What is the diameter of packed chromatin fibres?
30nm
Which protein carries others into the nuclear envelope?
Importin
What initiates transcription in prokaryotes?
Sigma factor binding to Pribnow box and then RNA polymerase to bind, mRNA detachment from DNA occurs due to a repeated mRNA sequence of V
When are inclusion bodies created?
When enzymes cannot be targeted to lysosomes
What is initiator tRNA in prokaryotes and eukaryotes respectively?
fmet-tRNA and met-tRNA
How many triplet codons are there?
64
How many rings does a purine have?
2
How is the destination of a protein determined?
By the signal sequence of the protein
What causes aneuploidies?
Nondisjunction during oogenesis
What is the diameter of an entire mitotic chromosome?
1.4 um
Which amino acids are polar?
Arginine, asparagine, aspartate, glutamate, glutamine, lysine, serine, thereonine, tyrosine, histadine
Where is the restriction point?
Between M and G1
What is Ras?
The gene that regulates actin and microtubules skeletons causing transformation of cell type
How many chromosomes are in a normal human karyotype?
46
What is the point mutation leading to sickle cell anaemia?
GAG = GTG so glutamate becomes valine
How will a protein destined for the interior of the endoplasmic reticulum get there?
Binds to signal recognition particle (SRP) which binds to receptor on ER membrane
When does the nuceolous disappear
Prophase
What is a metacentric chromosome?
Has the centromere in the middle
What catalyses entry into S phase?
Cdk1
What are LINES and SINES?
Retrotransposable elements (moderately repetitive) Viral are LINES (long interspersed elements) Non viral are SINES (short interspersed elements)
Which enzyme repairs DNA in eukaryotes?
DNA polymerase beta and epsilon
How may gene mutations will lead to cancer?
5-7
How long does G1 last?
6-9 hours
How many genes are in the human genome?
23,000
Describe thymine.
A pyrimidine and methyl group
What is the pKa of histadine?
6
What is genetic anticipation?
Where a disease becomes more severe or appears earlier in successive generations
When do chromosomes line up on the spindle?
Metaphase
How many nucleotides per turn are there in DNA?
10
How much of the genome encodes proteins?
1.5%
When does the spindle begin to form?
Prophase
When do the chromosomes decondense?
Telophase
Where do vesicle and target cell bind to fuse?
At v-SNARE (vesicle) and t-SNARE (target)
What joins DNA polymerise III to the section of DNA it’s working on?
The sliding clamp
What does the antibiotic streptomycin do?
Affects initiation at the 30S subunit and causes the misreading of codons
When does the nuclear envelope reform?
Telophase
Which cyclin controls G2-M phase?
Cyclin B
What does the antibiotic erythromycin do?
Binds to 50S subunit and prevents translocation
Which enzyme forms replication forks in DNA replication?
DNA helicase
What does the nucleotase enzyme do?
Removes wrong nucleotides so the correct gene is copied without mutation
How do stop codons stop prokaryotic transcription?
Forming a hair pin loop due to GC rich region
How long does S phase last?
8-9 hours
What is the start codon?
AUG
What is a satellite on a chromosome?
The short part connected to the centromere by a stalk
What is an aneuploidy?
Abnormal number of chromosomes in a cell
What does cycloheximide do?
Inhibitor of protein biosynthesis in eukaryotic organisms by interfering with translocation step
What are proteins destined for lysosomes tagged with?
Mannose-6-phosphate
What is hnRNA?
mRNA which is yet to undergo splicing
Name 5 X-linked disorders.
Red-green colour blindness, Haemophilia A, Haemophilia B (xmas disease), Duchenne muscular dystrophy and Becker’s muscular dystrophy
What is the pKa of arginine?
12.5
Which cyclin controls S-G2 phase?
Cyclin A
What is the pKa of glutamate?
4.2
When do sister chromatids separate?
Anaphase
What does the antibiotic chloramphenicol do?
Inhibits pepdiyl transferase by binding to 50S subunit
What loads the amino acids onto tRNA?
Aminoacyl-tRNA-synthetases
How do chromosomes attach to the spindle in prometaphase?
Via kinetochores
What is positive supercoiling?
