CSF (week 3) Flashcards
cell SF, harvesting chemical energy, cell signalling
what is the endomembrane system
a network of membrane-bound organelles in a eukaryotic cell involved in many processes lie protein synthesis
what organelles are in the endomembrane system
nuclear envelope, endoplasmic reticulum, lysosomes and vesicles, and golgi apparatus
cytoplasm vs cytosol
cytoplasm is everything inside the cell excluding the nucleus, cytosol is the fluid portion inside the cell, consisting of water and dissolved/suspended substances
what is the plasma membrane
a selectively permeable barrier around the cell controlling the passage of substances in and out of the cell
describe the structure of the plasma membrane
fluid mosaic model, consisting of phospholipid bilayer with hydrophilic phosphate heads and internal hydrophobic lipid tails
2 important features of the PM
- dynamic (not static)
- cell specific (different proteins according to need)
6 functions/types of PM proteins
- transport
- enzymes
- cell signalling
- intercellular recognition
- intercellular joining (e.g cadherins)
- transmembrane (can perform many functions like above ones, can link cytoskeleton to ECM)
describe structure of the nucleus
- has a membrane; nuclear envelope
- nucleolus within the nucleus produces rRNA and ribosome sub-units
- has nuclear pores for entry/exit
explain the various forms of DNA and
double helix structure is wrapped around histones to form nucleosomes (8 histones in a nucleosome). chains of histones/nucleosomes form chromatin, which can organise itself into chromatin fibres, which condenses into chromosomes.
what are ribosomes made of and where
consist of small and large subunits made of rRNA and proteins. the subunits are made in the nucleolus and assembled in the cytoplasm.
what are the two sites of ribosomal protein synthesis, where do they end up, and why is this segregation important?
ribosomes can be in the RER or free in the cytoplasm. RER proteins are either used in the endomembrane system or are secreted, while ribosomes in the cytoplasm produce proteins which function in the cytosol.
separation allows for more efficient protein production, as proteins can be made right where they are intended to function.
when might DNA occupy various forms/structures
during interphase DNA usually exists as chromatin, but must be unwound during replication, and condenses to chromosomes during cell division.
function of the smooth ER
-storage for cell-specific proteins and enzymes (detoxifying enzymes in the liver)
-synthesis of lipids
stores calcium for muscle contraction in muscle cells
describe the structure and function of the golgi
consists of sacs called cisternae, usually 3-20 per apparatus. looks like a stack of pita breads.
proteins travel through the cisternae, receiving modification at each step, and maturing at the exit cisternae to travel via vesicles to their destination. movement occurs from the cis (ER facing side) to trans (extracellular facing side).
describe structure and function of lysosomes
lysosomes are vesicles formed from the golgi apparatus, contain powerful digestive enzymes. they digest old organelles and substances from outside the cell like pathogens. once a lysosome digests material, nutrient waste is released to be reused (e.g amino acids and lipids), and then the lysosome (containing the waste) leaves the cell via exocytosis.
what is it called when a lysosome digests its own cell’s organelles
autophagy
describe microfilaments structure, function, and features
7nm. made of actin molecules in two long, twisting chains. found around the periphery of the cell. dynamic - formed and reformed for different temporal requirements.
- bear tension and weight
- aid ameboid mobility.
describe ameboid motility
allows cell movement by rearrangement of the cytoskeleton
describe intermediate filaments structure, function, and features
8-12nm. composed of various substances, e,g keratin. found in the cytoplasm. more permanent, less dynamic.
- bear tension and weight.
- contribute to cell structure and organelle placement, like scaffolding.
describe the structure of an ATP molecule
adenosine associated with three phosphates
describe microtubules structure and functions
25nm outer diameter. consist of tubulin, both alpha and beta subtypes. 15nm inner diameter of tubular structure, with lumen inside. dynamic.
- support cell structure
- support movement of cell structures like cilia/flagellum
- are a ‘road’ for organelles, vesicles, and proteins.
