Lecture 4: DNA and Chromosomes Flashcards
what are the stages of DNA replication
interphase - G1 (cell growth) - S (DNA replication) - G2 (DNA checking) mitosis - prophase - prometaphase - metaphase - anaphase - telophase cytokinesis
what are telomeres for
protect end of chromosome from fraying
what do the spindle fibres attach to
kinetochore which forms around the centromere
what happens during prophase
- chromosomes condense
- mitotic spindles form
- intact nuclear envelope
what happens during prometaphase
- nuclear membrane disintegrates
- spindle microtubules attach to kinetochores
what happens during metaphase
chromosomes align at equator
what happens during anaphase
sister chromatids separate and are pulled towards opposite spindle poles
what happens during telophase
- chromosomes arrive at poles
- nuclear envelopes reform
- contractile ring starts to form in the middle
what happens during cytokinesis
- nuclear envelopes completed
- contractile ring creates cleavage furrow
- cytoplasm divides, creating two daughter cells
what is the rate of mitosis controlled by
the phosphorylation of cyclin-dependent kinases (CDKs)
which regulator checks for damaged DNA in the G1 phase
p53, muttion in this causes 50% of cancers
in which direction is DNA synthesised during replication
5’ to 3’
what are the effects of DNA being replicated in multiple locations
- a leading strand with continuous synthesis
- lagging strand is read in the opposite direction, so has discontinuous synthesis
- lagging strand forms Okazaki fragments
outline the steps of DNA replication
- DNA primase adds RNA primer onto lagging strand, allowing DNA polymerase to bind
- binding proteins hold single stranded DNA straight
- ligase joins together small gaps
- nuclease cuts DNA, and exonuclease removes RNA primer
what is Werner’s Syndrome
- caused by mutation in DNA helicase, which causes errors in DNA replication and repair
- premature aging disorder
- increases risk of cataracts, atherosclerosis, osteoporosis and cancer
what is Xeroderma Pigmentosum
- mutation to UV repair system
- UV light causes formation of thymine dimers, and XP sufferers can’t remove these
- causes acute sun sensitivity
- hypo and hyper pigmentation
- multiple cancers at young age
- intellectual disability
- progressive degeneration
which mechanismss prevent accumulation of mutations
- DNA checking done by DNA polymerase during replication
- excission repair systems throughout cell life repair DNA damage
what are single nucleotide polymorphisms
- single base change in DNA sequence
- results in normal genetic variation of population
- synonymous causes no change in amino acid sequece
- non-synonymous causes a change in amino acid sequence
what is sickle cell anaemia caused by
single base substitution in HBB gene on chromosome 11
is sickle cell anaemia a loss or gain of function
loss
what does sickle cell anaemia cause
- haemoglobin beta chain gets sticky ad forms rigid rods
- red cells become a sickle shape
- clogs up capillaries and red blood cells get stuck
- patients susceptible to strokes and heart attacks
what is cystic fibrosis caused by
deletion of 8 base pairs in CTFR gene
is cystic fibrosis a loss or gain of function
loss
what does cystic fibrosis cause
- misfolding of protein involved in chloride transport, so it can’t be transported to the cell surface
- loss of chloride transport leads to mucus build up on lungs
what is Huntington’s disease caused by
insertion of CAG trinucleotide repeats in HTT gene
- normal range is 6-35
- can be a carrier between 36-29
- sufferers have 40-120
is Huntington’s a loss or gain of function
gain
what does Huntington’s disease cause
- CAG repeats code for glutamine, and polyglutamines stick together which is toxic and causes neuronal cell death
- causes uncontrollable muscle movements
- loss of memory and depression
- difficulties in speech and swallowing
