membranes

Question 1

amphipathic

Answer 1

comprising hydrophilic and hydrophobic regions

Question 2

what are the three sorts of membranes

Answer 2

-Glycerophospholipids
-Sphingolipids
-Sterols

Question 3

Glycerophospholipids

Answer 3

-Phosphorylated head group, three-carbon glycerol backbone and 2 hydrocarbon fatty acid chains

-Amphipathic, various derivatives present in varying amounts in membranes of all cell

-Fatty acid tail can be saturated or unsaturated (one or more double bonds – creates ‘kinks’ in the tail)

Question 4

Sphingolipids

Answer 4

-Phosphorylated head group, sphingosine backbone and 2 hydrocarbon fatty acid chains

-Amphipathic, present in most cells, but most abundant in myelin sheath surrounding nerve cells

Question 5

Sterols

Answer 5

-Cholesterol in animals (ergosterol in fungi, hoponoids in bacteria)

-Present in varying amounts and influences membrane fluidity/rigidity

-Unsaturated, double bonds in fatty acid tails create space for sterols to sit in the membrane

Question 6

lipids and rafts

Answer 6

Within the membrane, certain lipid molecules can cluster together to form specialized regions called lipid rafts or domains. These are patches where specific lipids, proteins, and cholesterol are concentrated. These regions are more ordered and thicker than the surrounding membrane, helping organize the membrane’s structure.

The lipid rafts play an important role in cell signaling and transport. For example, they can help concentrate receptors and signaling molecules in one area, facilitating faster or more efficient communication between the cell’s exterior and interior. Additionally, these rafts can assist in the transport of materials across the membrane by forming vesicles or helping in the sorting of proteins and lipid

Question 7

Composition influences…

Answer 7

the thickness, curvature and the lateral freedom of movement of lipids in the bilayer; the fluidity of a membrane

Question 8

why are membranes being self sealing important

Answer 8

Key for processes like cell division, endocytosis and exocytosis

Question 9

membranes being semi permeable barries that separate the inside environment from the outside is important because

Answer 9

-Maintenance of pH and ionic composition

-Regulation of cell volume

-Concentration of metabolites and extrusion of waste substances and toxins

-Generation of ion gradients for excitable tissues (muscle and nerve)

Question 10

membrane proteins: channels/pores/transporters

Answer 10

allow compounds to enter or leave the cell either;
Along their concentration gradients – passive transport / diffusion / facilitated diffusion, or;
By expending energy to move against their concentration gradients – active transport

Question 11

membrane proteins: Receptors and adhesion molecules

Answer 11

bind extracellular molecules without necessarily transporting them across the membrane and allow cells to sense their environment and to adhere to their tissue

Question 12

other membrane proteins

Answer 12

Many other proteins including enzymes and immune system molecules are present on/in the membrane

Question 13

what can pass through the bilayer

Answer 13

-water: not enough for cell function so aqua porins are required
-gases diffuse down the conc gradient
-urea

Question 14

cannot pass through the membrane unaided

Answer 14

-Ions, sugars, amino acids

-channels and transporters control passive transport and active transport

Question 15

Transport by diffusion is driven by differences on either side of the membrane and can be;

Answer 15

Chemical

Electrical

Diffusion process is influenced by;
Steepness of the concentration gradient

Temperature

Size or mass of the diffusing substance

Surface area

Diffusion distance

Question 16

active transport proteins

Answer 16

-most of the substances a cell needs to survive are low in natural environments
-so transporters allow accumulation against the concentration gradient

-Usually highly specific for one molecule

-Integral membrane proteins

-Require expenditure of energy and there are several key sources e.g.,
ATP hydrolysis
Dissipation of proton /sodium gradient

Question 17

channel proteins

Answer 17

-allow compounds to enter or leave the cell along their concentration gradients

-can have gated ion channels which only open with specific ions. eg. ligand-gated (e.g., acetylcholine binding its receptor)
voltage gated (e.g., potential difference across a membrane – depolarization)

Question 18

bacteria involvement with channel proteins

Answer 18

Some bacterial toxins insert into cell membranes, creating pores / mimicking channels or pores and cause net leakage of water and ions and cause cell death

Question 19

gap junction

Answer 19

type of Chanel protein 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 20

atp for active transporters can come from

Answer 20

Sodium-potassium pump, calcium pump
Mitochondrial ATP synthase
ATP- Binding Cassette (ABC transporters)

Question 21

symport

Answer 21

are co-transporters that transfer both molecules in the same direction

Question 22

Antiport

Answer 22

are co-transporters that transfer molecules in opposite directions

Question 23

The ATP-Binding Cassette (ABC) transporter (membrane protein example)

Answer 23

-Over 200 different ABC systems

Present in pro- and eukaryotic cells

-ABC transporters are active transporters, meaning they require energy to move substances across the membrane against their concentration gradients. This energy comes from the hydrolysis of ATP, which provides the power to drive the transport process.

