Membreme

Question 1

Amphipathic

Answer 1

Comprising hydrophilic and hydrophobicregions

Question 2

Three major till type of membrane lipid?

Answer 2

Glycerophospholipids
Sphingolipids
Sterols

Question 3

Glycerophospholipids

Answer 3

Phosphorylated head group
Three-carbon glycerol backbone and hydrocarbon fatty acid chain
-M group include, choline or serine
Amphopathic various derivatives present in varying amounts in membrane of all cell
Fatty acid tail can be saturated or unsaturated cone or more double bond

Question 4

Sphingolipids

Answer 4

Phosphorylated head group•
Sphigosine backbone and 2 hydrocarbon fatty acid chairs one of the latter acid chains is’ he sphingosine
Polar group includes choline or can be a sugar
Amphipathic a present in most cellsbut most abundant in myelin sheath surrounding nerve cells

Question 5

Sterols

Answer 5

Cholesterol in animals(ergosterol in fungi, hoponoid, in bacteria)
Present in varying amounts and influences membrane in varying amounts and influences membrane fluidity rigidity
Unsaturated, double bonds in fatty acid tails create space to s terol to sit in the membrane

Question 6

Composed n and properties of membrane

Answer 6

The outer and inner layers can have different compositions
Clustering of lipid molecules to give domains or rafts
Different cells and organelles can have different membrane compositions also can be single bi layer or double bilayer the study of a membrane
Membranes are self-sealing- ensuresthe cell remains intact and not damaged of killed
Key processes like cell division,endobutosis) exocytosis
Selectively permeable
Separating the inside environment of the cell
From the out side

Maintenance of pH and ionic composition
Regulation of cell volume
Concentration of metabolites and extrusion of waste substances and toxin
Generation of ion gradients for excitable tissues (muscle and nerve )

Question 7

Channel/ cores/transporters

Answer 7

Allow compounds to enter or leave thecell either
Along their concentration passive transport 1 diffusion lfacilitated diffusion by
By extending energy to move against their concentration gradient - active transport
Are integral membrane protein and require several polypeptide subunits arranged to creat a structure with central equal us channel
Allow movement of molecules across the membrane and controlled by opening or closing by the subunits

Question 8

Receptors and adesión molecules

Answer 8

Bind extracellular molecules without necessarily transporting across the membrane
Allow cells to sense their environment and to adhere to their tissue
Many other prodien and enzyme are present in /on membrane

Question 9

Selective permanbily

Answer 9

Water, gaser(O2, CO 2, No) - urea compass through the belayer unaided
Rate of movement of water might not be sufficient for cell function
Gases dirt use rapidly due to concentration gradient
Although water passes throughfacilitated transport by (aqua) poring is required
Ion sugar amino acid can not pass through the membrane unaided and require integral membrane protein do
Passive transport - diffusioni facilitated diffuse
Active transport requiring expenditure of energy

Question 10

Transport be diffusion is driven by difference on either side of the melane can be

Answer 10

Chemical electrical

Question 11

Diffusion process is influenced by what

Answer 11

Steepness of the concentration gradient
Temperature
Size or mass of diffusing substance
Surface area
Diffusion distance
Numbers of channels/transporters on the surface of the cell

Question 12

How transporters help

Answer 12

Allow accumulation against a concentration gradient
Higher specific for one molecule ion or class or molecules sugars amino acid
Require expenditure- energy and there are several key sources
ATP hydrolysis
Dissipation of proton/ sodium gradient

Question 13

Examples of transports

Answer 13

Uniporters, symporters, antiporters (involve ATP hydrolysis; secondary proton or sodium gradients)
ATP-binding cassette (ABC) system (ATP hydrolysis)

Question 14

Transporters (active)

Answer 14

Transporters move compounds in and out of cells against their concentration gradients

This requires energy, which can be supplied by ATP hydrolysis (ATPases) e.g.,
Sodium-potassium pump, calcium pump
Mitochondrial ATP synthase
ATP- Binding Cassette (ABC transporters)

Question 15

Secondary active transport

Answer 15

Secondary active transport / co-transport of a molecule along its concentration gradient (co-transporters); uses energy of ATP hydrolysis indirectly to establish proton or sodium gradients
e.g., Na+ – K+ ATPase or Na+ pump is a membrane transporter that maintains gradients of Na+ and K+ across the membrane.
For each ATP hydrolyzed 3 Na+ ions are removed from the cell and 2 K+ are brought in; by keeping this Na+ gradient, it creates a secondary ‘energy’ source to drive secondary active transport

Proton gradients are also used to drive activity of mitochondrial ATP synthase and generation of ATP

Question 16

Channels?

