The Cell and Its Components

Question 1

Describe the structure and function of the nucleus

Answer 1

• Stores and replicates the genetic information of the cell
• Is surrounded by a nuclear envelope which consists of 2 phospholipid bilayers to separate the nucleus from the rest of the cell

Question 2

What is the importance of the nuclear envelope?

Answer 2

• Studded with thousands of nuclear pore complexes, which form openings in the envelope
• Allows ions, water, and other small particles though the openings

Question 3

Describe the structure and function of the endoplasmic reticulum

Answer 3

• The surface is devoted to synthesizing proteins which are studded by ribosomes
• Molecular aggregates of protein and RNA

Question 4

What is the function of the smooth ER?

Answer 4

• Synthesizes and metabolizes lipids and other lipid-containing molecules like phospholipids
• Can perform other functions, depending on the type of cell

Question 5

Describe the structure and function of the vesicles

Answer 5

• Pieces off of the smooth ER which pinch off and form
  -Used for transport and storage
• A membrane-enclosed sac

Question 6

Describe the structure and function of the Golgi apparatus

Answer 6

• A curved stack of membrane sacs
• Packages, processes, sorts, and distributes proteins, lipids, and other substances within the cell

Question 7

Describe the structure and function of lysosomes

Answer 7

• A membrane-enclosed sac
• Contains enzymes that catalyze the hydrolysis of reactions by breaking down macromolecules

Question 8

Describe the structure and function of peroxisomes

Answer 8

• A membrane-enclosed sac
• Contains an oxidative enzyme that breaks down excess fatty acids and hydrogen peroxide
• Can help produce bile and cholesterol

Question 9

Describe the structure and function of the vacuole

Answer 9

• A large membrane-bound sac
• Only found in plants
• Stores amino acids, sugars, macromolecules, water, and ions
• Determines the turgor pressure of the plant depending on the plants water intake

Question 10

Describe the structure and function of the mitochondria

Answer 10

Breaks down high-energy molecules to break them down to convert stored energy into usable energy

Question 11

Describe the structure and function of chloroplast

Answer 11

• Contains photosynthetic pigment
• Absorbs light energy which converts carbon dioxide and water through redox reactions
• Stores glucose

Question 12

Describe the structure and function of the cell wall

Answer 12

• Used for protection and support
• Only found in plant cells
• Around the outside of the cell
• Composed of polysaccharides, glycoproteins, or both

Question 13

Describe the structure and function of the cytoskeleton

Answer 13

• A network of protein fibres which extends throughout the cytosol
• Provides the cell with structure, shape, support and mobility

Question 14

What are the 3 structures in the endomembrane system?

Answer 14

1. Vesicles
2. Golgi Apparatus
3. Lysosomes

Question 15

What is the structure and function of cilia and flagella? How is their structure slightly different?

Answer 15

• A long, thin appendage which allows cells to move themselves or move substances over their surface
• Cilia: Small hair-like projections
• Flagella- Has a long, whip-like tail

Question 16

What does the fluid mosaic model depict?

Answer 16

• A model of the basic framework of a semi-fluid phospholipid bilayer
• Represents the proteins and substances that are able to pass through

Question 17

What are the important features of the fluid mosaic model?

Answer 17

• The mosaic section depicts proteins and other macromolecules
• The fluid section depicts the membranes in the molecule that can move freely
• Contains the phospholipid bilayer

Question 18

Explain the structure and components of the phospholipid bilayer

Answer 18

• Composed of one glycerol and 2 fatty acids, and a highly polar phosphate group
  Head: Polar, hydrophilic
  Tail: Non-polar, hydrophobic
• Held together by intermolecular interactions
• Polar heads face out, toward the aqueous environment

Question 19

What are the 4 main factors that affect the fluidity of the phospholipid bilayer?

Answer 19

1. Temperature
2. % of Unsaturated Fatty Acids in Phospholipids
3. Fatty Acid Tail Length
4. Cholesterol in Membrane

Question 20

What is the difference between peripheral and integral proteins?

Answer 20

Integral: Embedded in the membrane
Peripheral: Loosely and temporarily attached to outer regions of the membrane, or to integral proteins

Question 21

How do peripheral and integral proteins work?

Answer 21

-Help stabilize membranes
- Holding them in place by linking them to the cytoskeleton of the cell

Question 22

What is the difference between passive and active transport?

Answer 22

Passive: The movement of ions/molecules across a cell membrane from a region of higher to lower concentration without energy
Active: The transport of a solute across its membrane with the use of energy (ATP)

Question 23

What is the difference between diffusion and osmosis?