Question 24

examples on ABC in humans

Answer 24

Cystic Fibrosis Transmembrane Conductance Regulator (CFTR): In humans, one important ABC transporter is the CFTR, which acts as a chloride (Cl⁻) ion channel. In cystic fibrosis, mutations in the CFTR gene prevent it from functioning properly, leading to thick mucus in the lungs and other symptoms.

Multi-drug resistance (MDR): ABC transporters also play a role in multi-drug resistance (MDR), particularly in cancer cells. In this case, ABC transporters like P-glycoprotein pump chemotherapy drugs out of the cells, making the cancer cells resistant to treatment.

Question 25

ABC in gram negative bacteria

Answer 25

ABC transport system involves mobile periplasmic binding proteins that have a high affinity for specific substrates. These proteins bind the substrate outside the cell, and the energy from ATP is used to transport the substrate across the bacterial membrane into the cell.

Question 26

receptors

Answer 26

-bind to extracellular molecules without transporting them inside -receptors detect extracellular signals, called ligands such as hormones, growth factors or molecules -When the ligand binds to the extracellular part of the receptor (the part facing outside the cell), it causes a change in the cytoplasmic domain (the part of the receptor inside the cell). This change can initiate a variety of intracellular signaling pathways that lead to a cellular response, like gene expression, metabolism changes, or cell movement. or can cause clustering to make signal stronger. ligand causes the receptor to undergo a conformational change, meaning it changes shape. This change is often critical because it activates the receptor, allowing it to interact with other proteins inside the cell and start the signaling process. -They usually initiate a cascade of signalling molecules – second messengers such as cAMP or cGMP – see pharmacology lectures

Question 27

Secondary active transport

Answer 27

secondary active transport uses the energy stored in ion gradients (created by primary active transport) to move other molecules against their concentration gradient. Unlike primary active transport, it does not directly use ATP but relies on the ion gradients maintained by primary active transport systems.

Question 28

release of macromolecules, particles or ‘foreign bodies’ in cells

Answer 28

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

Question 29

bacteria endocytosis and exocytosis

Answer 29

Bacteria have dedicated transporter systems called translocases; constraints of the cell wall means exocytosis, endocytosis etc is not as possible

Question 30

uptake of macromolecules, particles or ‘foreign bodies’

Answer 30

Endocytosis; Uptake of macromolecules from extra-cellular space, across the cytoplasmic membrane; occurs continuously in all animal cells Small portion of cytoplasmic membrane envelopes the molecule, invaginates and pinches off as an intra-cellular vesicle -Clathrin-mediated endocytosis involves receptor proteins on the cell surface that bind specific ligands (such as cholesterol) and trigger the formation of clathrin-coated pits. Clathrin proteins assemble into a triskelion structure 3 legged, which forms a basket-like coat around the vesicle

Question 31

Phagocytosis

Answer 31

is a specialized form of endocytosis in macrophages and neutrophils to ingest bacteria and cell debris Pinocytosis is a constitutive and continuous process involving uptake of extra-cellular fluid via small membrane vesicles

Question 32

agonistis and antagonists

Answer 32

These are drugs that act on receptors or ion channels on the cell membrane, which are essential for cell communication and signal transmission. another way of drugs work is targeting signal transduction molecule (but that is a diff flash card)

Question 33

Agonists

Answer 33

Agonists are molecules that activate a receptor or channel, mimicking the action of the natural ligand (the molecule that normally binds to the receptor). They bind to the receptor and trigger a response in the cell, just as the natural ligand would. Example: Insulin is an agonist for the insulin receptor. It binds to the insulin receptor on target cells (like muscle and liver cells) to activate glucose uptake and metabolism.

Question 34

Antagonists

Answer 34

Antagonists are molecules that block the receptor or channel from being activated by its natural ligand. Instead of triggering the receptor, they prevent any response. These drugs can be used to inhibit excessive signaling, often by preventing the activation of receptors by endogenous molecules (like hormones or neurotransmitters). Example: Beta blockers are antagonists that block the adrenaline receptors (beta-adrenergic receptors). By preventing adrenaline from binding to these receptors, they help lower blood pressure, making them useful in treating hypertension and arrhythmias (irregular heart rhythms).

Question 35

Signal transduction

Answer 35

refers to the process by which a cell responds to external signals (like hormones or growth factors) through a series of molecular events inside the cell. These signals often activate kinases, which are enzymes that modify other proteins to propagate the signal.

Question 36

Signal transduction blocker

Answer 36

Kinase inhibitors are drugs that block specific kinases involved in signal transduction pathways. These enzymes often play a key role in regulating cell growth, division, and survival. Many cancers are driven by dysregulated signaling, where kinases become overactive, leading to uncontrolled cell growth. Kinase inhibitors are being developed to target these overactive kinases, thereby treating cancer and other diseases driven by abnormal signal transduction.

Question 37

Adhesion molecule

Answer 37

allow cells to sense their environment, stick together to form tissues and adhere to extracellular matrix – Cadherins and Integrins