Cells and other smaller lectures Flashcards
Are all cells enclosed by a membrane ?
YES
What three systems do most eukaroyotic organelles belong to ?
Protein Uptake
Secretion Pathway
Uptake and degradation
What are the main differences between euchromatin and heterochromatin ?
Euchromatin is less intensely stained and contains most active genes.
Where does protein synthesis occur ?
In ribosomes present in the cytosol (the ribosome then either stay in the cytosol or bind to ER)
Where are ribosomes assembled ?
In nucleolus at amplified ribosomes genes.
What is the difference between constitutive and secretory vesicles ?
Constitutive bud from Golgi with membrane
Secretory bud from Golgi with packaged secretion
What are the models of Golgi transport ?
Cargo moves forward from sac to next through vesicles (stable Golgi sacs)
Factories move with cargo and recycle in vesicles (maturing Golgi sacs)
What is one reason for Golgi being close to the microtubule tracks ?
Upon secretion from Golgi, vesicles are transported along polarised microtubules track emanating from centrosomes (=MOC)
What is the relation between centrosomes and centrioles ?
In animal cells, 2 centrioles per centrosome
What is the process of uptake and degradation in cells ?
Following endocytosis of material and delivery to endosomes, it is passed on to lysosomes for degradation using low pH and hydrolytic enzymes.
What is autophagy ?
Cytoplasmic components digested in lysosomes.
What is pinocytosis ?
Fluid intake
What is receptor-mediated endocytosis ?
Absorption of protein/virus by inward budding of membrane vesicle containing proteins with receptor for the protein/virus
Where are the functional components of endosomes and lysosomes made ?
RER
How does protein degradation by proteasome work ?
Junk protein tagged with ubiquitin (in cytoplasm, not lysosome).
Proteasome detects it and degrade protein through proteolysis
What are the two great steps in eukaryotic cell evolution ?
Compartmentation
Mitochondria
What is clathrin ?
Scaffold coat aiding vesicle budding
What are the differences between microtubules, intermediate filaments and microfilaments?
Microtubules: thickest. Vesicle track made of tubulin
Microfilaments: thinnest. Generates contractile forces enabling movement and contraction. Made of actin
Intermediate filaments: middle thickness. Helps with strength and support (some in cytoplasm, others support nuclear envelope. Laminin, keratin)
What is the role of the SER ?
Lipid, steroid production and detoxification
What is the role of peroxisomes ?
Breaks down FAs, synthesise specialised lipids and so oxidative reactions using molecular oxygen.
What is the aim of cell replication ?
Condensing chromosomes.
What is the name of the OG cell ?
Totipotent stem cell
What are the stages following totipotent stem cell ?
Totipotent stem cell –> Blastocyst with pluripotent SCs –> Isolated pluripotent SCs + Lematopoietic SCs (lead to blood cells) + neural SCs + mesenchymal SCs (lead to CT)
What is hypercholesteroleamia due to ?
Defective uptake of lipoprotein. May be due to:
1) LDL not properly transported from RER to Golgi for expression on cell surface
2) LDL receptor bound to LDL does NOT cluster in endocytic vesicles on plasma membrane
3) LDL not recycled back to cell surface
What is cystic fibrosis due to ?
Misfolding of protein.
What is tertiary structure ?
3D of secondary structure as a result of bonds (hydrophobic, Van der Waals, ionic, disulfide bridge, H-bonds)
What is the role of loops/bends as part of the tertiary structure ?
Linking regions of alpha helix and beta sheet.
What is quaternary structure?
Association of more than 1 polypeptide to form oligomeric functional protein
What is the structure of haemoglobin ?
2 alpha globins and 2 beta globins. Each globin has a haem which transport O2.
What is the structure of haem and how does the binding of oxygen change it?
Porphyrin ring with coordinate iron atom.
Haem molecule held in placed by H-bonds from histidine F8
Bound O2 molecule stabilised by histidine E7
O2 binding causes haem to go from non-planar to planar.
What kind of curve is the O2 binding curve of haemoglobin ?
It is a cooperative binding curve. Affinity of first oxygen molecules is low but binding of subsequent oxygen molecules increases this affinity
As O2 binds, histidine F8 which H-bonds to Haem molecule changes position which causes major structural changes in the globin subunit.
