Chapter 6 - The Cell (Part 2)

Question 1

What is a lysosome?

Answer 1

A membranous sac of hydrolytic enzymes that eukaryotic cells can use to digest (hydrolyze) macromolecules. Typically found in animal cells. Lysosomes digest materials taken into the cell and recycle intracellular materials.

*In plant cells and yeast, the same roles are performed by organelles known as lyric vacuoles.

Question 2

What can lysosomal enzymes hydrolyze?

Answer 2

Proteins, fats, polysaccharides, and nucleic acids. Lysosomal enzymes work best in an acidic environment.

Question 3

What is phagocytosis?

Answer 3

A process of intracellular digestion where amoebas and many other unicellular eukaryotes eat by engulfing smaller organisms or food particles. A lysosome fuses with the food vacuole and digests the molecules.

Question 4

What is the process of autophagy?

Answer 4

Lysosomes use enzymes to recycle the cells own organelles and macromolecules. 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.

Question 5

What are vacuoles?

Answer 5

Diverse maintenance compartments; large vesicles derived from the endoplasmic reticulum and Golgi apparatus.

Question 6

What are three types of vacuoles?

Answer 6

1. Food vacuole - formed by phagocytosis
2. Contractile vacuole - pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell. Found in many freshwater protists.
3. Central vacuole - found in many mature plant cells; holds organic compounds and water. Plays a major role in the growth of plant cells, which enlarge as the vacuole absorbs water, enabling the cell to become larger with a minimal investment in new cytoplasm.

Question 7

What is the endomembrane system?

Answer 7

A complex and dynamic player in the cell’s compartmental organization. Includes the following organelles;

1. Nuclear envelope
2. Endoplasmic reticulum
3. Golgi apparatus
4. Lysosomes
5. Plasma membrane

Question 8

What are mitochondria?

Answer 8

Convert energy to forms that cells can use for work. 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.

Found in nearly all eukaryotic cells and have a smooth outer membrane and inner membrane folded into cristae (cristae present a large surface area for enzymes that synthesize ATP). The inner membrane creates two compartments;

1. Intermembrane space
2. Mitochondrial matrix

The two membranes inclosing the mitochondria are phospholipid bilayers with a unique collection of embedded proteins

Question 9

What are chloroplasts?

Answer 9

Found in plants and algae and are the site of photosynthesis. Chloroplasts convert 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. Contain the green pigment chlorophyll. The chloroplast is a member of a family of organelles called plastids.

Question 10

What are 4 similarities between mitochondria and chloroplasts?

Answer 10

1. Not part of the endomembrane system
2. Have a double membrane
3. Have proteins made by free ribosomes
4. Contain their own DNA; autonomous organelles that grow and reproduce within the cell

Question 11

What is the endosymbiont theory?

Answer 11

This theory states that an early ancestor of eukaryotic cells engulfed an oxygen-using non-photosynthetic 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).

Question 12

What is cristae?

Answer 12

The inner membrane that divides the mitochondrion into two internal compartments.

1. Intermembrane space
2. Mitochondrial matrix - enclosed by the inner membrane. The matrix contains many different enzymes as well as the mitochondrial DNA with ribosomes. Enzymes in the matrix catalyze cellular respiration.

Question 13

What is contained in the structure of a chloroplast?

Answer 13

Double membranes separated by an intermembrane space partition the chloroplast from the cytosol.

1. Thylakoids - flattened, interconnected membranous sacs , stacked to form a granum
2. Stroma - the fluid outside the thylakoids, and contains the chloroplast DNA and ribosomes as well as many enzymes
   * The membranes of the chloroplast divide the chloroplast into three compartments; the intermembrane space, the stroma, and the thylakoid space*
   * Chloroplasts have dynamic behavior and are mobile and their shape is changeable. They move around the cell along tracks of the cytoskeleton*

Question 14

What are plastids? What are the three different types of plastid organelles?

Answer 14

Plastids are found in cells of photosynthetic eukaryotes and include a closely related family of three types of organelles;

1. Chloroplasts
2. Chromoplasts - pigments that give fruits and flowers their orange and yellow hues
3. Amyloplasts - a colorless organelle that stores starch (amylose)

Question 15

What are peroxisomes?