Separation of 2 strands by DNA helicase causes tighter coiling further down the helix
Why do malignant tumours grow more quickly than benign?
No tumour capsule so can invade organs and tissues
Which bonds join nucleotide monomers?
Phosphodiester bonds
What is polyadenylation?
Essentially 50-250 adenosine residues added to 3’ end of RNA chain in mRNA processing to form a tail
What is the prokaryotic 70S complex made of?
A large subunit (50S): 23S rRNA + 5S rRNA + 34 proteins
A small subunit (30S): 16S rRNA + 21 proteins
What does the antibiotic rifamycin do?
Inhibition of DNA dependant RNA synthesis through binding to prokaryotic RNA polymerase
How many chromosome pairs are in the human genome?
3 x 10^9
When does the cell enter G0?
If no signal is received from external mitotic agent during G1
Describe adenine.
A purine with an amino group and no carbonyl group
When do chromosomes condense?
Prophase
What an Okazaki fragments?
Discontinued sections of the replicated lagging DNA strands
Describe uracil.
A pyrimidine with neither amino or carbonyl groups.
How does reverse transcriptase create so many mutations in HIV virus replication?
Has no error checking ability
How long does M phase last?
1-2 hours
What is the mitosis promoting factor?
Cyclin dependant kinase
Which enzyme synthesises leading strand in eukaryotes?
DNA polymerase delta
What is an acrocentric chromosome?
Has a short arm consisting of only a satellite.
What is cyclin B doing for entry into mitosis?
Regulating
Which amino acids are acidic (negatively charged)?
Aspartate, glutamate,
What is the sequence at the 3’ end of tRNA?
CCA-OH
What do CO2 and BPG do to haemoglobin affinity for O2?
Decrease affinity
What causes termination of translation?
Binding of release factors 1 or 2 hydrolyses protein from tRNA. Requiring IF3 and ribosomal recycling factor and GTP hydrolysis
How does UV damage DNA?
Creates thymine dimers
What is an intron?
Regions of non coding DNA within genes
What is the chromosomal abnormality in Patau syndrome?
Trisomy 13
Which amino acids are essential?
Histadine, isoleucine, leucine, lysine, methionine, phenylalanine, thereonine, tryptophan
What is chromatin remodelling?
The dynamic modification of chromatin architecture to allow access of the condensed genomic DNA to the regulatory transcription making proteins- controlling gene expression
When does DNA synthesis occur?
In S phase only
What is the chromosomal abnormality in Down’s syndrome?
47 XX + 21 (females) or 47 XY + 21 (males)
What are indels?
Insertions or deletions of a small number of nucleotides
Which enzyme synthesises lagging strand and primers in eukaryotes?
DNA polymerise alpha
What does the antibiotic actinomycin do?
Binding DNA at transcription initiation complex and preventing elongation by RNA polymerase
What is the rate of aneuploidy conceptions in humans?
1 in 160
What does activated amino acid bind to in elongation of translation?
Elongation factor EF-Tu GTP
Which amino acids are basic (positively charged)?
Arginine, histadine, lysine
Which genes can inhibit the cell cycle between G1-S?
p53 and pRb
Which amino acids are non polar?
Alanine, cysteine, glycine, isoleucine, leucine, methionine, phenylalanine, proline, valine
What does deadly toxin alpha-aminitin do?
Inhibits RNA polymerase II
What does puromycin do?
Causes premature chain termination in translation and pro and eukaryotes
Which enzyme synthesises mitochondrial DNA in eukaryotes?
DNA gamma
Why would a recessive disease have a high carrier frequency?
There may be a selective advantage to being a carrier
Which way do polynucleotides read?
5’ to 3’
How is mRNA capped?
Joining 7-methylguanosine to the 5’ end by a 5’5’ triphosphate bridge
When does the spindle assembly checkpoint prevent anaphase?
When kinetochore is not attached to a chromosome
How does the T state of haemoglobin compare to the R state in terms of affinity for O2?
T state has a lower state of affinity than R
What does pre-mRNA contain?
Exons and introns. It’s capped and one end has a tail at the other
What is an X-linked disorder?