What is the mutation occurring in sickle cell anaemia and what is the result of this mutation ?
Hydrophilic glutamic acid to hydrophobic valine (single AA change at position 6 in beta chain of haemoglobin)
Causes sickling of RBCs due to aggregation of mutated haemoglobin forming stuff fibres
What is the effect of pH concentration on haemoglobin ? How does this relate to exercice ?
Bohr effect, O2 binding occurs with higher affinity (lungs) at high pH and lower affinity at lower pH (peripheral tissues).
In exercice, CO2 builds up which lowers blood pH which facilitates O2 delivery
What is the difference in structure of RBCs in fetal blood ? Why is this significant ?
2 gamma subunits instead of beta subunits. Fetal haemoglobin binds O2 with greater affinity (necessary since blood less rich in O2 by time it reaches placenta)
Which are glycine and proline important in collagen formation ? What is hydroxyproline and why is it important in collagen formation ?
Glycine allows for tight turns in tropocollagen triple helix.
Proline (faces outwards) imposes L hand twist in helix, provides stabilising force.
Hydroxyproline (faces outwards) is a hydroxylated form of proline. Forms strong hydrogen bonds which helps stabilise the triple helix.
What are the components of the cross-links between tropocollagen molecules ? How do they achieve these cross-links ?
Lysine-derived aldehydes called lysyl oxidases.
What is the AA mutation leading to osteogenesis imperfecta ? What is the result of this ?
Glycine replaced by cysteine which is bulkier (in gene coding for one of collagen subunits).
Tropocollagen subunits cannot pack properly, knock on effect on collagen fibre formation.
What are the symptoms of scurvy and what is its structural cause ?
Dry skin, gum disorders.
Lack of hydroxyproline (due to vitamin C deficiency)
What are the symptoms of Ehlers-Danloss syndrome and what is its structural cause ?
Loose skin, hypermobile joints.
Lock of procollagen peptidase (form mature procollagen) or lysyl oxidase (no cross-links)
What is rate enhancement ?
Catalysed rate / Uncatalysed rate
What is a non-enzymatic half life ?
For half of the reactans to convert to product without enzyme.
What is the half life of an enzyme ?
TIme for activity to reduce to half of original activity.
Why is the product accumulation of an enzymatic reaction not linear ?
The concentration of substrate falls, the product may inhibit the enzyme, the enzyme may denature, reverse reaction may become more favourable.
What is the only valid parameter when measuring enzyme activity ?
Initial reaction velocity
What is Vmax ?
The maximum velocity of a reaction. Rate of reaction increases as substrate concentration increases until Vmax is reached.
Why is a double reciprocal of the data used when graphing enzymatic reactions ?
Because Vmax is very hard to actually achieve
What are the axes of enzymatic graphs ?
X axis: 1/V0 (second/micromolar)
Y axis: 1/[S]
What is the equation of this line ? What are the intercepts of this ?
I/V0 = (Km/Vmax) I/[S] + I/Vmax
X-intercept is -I/Km
Y intercept is I/Vmax
What is Km ?
The substrate concentration required for half of the maximum velocity.
What is the biological importance of Km?
Hexokinase is found in all tissues. It has a low Km which means it ensures utilisation of glucose even at very low concentrations.
Glucokinase is found in liver. Ensure glucose is not removed from blood for storage at low concentrations.
What are the different kinds of enzymes?
Irreversible (inactivators) and reversible (allosteric and non-competitive)
What are examples of irreversible inhibition ?
- Organophosphates (pesticide). Phosphorylates hydroxyl group at active site of AChE. Hence they are inactivated and accumulate in nervous system, resulting in overstimulation and death.
- Aspirin (acetylsalicylic acid). Reacts with serine residue close to active site which prevents arachidonic acid from binding.
What is an example of reversible, competitive inhibition ?
Sulphonamides- similar in structure to 4-aminobenzoic acid which is essential for bacteria.
How do competitive inhibitors alter the kinetics ?
Higher concentration of substrated needed to reach Vmax so increase in Km (Vmax is unchanged).
Hence -1/Km increases as well.
How do allosteric inhibitors alter the kinetics ?
- mixed allosteric: Affects both activity and binding. Vmax decreases and Km increases
- non-competitive: Affects activity but not binding. Substrate affinity (Km) does not change but Vmax is reduced.