Answer 16

Channels, carriers (facilitated) allow diffusion of specific molecules down a gradient

Gated ion channels are highly selective for specific ions and open and close in response to a particular signal
ligand-gated (e.g., acetylcholine binding its receptor – see figure below)
voltage gated (e.g., potential difference across a membrane – depolarization)

Gap junctions are channels that connect directly with neighbouring cells
Prominent in cells like cardiomyocytes where there is rapid communication and movement of ions across the heart to mediate contractile forces

Question 17

The atp-binding cassette (ABC) tranpotter

Answer 17

Over 200 different ABC systems

Present in pro- and eukaryotic cells

Transport best studied in Gram negative bacteria

In human cells ABC transporters are involved in;
Cystic fibrosis (Cystic Fibrosis Transmembrane Conductance Receptor - CFTR) – is a Cl- transporter, that is mutated in conditions like CF
Multi-drug resistance – pumping drugs out of a cell, notably cancer cells

Requires energy generated by hydrolysis of ATP – active transport

Question 18

Receptors?

Answer 18

Most receptors bind extracellular molecules without transporting them across the membrane and allow cells to sense their environment

Receptors detect extracellular signals, called ligands such as hormones and growth factors or molecules

Most receptor ligands do not move across the membrane, but cause a change in the cytoplasmic domain of the receptor protein, either through clustering of the receptors or through inducing a conformational change of the receptor protein

They usually initiate a cascade of signalling molecules – second messengers such as cAMP or cGMP – see pharmacology lectures

Question 19

What are main principles of passive and active transport

Question 20

Outline the processes of active and secondary active transport

Question 21

Exocytosis

Answer 21

Exocytosis; secretion of proteins out, across the cytoplasmic membrane
Packaged into secretory vesicles by Golgi apparatus and targeted to cytoplasmic membrane;
Vesicles fuse with cytoplasmic membrane and release their contents extracellularly; may involve clathrin-coated pits (see endocytosis)
Constitutive and active processes
Bacteria have dedicated transporter systems called translocases; constraints of the cell wall means exocytosis, endocytosis etc might be as possible compared to animal cells

Question 22

Endocytosis

Answer 22

Endocytosis; Uptake of macromolecules from extra-cellular space, across the cytoplasmic membrane; occurs continuously in all animal cells

Question 23

Pinoctosis

Answer 23

Pinocytosis is a constitutive and continuous process involving uptake of extra-cellular fluid via small membrane vesicles

Question 24

Phagocytosis

Answer 24

is a specialized form of endocytosis in macrophages and neutrophils to ingest bacteria and cell debris

Question 25

Receptor mediated endocytos is

Answer 25

involves the protein clathrin forming clathrin-coated pits and vesicles; protein has a distinctive 3-legged structure called a triskelion, which assemble to form a basket-like structure to stabilize the endocytic vesicle; uptake of cholesterol most studied process

Question 26

Key facet of cell function

Answer 26

Signaling

Question 27

To able the drag interact membrane

Answer 27

Drugs must also ‘negotiate’ the cell membrane and need to interact with and follow the various membrane transport and signalling mechanisms and principles

Question 28

Agonists

Answer 28

activate the target as a ligand e.g., Insulin

Question 29

Antagonists

Answer 29

block the activation of the target by ligand e.g., Beta blockers block the adrenaline receptor (treating hypertension and arrhythmia)

Question 30

Signal transduction blockers

Answer 30

Kinase inhibitors are being developed as cancer treatments