Carried on male chromosome and males are more likely to have it as females are usually carriers.
What will happen if cell cycle suppressors are phosphorylated?
The cell will enter the cell cycle
What is the long arm of a chromosome called?
The Q arm
Where does the amino acid attach to tRNA?
At the 3’ end
What is the pKa of aspartate?
3.9
What are tandem repeats?
A form of satellite DNA
Where does the S phase of the cell cycle happen?
Between G1 and G2
What does diphtheria toxin do?
RNA translational inhibitor by inactivating eukaryotic elongation factor 2
What does telomerase create?
Long sequences of short tandem repeats
Which amino acids are both ketogenic and glutogenic?
Isoleucine, phenylalanine and tyrosine
What does the Shine-Dalgario sequence in prokaryotes do?
Binds to rRNA to ensure in frame translation
What is the diameter of the DNA double helix?
2 nm
How does the cytoplasm divide?
Due to actin
What is a nucleosome?
DNA wound round histones
What is the miscarriage risk in amniocentesis?
1%
When does the nuclear envelope break down?
Prometaphase
Which cyclin controls G1-S phase?
Cyclin E
What is Klinefelter syndrome?
Boys born with an extra X chromosome causes a flabby body with low muscle tone, little facial and body hair, small testicles and penis, gynaecomastia
What is the diameter of condensed section of chromosome?
700 nm
Where is the anticodon on tRNA?
On the central loop
What does the antibiotic tetracycline do?
Inhibits binding of aminoacyl tRNA to the ribosome
When does the spindle disappear?
Telophase
What does initiation of transcription in prokaryotes require?
Initiation factors 1, 2 and 3 and GTP
How many hydrogen bonds are there in A-T base pairing?
2
How many hydrogen bonds are there in C-G base pairing?
3
What regulates entry into S phase?
Cyclin E
What does p53 do?
Tumour supressor gene, activated following DNA damage and induces transcription of p21 which inhibits the activation of cyclin-dependant kinase preventing entry into S or M phase
Which enzyme is responsible for joining DNA nucleotides in prokaryotes?
DNA polymerise III
Which end is the 5’ end and which is the 3’ end of a DNA strand?
5’ is phosphate group, 3’ is hydroxyl group
What is the short arm of a chromosome called?
The P arm
Describe cytosine.
A pyrimidine with an amino group
How long will a child with Edward’s syndrome (trisomy 18) usually survive?
Most do not live a year
How can a cell progress through the DNA damage cell cycle checkpoint?
Phosphorylation of tumour suppressor p53 and activation of p21 which deactivates cyclins
What is the Leucine zipper?
A 3D structural motif in proteins which is part of the DNA binding domain- regulates gene expression
What stabilises supercoiling forces?
Topoisomerase
Where are telomerases active?
In gametes
Which protein helps termination of prokaryotic transcription?
Rho
What is the main repressor of cell cycle transcription factors?
Rb
What is the ribosomal number and subunits in eukaryotic DNA?
80S with 40S and 60S subunits
What is wobble base pairing?
Pairing of mRNA bases to non complimentary tRNA bases
What is the diameter of unpacked chromatin fibres?
11nm
Describe guanine.
A purine with amino and carbonyl groups
Which enzyme joins Okazaki fragments?
DNA ligase
What is Cdk1 doing for entry into mitosis?
Catalysing
What repairs DNA and how?
06 methylguanine repairs DNA by removing DNA and resynthesising it
What are the stop codons?
UAA, UAG, UGA
What will deamination do?
Change base C to U
Which amino acids are ketogenic?
Leucine and lysine
When does cytokinesis begin?
Telophase
How do things enter the nucleus?
Via diffusion through nuclear pores for small things, via importins for large things
How are newly synthesised proteins tagged and moved to the ER?
The SRP binds to the signal sequence on the new peptide and the entire complex is pulled into the translocation channel of the ER
Which transcription factor controls entry into the cell cycle?
E2F
What kind of disease is Huntingdon’s disease?
Autosomal dominant
How many rings does a pyrimidine have?
6
How long does G2 last?
5-6 hours
Which amino acids contain sulphur?
Cysteine and methionine