- form the mitotic spindle for chromosome separation during cell division
3 main types of fuel for the body, and what they break down into
carbs; simple sugars
proteins; amino acids
fats; simple fats
describe glycolysis
first step of respiration; lysis of glucose. 6-carbon glucose chain is split into two 3-carbon pyruvate molecules, in the cytoplasm, in absence of oxygen.
glycolysis products and reactants
P: glucose
R: 2 pyruvate, 2 H2O, 2 ATP, 2 NADH
describe the significance of the 3rd step of glycolysis
phosphofructokinase enzyme catalyses the irreversible phosphorylation of fructose-6-phosphate -> fructose-1,6-biphosphate. this therefore the ‘gatekeeper’ and rate regulator for glycolysis. buildup of citrate and ATP will inhibit the enzyme, and buildup of AMP stimulates it.
why does AMP stimulate glycolysis rate?
because it signals low energy, as it means ATP is in high demand and is being used up
why do citrate and ATP inhibit glycolysis?
because citrate is a product of the CAC, implying that it is running smoothly. ATP presence means that energy levels are already high/available.
describe pyruvate oxidation
pyruvate enters the cell through transport protein to be converted to acetyl CoA by losing a carbon and binding to coenzyme A. this allows it to enter the CAC. occurs in the matrix, and requires oxygen.
reactants and products of pyruvate oxidation
R: 2 pyruvate
P: 2 CO2, 2 NADH, 2 acetyl CoA
describe the CAC
occurs in the mitochondrial matrix and requires oxygen. 2 acetyl CoA from pyruvate oxidation are invested, and 2 ATP, 2 FADH2, 4 CO2, and 6 NADH are produced.
reactants and products of CAC
R: acetyl CoA (2)
P: 2 ATP, 2 FADH2, 4 CO2, 6 NADH
why does the CAC require oxygen
because it requires acetyl CoA, which must be OXIDISED from pyruvate
what state are electron carriers in when they reach the ETC
reduced
what is an acetyl molecule
a 2 carbon molecule resulting from the loss of a carbon from pyruvate
what happens to NADH produced during glycolysis during aerobic and anaerobic conditions
oxygen present: sends its electrons via electron shuttles to the matrix, to be used in the ETC
oxygen absent: it is oxidised back to NAD+ to be reused in further glycolysis so ATP can be produced quickly without oxygen
define substrate phosphorylation
ATP production via transfer of a phosphate group from a substrate directly to ADP
where/when does substrate phosphorylation occur?
whenever ATP is produced in respiration prior to oxidative phosphorylation;
- during glycolysis in the cytoplasm
- CAC in the matrix,
reactants (what is needed) and products of oxidative phosphorylation
needed: reduced electron carriers, oxygen, H+, ADP + P
describe the ETC - detailed (i.e each complex.
NADH and FADH2 deposit electrons, which are transferred through a series of protein complexes in the inner membrane, simultaneously pumping H+ outside of the matrix to form an electrochemical gradient.
NADH transfers electrons at complex I, and FADH2 at complex II. Coenzyme Q transfers these directly to complex III, to cytochrome C, which transfers them to complex IV, which transfers them to oxygen, the final electron acceptor, which forms H2O.
what is cytochrome C
a small, mobile carrier protein transferring electrons between CIII and CIV
what complex in the ETC doesn’t pump H+ ions
complex II
explain chemiosmosis
H+ ions rush down the concentration gradient through the enzyme ATP synthase, which acts a turbine which the movement of H+ powers.
explain what is meant by the electrochemical gradient of H+
H+ creates a gradient of electrical charge due to its positive charge (greater in the inter membrane space where H+ has accumulated), and a chemical gradient due to the difference in H+ concentration between the intermembrane space and matrix
where are insulin and glucagon secreted
the pancreatic islets/islets of langerhaans.
