Cells

Question 1

What are the three main components of phospholipids, and what are their characteristics?

Answer 1

Phosphate head. (Hydrophilic)
Glycerol backbone (holds the tails to the head)
Fatty acid tails (2) (hydrophobic)

Question 2

What is the term which describes a molecule which has both a hydrophilic and hydrophobic parts?

Answer 2

Amphipathic

Question 3

Describe how the phosphate molecule are oriented in the cell wall.

Answer 3

In a double line, phosphate head groups face both out into extracellular and into intracellular space.

Question 4

The cell membrane is semi-permeable: What kinds of molecules pass best through it?

Answer 4

Small, non-polar molecules pass through via passive diffusion.

Question 5

Describe the speed of passage through the cell membrane of the following via passive diffusion: Small, non-polar molecules, small, polar molecules, large, non polar molecules, large, polar molecules, and charged molecules.

Answer 5

Small, non-polar molecules (such as gases) pass quickly.

Small, polar molecules (such as H2O and Ethanol) pass through slowly.

Large, non polar molecules (benzene) pass slowly.

Large, polar molecules (glucose) do not pass.

Charged ions (Cl, Na, or amino acids) do not pass.

Question 6

On a molecular level, what comprises a phospholipid?

Answer 6

Tails: Fatty acid: A Carboxylic Acid and a long carbon chain (R group)

Glycerol backbone

Polar Headgroup: phosphate

Question 7

Describe the chemical diagram of the fatty acid tail of a phospholipid:

Answer 7

Carbon with a double bond to an O and a single bond to an OH, and a long carbon chain labeled as the R group.

Question 8

Describe the chemical diagram for the phospholipid chemical backbone.

Answer 8

3 Carbons attached to each other, with a single OH bonded to each

Question 9

Describe the chemical diagram of a phospholipid’s polar head group.

Answer 9

A phosphate, with 4 single bonds to 4 negatively charged oxygen ions.

Question 10

In the context of the carbon tail of a phospholipid, what is the difference between a cis and trans bond?

Answer 10

In a cis bond, there is a double bonded carbon, each of which is connected to a carbon, and those two carbons are on the same side. In a trans bond, there is a double bonded carbon, each of which is connected to a carbon, and those two carbons are on opposite sides.

Question 11

In a phospholipid, the polar head can bond with other molecules; how does this happen?

Answer 11

When becoming a phospholipid molecule, the one of the oxygens on the phosphate head bonds with a hydrogen. This hydroxyl group is the bonding point with other molecules, creating a diverse array of molecules in the cell wall.

Question 12

What 3 substances are found in the cell membrane?

Answer 12

• Phospholipids (arranged in lipid bilateral)
• Cholesterol (maintain fluidity if cell wall aka homeostasis as temperatures change)
• Proteins (integral aka transmembrane protein crosses both layers, and peripheral proteins sit on one layer of the cell wall)

Question 13

What is the function of proteins in the cell wall?

Answer 13

They act as receptors, and facilitate transport of molecules that cannot pass through the lipid bilayer.

Question 14

What role to carbohydrates play in the cell wall?

Answer 14

They bind to either proteins or phospholipids can be either glycolipids or glycolipids. They play a role in communications (cells recognizing other cells).

Question 15

Describe the fluid mosaic model.

Answer 15

The cell wall is made up of phospholipids, cholesterol, proteins, and carbohydrates. They are not fixed in one place, and there is some movement of the different components around the cell wall.

Question 16

What is the name of a protein which is found between the lipid bilayer?

Answer 16

Lipid bound protein.

Question 17

What three different categorization songs based on functions of protein in the cell wall?

Answer 17

Channel proteins- facilitate movement of ions through cell wall down the concentration gradient. No energy needed.
Carrier proteins- Allow transport of molecules against the concentration gradient. Sometimes use energy (ATP)
Glycoproteins- communication.

Question 18

What three factors affect membrane fluidity and how?

Answer 18

Temperature- cold temperature leads to less fluidity (at extreme, membrane reaches a crystallized state).
Cholesterol- cholesterol increases fluidity when cold, and increases fluidity when warm (as loosely bound phospholipids are drawn together).
Saturated vs unsaturated fatty acids- Saturated fatty acid has a more consistent shape, leading to less membrane fluidity. Unsaturated fatty acids don’t stack as well, increasing fluidity.