Answer 23

Diffusion: The net movement of ions/ molecules from an area of high to low concentration
Osmosis: The movement of water from an area of high to low concentration across a semi-permeable membrane

Question 24

Explain the passive transport by diffusion

Answer 24

• The net movement of ions/molecules from an area of high to low concentration
• Its goal is to meet an equilibrium on both sides of the membrane

Question 25

Explain the passive transport by osmosis

Answer 25

- The movement of water from an area of high to low concentration across a semi-permeable membrane - Water molecules move in and out of the cell until both sides reach an equilibrium

Question 26

Explain the structure and condition of a cell in an isotonic solution

Answer 26

- Animal cell is immersed in mild salt solution - Cell is flaccid - No net diffusion of water

Question 27

Explain the structure and condition of a cell in a hypertonic solution

Answer 27

- Cell is in salt water - Cell is plasmolyzed/shriveled - If plant cells are plasmolyzed, they wilt

Question 28

Explain the structure and condition of a cell in a hypotonic solution

Answer 28

- A cell in freshwater - Cell is turgid - Can potentially burst (lysis)

Question 29

Explain the passive transport by facilitated diffusion

Answer 29

The transport of ions or molecules across a membrane using a membrane protein along the concentration gradient for that ion or molecule

Question 30

What is a channel protein and what is its function?

Answer 30

- Diffuses through protein channels - Allows specific ions or molecules to cross the membrane along their concentration gradients

Question 31

Explain the process of primary active transport

Answer 31

- Uses ATP to transport molecules or ions from one side of the membrane to the other - Use carrier proteins instead of channel proteins - Ion pumps are carrier proteins that use ATP to “pump” ions across the membrane against a concentration gradient

Question 32

What is a carrier protein and what is its function?

Answer 32

- Binds to specific molecules and transports them across the membrane, which is released on the other side - Changes shape while transporting molecules

Question 33

Explain the process of secondary active transport

Answer 33

- Uses an existing gradient to actively transport another substance - As an ion pump functions, a concentration gradient forms across the membrane - A difference in charge or electric potential builds up across the membrane - The electrochemical gradient created by primary active transport via an ion pump is used by a different protein to transport other molecules across a cell membrane

Question 34

Explain the structure and hydrolysis of ATP

Answer 34

- A source of energy used in active transport - Composed of an adenosine nucleotide, with a triple phosphate group - ATP hydrolyzes to form ADP, which releases energy

Question 35

What is endocytosis?

Answer 35

- Cell membrane engulfs extracellular material to bring it inside the cell - Pinches off to form vesicles inside the cell

Question 36

What is exocytosis?

Answer 36

- Vesicles fuse with the cell membrane and empty its contents into the extracellular environment - Vesicle becomes part of the cell membrane - In animal cells, exocytosis is used to release substances such as hormones, neurotransmitters, and digestive enzymes

Question 37

What is phagocytosis

Answer 37

- Endocytosis involving solid particles - Known as cell eating - Forms large vesicles or vacuoles

Question 38

What is pinocytosis?

Answer 38

- Endocytosis involving liquid particles - Known as cell drinking - Forms small pinocytic vesicles

Question 39

Explain the process of the sodium-potassium pump

Answer 39

1. 3 cytoplasmic sodium binds to the Na/K pump 2. The sodium bind stimulates phosphorylation by ATP 3. Phosphorylation causes the protein to lose its original conformation, expelling the sodium outside 4. 2 extracellular potassiums bind to the protein, causing a release of a phosphate group 5. The loss of a phosphate group results in the protein regaining its original conformation 6. Potassium is expelled and sodium sites are receptive, repeating the cycle again

Question 40

What kind of transport is endocytosis and exocytosis?

Answer 40

Membrane-assisted transport

Question 41

Explain the permeability of the phospholipid bilayer

Answer 41

- Impermeable to macromolecules - Slightly permeable to ions - Quite permeable to small, lipid-containing molecules - Permeable to CO2 and O2 - Larger molecules pass through the membrane using carrier proteins

Question 42

Explain how temperature affects the fluidity of the phospholipid bilayer

Answer 42

- Increased temperature, increased fluidity - Decreased temperature, decreased fluidity, forming a gel-like state

Question 43

Explain how the % of unsaturated fatty acids in phospholipids affects the fluidity of the phospholipid bilayer

Answer 43

- Double bonds create kinks in the fatty acid tail - More double bonds cause fatty acids to be more fluid

Question 44

Explain how fatty acid tail length affects the fluidity of the phospholipid bilayer

Answer 44

- Longer fatty acid tails have more intermolecular attractions - They hold tightly together, decreasing fluidity

Question 45

Explain how the cholesterol of the membrane affects the fluidity of the phospholipid bilayer

Answer 45

- Acts as a “mortar” that fills in small gaps in the phospholipid structure, improves membrane impermeability to small water molecules like glucose - Acts as a membrane “antifreeze gel”, decreases fluidity at high temperatures and increases fluidity at low temperatures

Question 46

What is the difference between what channel and carrier proteins transport?

Answer 46

Channel: Transports ions or small polar molecules across the membrane Carrier: Tansports large molecules-glucose, amino acids

Question 47

What are aquaporins?

Answer 47

- Water moves rapidly in and out of the cell - Water movement through aquaporins is a passive process that follows the direction of osmotic pressure across the membrane

Question 48

The sodium-potassium pump is an example of what kind of transport?

Answer 48

Primary active transport