What is an example of allosteric inhibition ?
Phosphofructokinase catalaysed transfer of phosphate from ATP to fructo-6-phosphate by binding at 2 sides.
In presence if high levels of ATP, inhibitory site is occupied.
As a result, glycolysis does not proceed when ATP not needed.
What are the 6 types of enzyme reaction (give example of enzyme for each) ?
Hydrolases (trypsin) Oxidoreductatses (alcohol dehydrogenase) Lyases (carbonic anhydrase) Isomerases (L-alanine isomerase, mutases) Transferases (hexokinase) Ligases (Carboxylases)
What are co-factors ?
Substance whose presence is essential for the action of an enzyme
What are the types of co-factors ?
- Prosthetic groups (integral part of enzyme structure, like HAEM)
- Cofactor acting as an acceptor for an atom removed from the substrate
What is a co-enzymes ? Give an example
A co-factor acting as an acceptor for an atom removed from the substrate when it is promiscuous, consorting with more than 1 enzyme e.g. donates atom in reaction catalysed by different enzyme)
E.g NAD in catabolism of glucose and FAs
Can we synthesise most of our co-enzymes ?
No, get them in our diet in the form of vitamins
Which of these has a higher concentration inside the cell and which has a higher concetration extracellularly ?
K+ Na+, Ca++, Cl-
K+
Na+, Ca++, Cl-
How are FAs stored ?
Through ester linkage to glycerol, forming triacyl glycerols.
What is the structure of a steroid ?
4 fused carbon rings with functional groups attached.
What are some uses of AAs (other than forming proteins) ?
Neurotransmitters (glutamine)
Sources of energy
Precursors for other molecules (glycine for porphyrin ring)
What are some functions of nucleotides ?
- ATP and GTP are good energy stores (Because the link between the second and third phosphate high in energy )
- NADP and NADPH are good e- store (e.g. for ATP reduction)
- Cofactors for enzymes (coenzyme A)
- Signalling molecules (cAMP)
- Building blocks for nucleic acids
What structures are lost in denaturation ?
Secondary, tertiary and quaternary
Which molecules can be recognised and targeted vaccines ?
Glycoproteins
What are examples of diseases caused by protein misfolding and aggregation ?
Alzheimer's Parkinsons's Prion Diabetes type 2 Huntington's
What do D and L indicate in aldose/ketose nomenclature ?
How atom organised in way most similar to glyceralderhyde (chiral C farthest from carbonyl determines L or D. L if left D if right)
Which organic molecules are known for always being in L configuration ? in D configuration ?
AAs always in L
Sugars always in D
What are epimers ?
Either of two stereoisomers that differ in the arrangement of groups on a single asymmetric carbon atom
What is galactosaemia ?
Lack of enzymes to metabolise galactose. Toxic effects in liver, brain, kidneys.
What are anomers ?
Cyclic monosaccharides or glycosides that are epimers, differing from each other in the configuration of C-1 if they are aldoses or in the configuration at C-2 if they are ketoses (switch from beta configuration to alpha configuration)
What test is there for reducing sugars ?
Fehling’s reagent, attempts to convert Cu2+ to Cu+ (blue to colorless)
What is the difference between glucose oxidase test and glycation ?
Glucose oxidase test only gives short term insight into sugar control.
Glycation tells us about glucose levels in past months using RBCs (involves looking at HbA1C. If too high, may be diabetic.)
What is lactose ?
Disaccharide with: 1. beta-D-galactose and 2. alpha or beta-D-glucose
beta 1-4 glycosidic bonds
What is glycogen ?
Highly branched polysaccharide. Glucose units with
alpha 1-4 glycosidic bonds and alpha 1-6 glycosidic bonds
What is starch ?
Plant form of carbs.
Two forms:
amylose (unbranched, 1-4 alpha bonds, 20%)
Amylopctin (beanched, 1-4 and 1-6 alpha bonds, 80%)
What is cellulose ?
Storage in plants.
1, 4 beta bonds.
What is the Handy Weinberg principle ?
relative proportions of genotypes constant throughout generations. NOT ALWAYS TRUE
4 duties of a Dr ?
Knowledge, skill and performence
Safety and quality
Communication, parternship and teamwork
Maintaining Trust
