an organelle that is found close to the nucleus within the cytoplasm of cells. Centrosomes are key to the division of cells and produce the spindle fibers that are required during metaphase of mitosis.

Magnification

Magnification is the ratio of an object's image size to its real size

microscopes

Microscopes were invented in 1590. Cell walls were first seen by Robert Hooke in 1665 as he looked through a microscope at dead cells from the bark of an oak tree. Lenses of Antoni van Leeuwenhoek first to visualize living cells.

Microtubules

Microtubules are the thickest of the three types of cytoskeleton fibers hollow rods about 25nm in diameter constructed of protein, tubulin Each tubulin protein is a dimer, a molecule made up of two subunits. A tubulin dimer consists of two slightly different polypeptides, α-tubulin and β-tubulin grow or shrink as more tubulin molecules are added or removed move chromosomes during cell division

mitochondria and chloroplasts

Mitochondria (singular, mitochondrion) are the sites of cellular respiration, the metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats, and other fuels. Chloroplasts, found in plants and algae, are the sites of photosynthesis. This process in chloroplasts converts solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water. In eukaryotic cells, mitochondria and chloroplasts are the organelles that convert energy to forms that cells can use for work.

Rough endoplasmic reticulum

Modifies and transports proteins rough ER is studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope

Endoplasmic Reticulum (ER)

The endoplasmic reticulum (ER) is such an extensive network of membranes that it accounts for more than half the total membrane in many eukaryotic cells. manufactures membranes & performs many bio-synthesis functions There are two distinct, though connected, regions of the ER that differ in structure and function: smooth ER and rough ER.

Light microscopes (LM)

The microscopes first used by Renaissance scientists, as well as the microscopes you are likely to use in the laboratory, are all light microscopes. -visible light is passed through the specimen and then through glass lenses. The lenses refract (bend) the light in such a way that the image of the specimen is magnified as it is projected into the eye Light microscopes can magnify effectively to about 1,000 times the actual size of the specimen the light microscope cannot resolve detail finer than about 0.2 micrometer (μm), or 200 nanometers (nm), regardless of the magnification.

plant cell wall

The wall protects the plant cell, maintains its shape, and prevents excessive uptake of water. On the level of the whole plant, the strong walls of specialized cells hold the plant up against the force of gravity. Prokaryotes, fungi, and some unicellular eukaryotes also have cell walls. Cellulose: an insoluble substance that is the main constituent of plant cell walls and of vegetable fibers such as cotton. It is a polysaccharide consisting of chains of glucose monomers. primary cell wall: A young plant cell first secretes a relatively thin and flexible wall called the primary cell wall. Between primary walls of adjacent cells is the middle lamella which is made of sticky polysaccharides. secondary cell wall: Other cells add a secondary cell wall between the plasma membrane and the primary wall. The secondary wall, often deposited in several laminated layers, has a strong and durable matrix that affords the cell protection and support. plasmodesmata = channels allowing cytosol to pass between cells

All cells share certain basic features (4)

They are all bounded by a selective barrier, called the plasma membrane. Inside all cells is a semifluid, jellylike substance called cytosol, in which subcellular components are suspended. All cells contain chromosomes, which carry genes in the form of DNA. And all cells have ribosomes, tiny complexes that make proteins according to instructions from the genes.

microscope parameters

Three important parameters in microscopy are magnification, resolution, and contrast.

mitochondria

bean shaped organelle that helps produce the energy a cell needs --> from glucose to ATP in the presence of oxygen: break down larger molecules into smaller to generate energy = catabolism generate energy in presence of O2 = aerobic respiration has, 2 membranes. Smooth outer membrane and highly folded inner membrane called the cristae fluid-filled space between 2 membranes: The inner membrane divides the mitochondrion into two internal compartments. The first is the intermembrane space, the narrow region between the inner and outer membranes. The second compartment, the mitochondrial matrix, is enclosed by the inner membrane. The matrix contains many different enzymes as well as the mitochondrial DNA and ribosomes. Almost all eukaryotic cells have mitochondria, there may be 1 very large mitochondrion or 100s to 1000s of individual mitochondria number of mitochondria is correlated with aerobic metabolic activity

nucleus

oval organelle that is the cell's command center, contains genetic material which direct all cell activities The nucleus contains most of the genes in the eukaryotic cell. (Some genes are located in mitochondria and chloroplasts.) averaging about 5 μm in diameter. The nuclear envelope encloses the nucleus , separating its contents from the cytoplasm. The nucleus is on such vital importance to the cell because it contains the DNA that the cell needs to synthesize proteins and regulate mostly every other aspect of its function It also contains the Nucleolus, an organelle responsible for the production ribosomes for the cell.

Cilia and Flagella

specialized arrangement of microtubules is responsible for the beating of flagella (singular, flagellum) and cilia (singular, cilium) microtubule-containing extensions that project from some cells. move unicellular & small multicellular organisms by propelling water past them cilia sweep mucus & debris from lungs...oar like movement flagellum of sperm cells Though different in length, number per cell, and beating pattern, motile cilia and flagella share a common structure. Each motile cilium or flagellum has a group of microtubules sheathed in an extension of the plasma membrane. Nine doublets of microtubules are arranged in a ring, with two single microtubules in its center ...This arrangement, referred to as the "9 + 2" pattern, is found in nearly all eukaryotic flagella and motile cilia. so....9 pairs of microtubules around 2 single microtubules in center bending of cilia & flagella is driven by motor protein called dynein that are attached along each outer microtubule doublet. A typical dynein protein has two "feet" that "walk" along the microtubule of the adjacent doublet, using ATP for energy

Intermediate filaments

specialized for bearing tension built from keratin proteins, same protein as hair intermediate in size 8-12nm Function: hold "things" in place inside cell more permanent fixtures of cytoskeleton reinforce cell shape & fix organelle location nucleus is held in place by a network of intermediate filaments

transmission electron microscope (TEM)

used to study the internal structure of cells

endomembrane

the endomembrane system regulates protein traffic and preforms metabolic functions in a cell Many of the different membranes of the eukaryotic cell are part of the endomembrane system, which includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane. This system carries out a variety of tasks in the cell, including synthesis of proteins, transport of proteins into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons. The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles

Cell Specialization

the process in which cells develop in different ways to perform different tasks

cytoplasm

thick, jelly-like material which contains and supports cell organelles

Microfilaments (Actin Filaments)

thinnest class of fibers solid rods of protein, actin twisted double chain of actin subunits about 7nm in diameter Function: 3-D network inside cell membrane, in muscle cells, actin filaments interact with myosin filaments to create muscle contraction actin filaments constantly form & dissolve making the cytoplasm liquid or stiff during movement....movement of Amoeba cytoplasmic streaming in plant cells In plant cells, both actin-myosin interactions contribute to cytoplasmic streaming, a circular flow of cytoplasm within cells. This movement is especially common in large plant cells.

plasma membrane

very thin layer of protein and fat that forms a border around the cell The plasma membrane and organelle membranes also participate directly in the cell's metabolism, because many enzymes are built right into the membranes. The basic fabric of most biological membranes is a double layer of phospholipids and other lipids However, each type of membrane has a unique composition of lipids and proteins suited to that membrane's specific functions.