MCGB Revision Lecture 1b Flashcards
DNA replication is
sem-conservative
DNA replication is a 3 stage process
- initiation
- elongation
- termination
in DNA replication the chain grows in a
5’ to 3’ direction
what drives DNA replication
pyrophosphate hydrolysis
outline DNA replication
1) Topoisomerase unwinds the DNA and Helicase breaks the hydrogen bonds between the parental double helix
2) DNA primase synthesises RNA primers, which allow DNA polymerase to bind to single strand
3) Leading strands is read in the 3’ to 5’ direction and synthesised continuously in the 5’ to 3’ direction by DNA polymerase
4) Lagging trans is synthesised discontinuously- primase synthesises numerous short primers which are extended by polymerase to form Okazaki fragments
5) After the primer is replaced by DNA, DNA ligase joins the Okazaki fragments
termination of DNA replication occurs when
two facing repclication forks meet and DNA ligase joins the final frgaments
telomeres
repetitive DNA sequences that protect the integrity of chromsosmes
- prevents degradation of coding material
- ensure genomic stability
telomerase
prevents telomeres shortening
- -> when there is not enough DNA for primers (oligonucleotides) to bind to = uneven length of both strand s of DNA= degradation of longer strand
- -> telomerase lengthens the DNA so primers can bind- preventing loss of DNA
Hayflicks constant
maximum number of times a cell can divide without telomerase = 61.3 in human cells
mitosis order
prophase prometaphase metaphase anaphase telophase cytokinesis
mitosis: prophase
- Nuclear envelop disintegrates
- Chromosomes condense
- Mitotic spindle starts to forms
mitosis: prometaphase
spindles form from centrioles and connect with kinetochore of chromosomes
mitosis: metaphase
chromosomes randomly line up at the metaphase plate
mitosis: anaphase
- Kinetochore microtubules pull chromatids towards the poles
- Go to different poles (now become chromosomes (not called chromatids anymore)
mitosis: telophase
- Spindle disappears
- Nuclear membrane reforms
- Nucleolus reappears
- Chromosomes decondense
mitosis: cytokinesis
cleavage of daughter cells with equal number of chromosomes
mitosis overview
cell division for somatic cells
–> Production of two identical daughter cells
o Same number of chromosomes content as parental cell
- Important during development (~50 mitotic rounds) and mitotic growth (epidermis, mucosae, bone marrow, spermatogenesis)
in humans the haploid cells created by meiosis are
sperms and eggs
meiosis is
division for germ line cells
- Oogenesis
- Spermatogenesis
meiosis produces
4 non-identical cells - half chromosome content of parental cell (2n–> n)
how many rounds of replication and division in meiosis
- one round of replication
- two rounds of division- to separate sister chromatids
outline meiosis I
1) Prophase I: 1) Chromosomes begins to condense and pair up (homologous chromosomes (from mums and dad) will look for each other)
2) Metaphase I: spindle begins to capture chromosomes and move them towards the centre of the cell- metaphase plate
- Each chromosome attaches to microtubule from just one pole of the spindle
- Homologous pairs not individual chromosomes line up for separation.
3) Anaphase I: homologues are pulled apart and move apart to opposite neds of the cell
- Sister chromatids of each chromosome remain attached to one another and
don’t come apart
4) Telophase I: chromosomes arrive at opposite poles of the cell
- Cytokinesis occurs at the same time as telophase I
- Cleavage- formation of two haploid non-identical daughter cells
when does homologous recombination occur and how
during Prophase I via crossing over
explain crossing over
o DNA is broken at the same spot on each homologue and exchange part of their DNA
o Crossing over occurs as chiasmata- cross shaped structures where homologues are linked together
o Chiasmata keep homologues connected
o Can have multiple cross overs
meiosis II
Cells move from meiosis I to II without copying their DNA. Meiosis II is a shorter and simpler process than meiosis I basically ‘mitosis for haploid cells’.
- Cells that enter meiosis II are made in meiosis I
- Cells are haploid and have one chromosome from each homologues pair
- But chromosomes still consists of two sister chromatics
- In MII sister chromatids separate, making haploid cells with nonduplicated chromosomes
outlines meiosis II
1) Prophase II: Chromosome condense and nuclear envelop breaks down- if needed
- Centrosomes move apart
- Spindle forms between them
- Spindle microtubules begin to capture chromosomes
- Two sister chromatids are captures by microtubules from opposite spindle poles
2) Metaphase II: the chromosomes line up individually along the metaphase plate.