Question 19

In membrane dynamics, what are the ways that phospholipids can move?

Answer 19

Uncatalyzed:
- translayer diffusion (moving from one layer to another. Slow process. Aka “flip-flop”.)
- Lateral diffusion (changing position within its layer. Fast).
Catalyzed:
- Moving from extra- to intra-cellular level, or reverse (flippase and floppase, respectively). Uses ATP as fuel. Happens quickly.
- Exchange positions of a phospholipid from intra- and extra-cellular layers. Does not require ATP. Occurs quickly, due to a protein acting as catalyst. Enzyme is scramblase.

Question 20

Differentiate between the actions of flippase and floppase.

Answer 20

Flippase: Phospholipid on extracellular layer “flips” to intracellular layer, utilizing a catalyst and ATP.

Floppase: Phospholipid on intracellular layer moves to extracellular layer, utilizing a catalyst and ATP.

(Flip- end state of the phospholipid is inside. Flop- end state of the phospholipid is outside)

Question 21

Describe the three main types of cell junctions, and where each type might be found:

Answer 21

Tight junctions- cells are not physically connected, but are pushed together rightly enough to not permit ions or water to flow between. Found in areas such as bladder, kidneys, and intestines.
Desmosomes- There is space between the cells, but they are attached together by connections which are attached to each cell’s cytoskeleton. Allows some flexibility and flow of materials. Found in skin, intestines.
Gap Junctions- there is a physical joining between cells, allowing rapid exchange of ions and water. Found in cells which need to conduct action potentials, such as cardiac cells and nerves.

Question 22

What are the characteristics of a membrane receptor?

Answer 22

• Integral protein

- Communicates with outside environment.

Question 23

Describe the process of Signal Transduction.

Answer 23

• A ligand (Ion/molecule used for communication) binds with a membrane receptor, forming a ligand-receptor complex.
• After binding, there is an intracellular response. (Cascade of protein signalling).

Question 24

Describe the two models of the signal transduction process.

Answer 24

Lock-and-key: A given ligand and membrane receptor have a specific fit, and one only first with the other.

Induced fit: There is some flexibility, and the ligand and membrane receptors can change conformations slightly to fit each other.

Question 25

What are the three types of membrane receptors?

Answer 25

• Ligand-gated ion channels
• G-protein coupled receptors
• Enzyme Receptors

Question 26

What is the other term for Ligand-gated ion channel?

Answer 26

Ion channel linked receptors.

Question 27

Where are ligand-gated ion channels most commonly found?

Answer 27

In electrically excitable cells (such as neutrons), as these cells react quickly to binding with ligands.

Question 28

Describe the mechanism by which ligand-gated ion channels work.

Answer 28

A transmembrane protein has an allosteric (away from the ion channel) receptor which responds to a ligand. When that receptor is stimulated, a channel opens due to a change in the protein conformation of the entire protein, allowing ions to move through the open channel.

Question 29

What are the most-common ions to move through a ligand-gated ion channel?

Answer 29

K, Na, Cl, and Ca. These cause an electrical signal in the cell.

Question 30

What is the other name for G-protein coupled receptors?

Answer 30

7 Transmembrane receptors

So named because they cross the membrane 7 times (7 transmembrane alpha helixes)

Question 31

Describe G proteins.

Answer 31

Specialized proteins which can combine guanosine triphosphate and guanosine diphosphate (GTP and GDP).

Question 32

What type of G proteins bind with GPCRs.

Answer 32

They must be heterotrimeric. Comprise 3 subunits (alpha, beta, and gamma subunits. Alpha and gamma subunits are attached to cell membrane by lipid anchors).

Question 33

Describe the process of GPCR activation (6 steps)

Answer 33

1. Ligand binds to GPCR
2. GPCR undergoes “conformational change”
3. Alpha subunit exchanges GDP for GTP
4. Alpha subunit dissociates and regulates target proteins. (Beta-Gamma diner can also regulate functions of other proteins).
5. Target protein relays a signal via second messenger.
6. GTP is hydrolyzed to GDP, returning GPCR to its’ original state.

Question 34

What are enzymes?

Answer 34

A substance in bodies that acts as a catalyst, which can speed up certain biochemical processes.

Question 35

What is the most widely recognized and common type of enzyme-linked receptor, and what do they do?

