B2.1 Cells

Question 1

What is the phospholipid bilayer?

Answer 1

Phospholipids are the basis of membrane structure.

Head is water loving
Tail is water hating

Question 2

What are fatty acids composed of?

Answer 2

Fatty acids are chains of hydrogen and carbon atoms termed as a hydrocarbon chain

These hydrocarbon chains can be either saturated or unsaturated

Question 3

Diffusion

Answer 3

Net movement of molecules from a region of high concentration to a region of low concentration. This directional movement along a concentration gradient is passive and will continue until molecules become evenly dispersed (equilibrium)

Question 4

How do hydrophilic water molecules cross the hydrophobic interior of the bilayer?

Answer 4

Carrier proteins

Question 5

Integral proteins

Answer 5

Penetrate the phospholipid bilayer to remain attached to the membrane

Question 6

Peripheral proteins

Answer 6

Only temporarily associated with one side of a membrane

Question 7

Membrane protein functions

Answer 7

Junctions - serve to connect and join two cells together.

Enzymes - fixing to membrane localises metabolic pathways

Transport - responsible for facilitated diffusion and active transport

Recognition - may function as markers for cellular identification

Anchorage - attachment points for cytoskeleton and extracellular matrix

Transduction - function as receptors for peptide hormones

Question 8

Definition of osmosis

Answer 8

The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)

Question 9

What are aquaporins?

Answer 9

Aquaporins are integral membrane proteins that form channels that allow for the passage of water molecules.

Question 10

What is facilitated diffusion?

Answer 10

Is the passive movement of molecules across a cell membrane via the aid of a membrane protein

Question 11

What are channel proteins?

Answer 11

Integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other
Channel proteins are ion-selective and may be gated to regulate the passage of ions in response to certain stimuli
Channel proteins only move molecules along a concentration gradient (i.e. are not used in active transport)
Channel proteins have a much faster rate of transport than carrier proteins

Question 12

What are carrier proteins?

Answer 12

Integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane
Carrier proteins will only bind a specific molecule via an attachment similar to an enzyme-substrate interaction
Carrier proteins may move molecules against concentration gradients in the presence of ATP (i.e. are used in active transport)
Carrier proteins have a much slower rate of transport than channel proteins (by an order of ~1,000 molecules per second

Question 13

Direct active transport

Answer 13

Is where the energy released by a reaction (like the breakdown of ATP) is used to directly transport

Question 14

Indirect active transport

Answer 14

Is where the movement of one solute down its concentration gradient drives the movement of the second solute against its concentration gradient.

Question 15

Selectivity in membrane permeability

Answer 15

Let some things through but not others, similar to diffusion

Question 16

Glycoproteins and glycolipids structure and function

Answer 16

Glycolaisation of a phospholipid results in a glycolic whiile glucoslation of a membrane protein produces a glycoprotein

Read book for functions

Question 17

Fluid-mosaic model

Answer 17

Must be able to draw

Question 18

Membrane fluidity

Answer 18

The membrane is “fluid” because the phospholipids can move around and switch positions within the bilayer

Question 19

Importance of membrane fluidity

Answer 19

Enables molecules to diffuse through the membrane to where they are needed in the cell.

Facilitate the interaction between proteins, which is crucial for cell signaling

Allows membranes to fuse with one another during the vesicle formation, endo and exocytosis

Ensures the even distribution of membrane molecules between daughter cells during cytokinesis

Question 20

How temperature affects membrane fluidity

Answer 20

Low temperature:
High viscosity
Densely packed
More rigid
Not permeable enough

High temperature:
More flexible
Less densely packed
Won’t hold shape
Too permeable

Question 21

Structure of cholesterol

Answer 21

Is a lipid
Hydroxyl group at one end
Four linked hydrocarbon rings
Hydrocarbon tail linked to the other end
Contains hydrophilic and hydrophobic parts making it amphipathic

Question 22

Function of cholesterol in the membrane

Answer 22

High temperatures - restrains the movement of the phospholipid fatty acids, stabilizing the membrane by making it less fluid and reducing its permeability to small molecules

Question 23

What is bulk transport in cells?

Answer 23

Vesicles can be used for bulk transport of many molecules into (endo) or out of (exo) the cell at once

Question 24

What is endocytosis?

Answer 24

The cell activity transports water and solutes into the cell by engulfing them into vesicles formed from the cell membrane

Question 25

Process of endoyctosis

Answer 25

Plasma membrane folds inward, creating a cavity filled with extracellular fluid, dissolved molecules, food particles, foreign matter, pathogens, etc

The membrane folds back on itself, trapping fluid inside the vesicle

The vesicle is pinched off from the membrane, moving into the cytoplasm

The cell membrane shrinks

Question 26

What is exocytosis?

Answer 26

The cell activity transports molecules out of the cell into the extracellular space.

Question 27

What is the process of exocytosis?

Answer 27

Vesicles containing molecules are transported from within the cell to the cell membrane

The vesicle membrane attaches to the cell membrane

Fusion of the membrane with the cell membrane releases the vesicle outside the cell

Cell membrane has grown larger

Question 28

What is a sodium potassium pump?

Answer 28

Sodium potassium pump proteins are integral proteins that generate an electrochemical gradient between the inside and outside of a nerve cell

They move 3 sodium ions out of the cell and 2 potassium ions into the cell using one ATP molecule to provide energy. The pumps are always moving against the concentration gradient via active transport

Question 29

Steps of sodium potassium pump

Answer 29

1. 3 sodium ions from inside the axon bind to the pump
2. ATP attaches to the pump and transfers a phosphate to the pump (phosphorylation) altering the pumps shape
3. The pump opens to the outside of the axon
4. The three sodium ions are released out of the axon
5. Two potassium ions from outside the axon bind to their sites
6. The phosphate is released, the pump shape and the potassium ions are released inside the axon

Question 30

Sodium-dependent glucose cotransporters as an example of indirect active transport

Answer 30

Glucose cotransport proteins, also known as glucose transporters, are essential in the small intestine and kidney nephron for efficient glucose absorption and reabsorption. In the small intestine they pump sodium ions out of the epithelial cells causing a concentration gradient that leads to sodium ions forming into cell from the lumen. They bring glucose molecules with them

Question 31

Multicellularity definition

Answer 31

Multicellular organism are composed of more than one cell that are adhered together. In a multicellular organism, the cells specialise and lose the ability to live independently

Multicellularity exist in:
All animals
All plants
Most fungi
Most algae

Question 32

What is a tissue and what are the 4 basic types?

Answer 32

Tissues are groups of cells in multicellular organisms that work together to perform a function, except blood, where cells must communicate to coordinate function.

4 basic types of tissue:

Connective tissue - binds and supports other tissues (bone)

Epithelial tissue - provides a covering (skin)

Muscle tissue - includes stirated muscles that move the skeleton (stomach)

Nerve tissue - made up of neurons. Carries electrical impulses to various places

Question 33

What are cell adhesion molecules (CAMs)

Answer 33

Proteins embedded in the plasma membrane, bind cells with other cells or extracellular matrix, aiding cell adhesion and different forms are utilised for different cell junction types.