3) Anaphase II: sister chromatids separates and are pulled towards opposite poles of the cell
4) Telophase II: nuclear envelopes form around each set of chromosomes and the chromosomes decondense.
- Cytokinesis splits the chromosome set into new cells
- Forming 4 haploid cells in which each chromosomes has just
describe oogenesis
1) Primary oocyte (2n) divides to form 1 secondary oocyte (1) and 1 polar body
2) The secondary oocyte (n) divides to form ovum (n)
polar bodies in oogenesis
4 polar bodies in total produced (2 from original polar body and one from secondary oocyte
describe spermatogenesis
1) Primary spermatocyte (2n) divides to form 2 secondary spermatocyte (n)
2) Secondary spermatocytes divide to form 4 spermatids
3) 4 spermatids mature into sperm
importance of meiosis
introduces variation
meiosis introduces variation via
- random segregation
- independent assortment
- crossing over
non-disjunction
results in variations in chromosome number, which can occur in both meiosis I and II
- e.g. aneuploidy
which meiosis is non-disjunction most harmful in
meiosis I
- non of the cells face a correct number of chromsomes
sources of DNA damage
endogenous
exogenous
endogenous sources
- replication stress
- reactive oxygen species
- intrinsic instability of DNA (hydrolysis, oxidation, methylation)
exogenous DNA damage
- chemical radical
- ionising irradiation
- UV light
name some types fo DNA damage
ss break mismatch damaged base ds break intrastrand cross link interstrand crossline
DNA damage response (3)
- senesence
- proliferation
- apoptosis
replication stress defined as
‘Inefficient replication that leads to replication fork slowing, stalling and/ breakage.’
Replication stress can be caused by:
1) Replication machinery defects
2) Replication fork hindrance
• Forward and backward slippage
• e.g. Trinucleotide repeats
3) Defects in response pathway
1) Replication machinery defects
- Misincorporation by DNA polymerase
* Proofreading error by DNA polymerase
2) Replication fork hindrance
Repetitive DNA can lead to fork slippage
Forward slippage (deletion mutation)
• New strand has an extra nucleotide (A)
• Newly synthesised strand loops out
Backward slippage (insertion mutation)
• New strand is missing a nucleotide (A)
• Template strand loops out
example of a disease caused by replication fork progression hindrance
Fork slippage leads to trinucleotide expansion
e.g. Huntington’s (backward slippage)
- HTT gene
- Trinucleotide CAG repeats- polyglutamine repeats
increased CAG repeats in Huntington’s causes
neurone degeneration
replication machinery defects
DNA polymerase has a 3’ to 5’ DNA exonuclease domain and proofreads leading to the right nucleotide in its place. However, sometimes mismatches occur. Other enzymes involved in the replication can also be faulty such as topoisomerase or helicase.
defects in response pathway
repair doesn’t occur at the checkpoints
DNA repair techniques
1) Base excision repair
2) Nucleotide excision repair
Double strand break repair mechanisms (high energy radiation)
- non-homologous end joining
- homologous recombination (better)
what can proteins act as
RITE
R
receptors
I
ion channels
T
transporters
E
enzymes
structural unit of proteins
amino acids
what joins amino acids
peptide bonds
properties of peptide bond
planar
rigid
stereosiosmerism
amino acids are classified according to their
R groups properties
pKa is a
pKa value is one method used to indicate the strength of an acid. pKa is the negative log of the acid dissociation constant or Ka value. A lower pKa value indicates a stronger acid. That is, the lower value indicates the acid more fully dissociates in water.