Answer 35

Receptor Tyrosine Kinases.

Regulate cell-growth, differentiation, and survival. Combine with and respond to ligands including growth factors.

Question 36

Describe the structure of Receptor Tyrosine Kinases.

Answer 36

RTKs occur in pairs (or more).

In the intracellular portion of the transmembrane receptor, there are tyrosine kinases.

When activated by a signalling molecule, the two RTKs combine to form a cross-linked dimer.

This cross-linked dimer leads to cross-phosphorylation. Tyrosines cause intracellular ATP to become ADP + P. Tyrosines then pick up the free-floating phosphates.

Cross-phorylated enzymatic sections serve as docking platforms for different intracellular proteins involved in signal transduction (different proteins can attach to phosphorylated tyrosines)

Often, bound proteins lead to signal transduction into cytosol, often ultimately leading to gene transcription and subsequent protein production.

Question 37

What effect are RTKs best known for?

Answer 37

Role in growth factors, such as regulating surface proteins.

RTKs also bind hormones, including insulin.

Question 38

Describe the process of the Na/K Pump.

Answer 38

Allows Na and K to travel in/out of cell against the concentration gradient, utilizing the energy from breaking an ATP into ADP + P. Can also be called a sodium/potassium ATPase.

Question 39

Differentiate between primary and secondary active transport.

Answer 39

Primary active transport: Directly uses ATP to fuel transport.

Secondary active transport. (Uses a gradient that has already been set up using energy).

Question 40

Detail the difference between symport and anti port.

Answer 40

In symport, an ion(such as sodium) travels along its concentration gradient into a cell, and another substance enters in the same direction with it.

In antiport (for example, for a substance to enter a capillary), sodium travels into cell (with ion gradient), and another molecule travels in the opposite direction.

Question 41

Differentiate between endocytosis and exocytosis.

Answer 41

Endocytosis is a method for large substances to enter cells. A vesicle, for example carrying amino acids or a neurotransmitter, fuses cell membranes with target cells, allowing substance to enter cell. Uses energy.

Exocytosis. Same process, but it allows a substance to exit cell. Uses energy too.

Question 42

Summarize facilitated diffusion:

Answer 42

An extracellular ion binds with a transport protein in the cell wall.

It binds with that cell’s receptors. This binding stimulates the protein to change its conformation, and it flips, moving the opening in the cell from the extracellular space to the intracellular space.

The opening now being in the intracellular space allows the ion to move into the cell.

As the receptor is once more empty, it changes conformation again to orient the opening into the extracellular space.

Question 43

What is the difference between the solvent and the solute?

Answer 43

Solvent is the thing there is more of, solute is the thing there is less of, and solution is the combination.

Question 44

What is diffusion?

Answer 44

Movement of particles from high concentration to low concentration area within a space.

Question 45

Define osmosis.

Answer 45

Diffusion of water through a semi-permeable membrane to equalize concentration gradients (where the solute cannot travel through the membrane).

Question 46

What is the name of the capsule that captures filtrate from the glomerulus?

Answer 46

Bowman’s Capsule

Question 47

Describe the structure of the connection between the glomerulus and the Bowman’s capsule.

Answer 47

The blood vessel walls are endothelial cells (fenestrated, to allow substances through).

Basemen membrane is attached to endothelial cells, and prevents large proteins from exiting the blood vessels.

Tubular cells are at the edge of Bowman’s capsule. Some of the cells have “leg-like” projections which secure them to endothelial cells. These cells are called podocytes.

Question 48

Is the intra or extra-cellular space more electrically positive at rest, and by how much?

Answer 48

The extracellular space maintains a higher level of electrical positivity, with an approximate voltage difference of -70mV.

Question 49

What are the steps in the functioning of the sodium-potassium pump?

Answer 49

1. 3 Na+ from inside bond to pump (protein).
2. ATP turns into ADP and P, releasing energy to change pump shape.
3. Sodium is released outside the cell.
4. 2 K+ ions bond to changed form. This bonding re-changes the shape into original form.
5. 2 K+ released inside the cell.

Question 50

How is the resting electrical potential difference between the intracellular and extracellular space maintained?

Answer 50

Channels (protein structures), allow the passage of some potassium and some sodium, even when the channel is closed. This helps to maintain a consistent electrical potential.