Cell biology - theme 3

Question 1

why might entry to interphase be delayed

Answer 1

delayed by entry into G₀ due to lack of mitogens to produce cyclin

Question 2

what does cyclin do

Answer 2

activate cyclin dependent kinases (CDKs) to drive cell through cell cycle by phosphorylation

Question 3

what do CDKs do

Answer 3

drive cell through cell cycle by phosphorylation
different CDKs for different phases of cell cycle
- S phase, increase S cyclin, increase CDKs for DNA replication
- M phase, increase M cyclin, increase mCDK activity

Question 4

what can cause cancer

Answer 4

mutated p53 protein allows damaged DNA to be in daughter cells of mitosis so they are mutated

Question 5

what does p53 protein do

Answer 5

DNA damage activates p53 to inhibit CDKs to block cell cycle at G1 to allow DNA repair

excessive DNA damage activates p53 to stimulate Bax to trigger apoptosis

Question 6

apoptosis

Answer 6

programmed cell death caused by cascade of intracellular caspases

Question 7

how is apoptosis suppressed

Answer 7

suppressed by mitogens and growth factors

Question 8

general steps for apoptosis

Answer 8

Fas ligand binds to cell with Fas receptor
cascade of intracellular caspases
cleaves cytoskeleton so detaches from adjacent cell
cell shrinks
DNAses fragment DNA
membrane changes to trigger phagocytosis
cell engulfed and digested by macrophages

Question 9

how does mitochondrial injury lead to apoptosis

Answer 9

damaged mitochondria leak cytochrome-c

cytochrome-c activates caspases

Question 10

necrosis

Answer 10

accidental cell death caused by acute physical and chemical injury

Question 11

steps of necrosis

Answer 11

cell swells and bursts (lysis)
releases contents
triggers inflammatory response
damage

Question 12

non-disjunction

what does it cause

Answer 12

homologous chromosomes do not separate so one cell has none and other has two
aneuploidy and polyploidy

Question 13

aneuploidy

Answer 13

loss or gain of one or more chromosomes

Question 14

trisomy

e.g. Down’s, Edward’s

Answer 14

type of aneuploidy where 1 chromosome is gained
Down’s 21
Edward’s 18

Question 15

monosomy

e.g. Turner’s

Answer 15

type of aneuploidy where 1 chromosome is lost

Turner’s lack of X or Y

Question 16

polyploidy

Answer 16

addition of one or more complete haploid chromosomes

Question 17

triploidy

Answer 17

type of polyploidy where 3 of each chromsome so 69 chromosomes

Question 18

translocation

Answer 18

a piece of chromosome form one homologous part breaks off and join chromosome from a different pair

Question 19

what prevents G1 -> S phase

Answer 19

p27 protein inhibits CDKs

Question 20

germline mutations

Answer 20

occur in germ cells/ gametes

inherited disease

Question 21

somatic mutations

Answer 21

occur in somatic/ adult cells during development or adult life
not inherited

Question 22

dominant-negative mutation

Answer 22

loss of function due to interference of mutant gene product with normal gene product of corresponding allele

Question 23

types of nucleotide deletion mutations (3)

Answer 23

multiple of 3 (codon) - in frame deletion removes one amino acid

not multiple of 3 - frameshift loses protein expression and function

larger deletions - partial/ whole gene deletion, complete loss of protein expression and function

Question 24

types of nucleotide substitution mutations

by replacement of nucleotide (2)

Answer 24

transition - substitution of same base type e.g. purine for purine

transversion - substitution of different base type e.g. purine for pyrimidine

Question 25

types of nucleotide substitution mutations

effect of gene/ protein expression/ function (5)

Answer 25

silent - codes for same amino acid, no effect

missense - encodes different amino acid

nonsense - introduces stop codon

splice site - aberrant splicing results in exon skipping or intron retention

promoter or regulatory element - altered expression levels

Question 26

errors in DNA repair (4)

Answer 26

mismatch repair - corrects mismatched bases in DNA replication

nucleotide excision repair - removes thymine dimers and DNA adducts

base excision repair - removes abnormal bases

post replication repair - removal of double stranded breaks by homologous recombination

Question 27

chemical damage to DNA e.g.

Answer 27

alcohol, toobacco form DNA adducts cause depurination (deletion) or deamination (substitution)

Question 28

physical damage to DNA e.g.

Answer 28

ionising radiation e.g. X rays causes double strand breaks

UV light form thymine dimers

Question 29

causes of DNA mutation

Answer 29

DNA replication errors by proofreading mistakes of DNA polymerase
chemical damage
physical damage
errors in DNA repair

Question 30

mutation of sickle cell anaemia

Answer 30

beta globin mutation A-T transversion

GAG -> GTG so Glu to Val

Question 31

mutation

Answer 31

DNA variant with frequency <1% population

Question 32

polymorphism

Answer 32

DNA variant with frequency >1% population and must have two alleles

e.g. single nucleotide polymorphism (SNP)

Question 33

polygenic traits

Answer 33

influenced by other genes

Question 34

multifactorial traits

Answer 34

influenced by interaction of genetic and environmental factors