if there is a negatively charged froup
loss of hydrogen has occured
if an R group can donate hydrogen
it is acidic
lower pKa
more acidic
if pH
R group is protonated
if pH> pKa
R group is deprontonated
pKa equation
pKa = -log (Ka)
pI
isoelectric point
isoelectric point
pH at which there is no overall net charge
if pH
protein protonated
if pH>pI
protein is deprotonated
protein folding
- primary
- secondary
- tertiary
- quaternary
primary structure
linear amino acid sequence
secondary structure
local spatial arrangement of polypeptide backbone to for an alpha helix or beta pleated sheet
tertiary structure
3D configuration with further folding
quaternary structure
different polypeptides join, sometimes with a prosthetic group
bonds in primary structure
Covalent
- peptide
- disulphide (between cysteine)
bonds in secondary structure
- hyrogen
- peptide
- disulphide
bonds in tertiary structure
- hydrophobic bonds
- hydrogen bonds
- ionic bonds
- van der waal forces
- disulphide
bonds in quaternary structure
- hydrophobic
- hydrogen
- ionic
- van der waals
- disulphide
fibrous proteins
Long and anrrow- role in providing structural support
fibrous protein solubility
mostly insoluble
sequence of amino acids in fibrous proteins
repetitive
stability of fibrous proteins
less sensitive to changes in heat and pH
examples of fibrous proteins
collagen and keratin
globular proteins
rounded/spherical- role is functional (catalysts and transport)
solubility of globular proteins
soluble
sequence of amino acids in globular proteins
irregular
stability of globular proteins
more sensitive to changes in heat and pH
examples of globular proteins
hb, insulin and catalse
enzyme models
- lock and key
- induced fit
enzymes
lower the activation energy required for a reaction to occur
which equations can be used to predict the Vmax and Km of an enzyme
Michaelis- menten and Lineweaver Burk Plot
how to recognise Michaelis menton
hyperbole shape
- Velocity vs [substrate]
how to recognise Lineweaver Burk plot
straight lines
Vmax
rate of reaction when the enzyme is fully saturated by substrate, indicating that all the binding sites are constantly reoccupied
Km is the
substrate concentration that give gives half Vmax
the lower the Km
the higher the affinity for the substrate
types of enzyme inhibition
competitive
non-competitive
competitive
inhibitor binds to active site - directly blocking the active site for the substrate
non-competitive
changes the shape of the active site by bnidnign to allosteric site
inhibitors are molecules which
slow down of prevent enzyme reaction. they can be irreversible or reversible
reversible competitive inhibitors
adding more substrate can override the effect on the enzyme
- as a result the Vmax is unaffacted but the Km will increase
reversible non-competitive inhibitor
the Vmax decreases but Km is unaffected
what can cause irreversible damage to enzymes
denaturation, pH and temp
energy is the capacity to
do work and exists in may forms
food has stored
chemical enegry
humans require energy for
- biosynthesis work
- transport work
- mechanical worj
- electrical work
what is the official SI unit of food enegry
Kj
what do doctors usually use to explain energy in food
calories
1kcal is equal to how many KJ
4.2KJ
catabolism
catabolism breaks large molecules into smaller ones
anabolism
anabolism builds complex molecules from simpler ones
what are essential components of the diet
- carbohydrates
- proteins
- fats
- mineral
- vitamins
- fibre
examples of carbohydrates
starch, sucrose, fructose, glucose, maltose, glycogen
monosaccharides
glucose
fructose
galactose
disaccharides
maltose
lactose
sucrose
maltose
glucose-glucose
lactose
galactose-glucose
sucrose
glucose-fructose
list the 9 essential amino acids (pneumonic)
If Learned This Helpful List May Prove Truly Valuable
Isoleucine Leucine Threonine Histidine Lysine Methionine Phenylalanine Tryptophan Valine
why may children and pregnant women require amino acids added to their diet
high rate of protein synthesis
e.g. need extra arginine, tyrosine and cysteine
fat contains less
oxygen compared to hydrogen than carbohydrates or proteins
fat has less oxygen and this means
it becomes more reduced and yields more oxygen when oxidised
fats provide a source of
essential fatty acids ( linoleum and linolenic) which can’t be synthesised in the body
minearls
required to maintain ion gradients, calcium and phosphorus for structure, signalling, enzyme cofactors (iron, magnesium, copper, zinc, manganese) and haemoglobin
vitamins
e.g. A, D, K, C, folate, B6
essential for life and can lead to deficiency diseases
Vitamin A deficiency
xerophthalmia
Vitamin D deficiency
rickets
Vitamin K deficiency
defective blood clotting
Vitamin C deficiency
scurvy
folate deficiency
neural tube defects and anaemia
B6 deficiency
dermatitis
BMI calculation
weight (kg)/ height (m^2)
obesity is due to
excessive energy intake which is stored in adipose tissue
when does obesity occur
when energy intake> energy expenditure
what can obesity cause?
T2D
CHD
Osteoarthritis
Cancers
underweight BMI
<18.5
normal BMI
18.5- 24.9
overweight BM
> 25
obese BMI
> 30
severely obese BMI
> 40
main two conditions which occur in malnutrioned children
- Marasmus
- Kwashiorkor
Marasumus characterised by
not having too low protein (non oedema)
outline marasmus
- calorific deficiency and protein deficiency
- children under the age of 5
- muscle wasting
- emaciated
- loss of body fat
- thin hair
- diarrhoea
- anaemia
outline kwashiorkor
- protein deficiency
- children displaced from breastfeeding
- ascites and oedema (starling forces`)
- hepatomegaly (fat deposition- causes abdominal distension)
- thin limbs