Answer 15

Specialized metabolic compartments bounded by a single membrane. Contain enzymes that remove hydrogen atoms from various substrates and transfer them to oxygen, producing hydrogen peroxide (H2O2) as a by product.

Peroxisomes contain more than 50 different types of enzymes, which are involved in a variety of biochemical pathways in different types of cells.

Hold on to enzymes that require oxygen. Some peroxisomes use oxygen to break fatty acids down into smaller molecules that are transported to mitochondria and used as fuel for cellular respiration.

Peroxisomes in the liver detoxify alcohol and other harmful compounds by transferring hydrogen from the poisons to oxygen.

*To provide a compartment for oxidation reactions, peroxisomes are involved in lipid biosynthesis.

Question 16

What is the cytoskeleton?

Answer 16

A network of fibers extending throughout the cytoplasm. It organizes the cells structures and activities, anchoring many organelles.

Question 17

What are the 3 types of molecular structures of the cytoskeleton?

Answer 17

1. Microtubules - hollow tubes; the thickets of the three components;
2. Microfilaments - the thinnest of the three components (aka actin filaments)
3. Intermediate filaments - fibers with diameters in a middle range

Question 18

What are the functions of the cytoskeleton?

Answer 18

1. Gives mechanical support to the cell and maintain its shape
2. Cell motility - Interacts with motor proteins to produce motility; includes both changes in cell location and movements of cell parts. Cytoskeleton elements and motor proteins work together with plasma membrane molecules to allow whole cells to move along fibers outside the cell.
3. Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton
4. May help regulate biochemical activities

Question 19

More specifically, what are microtubules? What are their functions?

Answer 19

Hollow rods constructed from a globular protein called tubulin. Each tubulin (dimer) is made up of two subunits, consisting of two slightly different polypeptides a (alpha) tubulin and B (beta) tubulin. Because of the orientation of these dimers, the two ends of a microtubule are slightly different and one end can accumulate or release tubulin dimers at a much higher rate than the other, thus growing and shrinking significantly during cellular activities.

1. Shape the cell - microtubules are responsible for maintenance of cell shape; cell motility (tracks);
2. Separates chromosomes during division - chromosome movements in cell division;
3. Guides movement in organelles - organelle movements *(guide vesicles from the ER to the Golgi apparatus and from the Golgi to the plasma membrane)

Question 20

In animal cells, what do microtubules grow out from?

Answer 20

Centrosome - a region that is often located near the nucleus. The microtubule organizing center. These microtubules function as compression resisting girders of the cytoskeleton.

Question 21

What are centrioles?

Answer 21

Within the centrosome is a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring.

Question 22

What is cilia and flagella?

Answer 22

In eukaryotes, a specialized arrangement of microtubules is responsible for the beating of cilia and flagella; microtubules containing extensions that project from some cells. These sometimes act as locomotor appendages and help many unicellular eukaryotes propel through water (i.e. sperm of animals, algae, and some plants have flagella). They can move fluid over the surface of a tissue as well (i.e. ciliated lining of the windpipe sweeps mucus containing trapped debris out of the lungs).

Question 23

How do cilia and flagella differ?

Answer 23

In their beating patterns. A flagellum has an undulating motion like the tail of a fish (*swimming). Longer than cilia. Limited to just one or a few per cell.

Cilia work more like oars, with alternating power and recovery strokes (*racing boat). Cilia also act as a signal receiving antenna for the cell and this function is generally nonmotile. there is only one per cell. Crucial to brain function and to embryonic development.

Question 24

What do cilia and flagella share in common?

Answer 24

Share a common ultrastructure;

1. A core of microtubules sheathed by the plasma membrane - 9 doublets of microtubules are arranged in a ring, with two single microtubules in its center (9 + 2) pattern. This pattern is found in nearly all eukaryotic flagella and motile cilia.
2. A basal body that anchors the cilium or flagella - microtubule triplets in a 9 + 0 pattern.
3. A motor protein called dynein, which drive their bending movements. A typical dynein has two “feet” that walk along the microtubule of the adjacent doublet, using ATP for energy. The movements of the dynein feet cause the microtubules - and the organelles as a whole - to bend.