- insulin; beta cells
- glucagon; alpha cells
what is the fasting blood sugar level that signals diabetes
7mmol/L or higher
what happens if we have no functional insulin?
we can’t take glucose into our cells, therefore blood accumulates too much glucose
what type of diabetic is insulin dependent
a type 1 diabetic, as they produce no insulin
examples of cellular activities as results of cell signalling
gene expression, alteration of protein function, regulation of cell’s metabolism, cytoskeleton rearrangement, regulation of cell’s organelles or organisation, open/closing of ion channel
explain the structure of a G-protein couples receptor (GPCR)
transmembrane that passes through the membrane 7 times. extracellular loop regions are hydrophilic, and embedded part is lipophilic.
what are G-proteins
proteins embedded in the cytoplasmic side of the membrane that act as molecular switches, becoming either active or inactive depending on whether GTP or GDP is bound to them (GDP=inactive)
explain how GPCRs work and are deactivated
a ligand binds to GPCR, causing a conformational change and activating it. it then binds to a G-protein, whose GDP will be replaced with GTP, activating it. the activated protein activates enzymes to carry out the cellular response. GTPase activity hydrolyses GTP back to GDP + P, reverting the G protein back to resting inactive state.
what system relies heavily on ligand-gated ion channels
nervous system
explain ligand-gated ion channel’s structure and function
transmembrane proteins with ligand-binding sites on the extracellular side. specific ligand binds, causing a conformational change resulting in the channel opening, allowing CERTAIN ions to enter down the concentration gradient. ligand dissociates and gate closes.
example of a neurotransmitter, and what else we may see it as
acetylcholine, is also a ligand for a gated ion channel.
4 main types of signalling
autocrine, paracrine, endocrine, synaptic
what is a protein ‘kinase’
a kinase phosphorylates (adds a phosphate from ATP) a molecule; a protein kinase phosphorylates a protein.
what dephosphorylates a protein
phosphatase enzymes
where would the receptor for a lipid-soluble messenger be found
not in the membrane. in cytoplasm, or nucleus.
what is the enzyme called in the GPCR activation that trigger
the GPCR/cAMP pathway is disrupted by:
cholera toxin
examples of lipid-soluble messengers
lipid-soluble hormones like oestrogen and testosterone, thyroid hormones, some gasses
3 main steps of cell signalling
reception, transduction, response
what are the two examples of things that are typically phosphorylated in the phosphorylation cascade
serine and threonine residues
finish sentence: activation usually _____ the start of _________
prompts, deactivation.
common second messengers
Ca2+, cAMP, IP3
what type of messengers are received by membrane-bound receptors
water-soluble ligands
how is cAMP activated
adenylyl cyclase is activated by G-protein, converting ATP to cyclic AMP- cAMP.
what does adrenaline do (in the signalling of the fleeing impala…)
acts as the messenger for a response resulting in breakdown of glycogen, releasing glucose for muscle use
how is glycogen broken down
glycogen phosphorylase converts glucose to glucose-1-phosphate, which can be converted to glucose-6-phosphate, which can be used in glycolysis for energy
what enzyme is associated with IP3 second messenger
phospholipase C
what does cAMP/other second messengers do
activate downstream proteins
what is a PP/phosphatase
enzymes that dephosphorylate proteins, removing a phosphate and rendering the protein inactive but reusable.
what does phospholipase C do
it is activated by G-protein (fills same place as adenylyl cyclase), and cleaves PIP2 phospholipid (in the membrane) into DAG and IP3 messengers.
what does IP3 do
diffuses through the cytoplasm to act as a ligand for a channel in the smooth endoplasmic reticulum, opening it and allowing Ca+ to flow OUT OF the SER down the conc. gradient.
where is Ca2+ found in high concentration, how is this maintained.
very high outside the cell, as well as in mitochondria and endoplasmic reticulum. maintained by calcium pumps.
why is it important that there are many steps in the cell signalling process
- each step amplifies the response significantly
- allows for temporal and spatial specificity of responses despite shared messengers
- provides multiple control points
- intermediates allow for coordination with other pathways
what breaks down cAMP - what details relate to it
PDE - caffeine halts its action
