eLFH - Cell Membrane characteristics and Receptors

Question 1

Structure of cell membrane

Answer 1

Fluid mosaic model
made up of phospholipids and proteins

Question 2

Thickness of cell membrane

Answer 2

7.5 nm thick

Question 3

Functions of the cell membrane

Answer 3

Separation of interior cell from external environment

Maintenance of concentration gradients and membrane potentials

Control movement in and out of cell

Maintenance of cell shape

Cell signalling

Question 4

Phospholipid components

Answer 4

Hydrophilic polar phosphate head - water soluble

Hydrophobic non-polar insoluble tails

Question 5

What holds phospholipids together

Answer 5

Van der Waals forces
Hydrogen bonds
Non-covalent interactions

Question 6

Types of membrane proteins

Answer 6

Integral
Surface
Transport
Enzymes
Receptors

Question 7

How are membrane surface proteins anchored

Answer 7

Glycosylphosphatidylinositol

Forms basis for antigens and cell adhesion molecules

Question 8

Modes of transport across cell membrane

Answer 8

Diffusion
Osmosis
Active transport
Endocytosis
Exocytosis

Question 9

Diffusion across cell membrane

Answer 9

Particles move down concentration gradient

Can be simple diffusion or facilitated diffusion

Question 10

Active transport across cell membrane

Answer 10

Movement of particles against concentration gradient
Requires energy

Question 11

Primary active transport

Answer 11

uses chemical energy of ATP (adenosine triphosphate)

Question 12

Secondary active transport

Answer 12

Uses an electrochemical gradient

Question 13

Endocytosis across cell membrane

Answer 13

Cells absorb molecules by engulfing them
Usually for large or polar molecules that cannot cross cell membrane in other ways

Question 14

Exocytosis across cell membrane

Answer 14

Method cells direct contents of excretory vesicles out of the cell

Question 15

Receptor definition

Answer 15

Molecules on surface of cells
Receive specific chemical signals from environment via ligands

When ligand binds to receptor, it induces or halts an intracellular activity

Question 16

Ligand definition

Answer 16

Peptides, neurotransmitters, hormones, drugs or toxins which bind to specific receptors to bring about a cellular response

Question 17

Types of receptor

Answer 17

Transmembrane proteins
Intracellular receptors
Peripheral membrane proteins - rare

Question 18

Example of transmembrane protein receptors

Answer 18

G protein or ligand-gated ion channels

Question 19

Example of intracellular receptors

Answer 19

Hormone receptors

Question 20

Example of peripheral membrane proteins

Answer 20

Elastin

Question 21

G protein coupled receptors

Answer 21

Seven transmembrane domains
Enzyme linked receptors
Effects are on Guanosine triphosphate (GTP) proteins

Question 22

Two main signal transduction pathways for G protein coupled receptors

Answer 22

cAMP

Phosphatidylinositol

Question 23

Examples of G protein coupled receptors

Answer 23

Muscarinic acetylcholine receptors
Adrenoreceptors
Histamine receptors

Question 24

Activation of G protein coupled receptors

Answer 24

Ligand binding to extracellular portion of receptor

Conformational change allows GDP to exchange for GTP on the G-alpha subunit

This causes dissociation of the subunits into a G-alpha-GTP complex and a G-beta-gamma complex

G-alpha-GTP complex acts on effector organs or ion channels to modulate cellular processes

Question 25

Deactivation of G protein coupled receptors

Answer 25

GTPase exchanges GTP back for GDP on G-alpha subunit

This deactivates it and causes re-association of all receptor subunits (G-alpha-beta-gamma-GDP complex)

Subunit complex re-binds to seven transmembrane receptor on intracellular portion

Question 26

Tyrosine kinase receptors

Answer 26

Receptor for many polypeptides including hormones and growth factors

E.g Insulin and Erythropoietin

Question 27

Structure of tyrosine kinase receptors

Answer 27

Extracellular N terminal with ligand biding site

Intracellular C terminal which is responsible for kinase activity

Question 28

Kinase enzymes function

Answer 28

Phosphorylation

Question 29

Tyrosine kinase receptor pathway

Answer 29

Receptor binding leads to phosphorylation of tyrosine

Activates signal transduction pathways

Alters cellular activity

Question 30

Ionotropic receptors definition

Answer 30

Ligand gated ion channels

Open and close in response to ligand binding

Question 31

Allosteric binding definition

Answer 31

Binding site for ligand is on a different part of the protein to the ion channel

Question 32

Examples of ionotropic receptors

Answer 32

Nicotinic acetylcholine receptors

NMDA glutamate receptor (N-Methyl-D-Aspartic acid)

GABA receptor (Gamma-aminobutyric acid)

Question 33

Nicotinic acetylcholine receptor structure in adults

Answer 33

Ligand gated ion channel

5 subunits:
- 2x alpha units
- beta unit
- delta unit
- epsilon unit

Question 34

Foetal nicotinic acetylcholine receptor structure

Answer 34

5 subunits:
- 2x alpha units
- beta unit
- 2x delta unit

(I.e extra delta instead of epsilon subunit that adults have)

Question 35

Nicotinic acetylcholine receptor activation

Answer 35

2 acetylcholine molecules binds to both alpha subunits

Conformational change opens the ion channel

Na+ moves into cell down concentration gradient
K+ moves out of cell down concentration gradient

Question 36

Intracellular receptors ligand binding

Answer 36

Receptors are intracellular

Ligands that bind them either secondary messengers or lipophilic hormones that can pass through cell membrane

Question 37

Examples of ligands which use intracellular receptors

Answer 37

Nuclear receptors that bind oestrogen and thyroid hormones

Vitamin D receptors

IP3 receptor on endoplasmic reticulum

Question 38

Types of drug receptor interaction

Answer 38

Full agonist
Partial agonist
Inverse agonist
Competitive antagonist
Non-competitive antagonist

Question 39

Full agonist definition

Answer 39

Drug induces a receptor’s maximal response

Question 40

Partial agonist definition

Answer 40

Drug induces a submaximal receptor response

Question 41

Inverse agonist definition

Answer 41

Drug induces opposite effect than the intrinsic agonist

Question 42

Competitive antagonist definition

Answer 42

Drug competes with the intrinsic agonist for the receptor and blocks its activity

Question 43

Non-competitive antagonist

Answer 43

Drug binds to a different site to the intrinsic agonist and prevents receptor activation