Question 25

More specifically, what are microfilaments? What are their functions?

Answer 25

Thin solid rods about 7nm in diameter. Built as a twisted double chain of actin (globular protein) subunits.

1. Their structural role is to bear tension, resisting pulling forces in the cell.

They form a 3D network just inside the plasma membrane to help support the cells shape. This network gives the outer cytoplasmic layer of the cell (cortex) the semisolid consistency of a gel, in contrast with the more fluid state of the interior cytoplasm. Bundles of microfilaments make up the core of microvilli in intestinal cells.

2. Function in cellular motility - thousands of actin filaments and thicker filaments made up of myosin interact to cause contraction of muscle cells; the crawling movement of cells - the cell crawls along a surface by extending cellular extensions called pseudopodia (“false foot”) and moving toward them. *In muscle cells, thousands of actin filaments are arranged parallel to one another.
3. Drives amoeboid movement
4. In plant cells, actin-myosin interactions and solgel transformations drive cytoplasmic streaming

Question 26

What is cytoplasmic streaming?

Answer 26

A circular flow of cytoplasm within cells. This movement, which is especially common in large plant cells, speeds the distribution of materials within a cell.

Question 27

What is the cortex?

Answer 27

The outer cytoplasmic layer of the cell.

Question 28

More specifically, what are intermediate filaments? What are their functions?

Answer 28

Intermediate filaments are larger than microfilaments but smaller than microtubules. They range in diameter from 8-12 nm. (Only found in the cells of some animals)

A diverse class of cytoskeletal elements that specialize in bearing tension.

More permanent fixtures of cells than microfilaments and microtubules.

Support cell shape and fix organelles in place.

Question 29

What is the purpose of extracellular components?

Answer 29

Extracellular components and connections between cells help coordinate cellular activities.

Most cells synthesize and secrete materials that are external to the plasma membrane.

These extracellular structures include;

1. Cell walls of plants
2. The extracellular matrix (ECM) of animal cells
3. Intercellular junctions

Question 30

What is the cell wall?

Answer 30

An extracellular structure of plant cells that distinguishes them from animal cells. The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water.

Prokaryotes, fungi, and some protists have cell walls.

Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein. *Same basic structural design found in steel reinforced concrete and fiberglass.

Question 31

What are the three layers of the plant cell wall?

Answer 31

1. Primary cell wall - thin and flexible
2. Middle lamella - a thin layer, rich in sticky polysaccharides called pectins, between primary walls of adjacent cells (glues adjacent cells together) (*pectin as a thickening agent)
3. Secondary cell wall - in some cells; added between the plasma membrane and the primary cell wall; has a strong and durable matrix that affords the cell protection and support

Question 32

What is plasmodesmata?

Answer 32

Channels between adjacent plant cells. Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell.

Question 33

What is the extracellular matrix?

Answer 33

Animal cells lack cell walls, but are covered by an elaborate extracellular matrix (ECM). The ECM is made up of glycoproteins such as; collagen (forms strong fibers outside the cells and are embedded in a web of proteoglycan complexes), proteoglycans, and fibronectin.

ECM proteins bind to cell surface receptor proteins called integrins that are built into the plasma membrane.

Question 34

What are the functions of the extracellular matrix?

Answer 34

1. Support
2. Adhesion
3. Movement
4. Regulation

Question 35

What are integrins? What are their functions?

Answer 35

Membrane proteins with two subunits; bind to the ECM on the outside and to associated proteins attached to microfilaments on the inside of the cell. This linkage can transmit signals between the cell’s external environment and its interior and can result in changes in cell behavior.

Question 36

What is the importance of cell junctions?

Answer 36

Neighboring cells in tissues, organs, and organ systems, often adhere, interact, and communicate via sites of direct physical contact

Intercellular junctions facilitate this contact

Question 37

What are the four types of intercellular junctions?

Answer 37

Plant cells
1. Plasmodesmata

Animal cells
2. 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 (i.e. tight junctions between skin cells make us watertight).

3. Desmosomes - 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. They resist mechanical stress because of their strong adhesive properties.
4. Gap 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.