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51 Cards in this Set
- Front
- Back
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How many base pairs are there per turn in B-DNA and what shape is it? |
10.5 base pairs per turn Right handed double helix with 2 antiparallel strands forming major and minor grooves |
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Why is DNA negative? |
Sugar phosphate backbone |
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What stabilises DNA? (2) |
- Hydrogen bonds - Hydrophobic base stacking |
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What is the difference between a nucleotide and a nucleoside? |
Nucleotide = base + sugar + atleast one phosphate Nucleoside = base + sugar |
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GIve 2 examples of purine bases. |
Adenine and Guanine |
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Give 3 examples of pyrimidine bases |
Cytosine, Thymine and Uracil |
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What do phosphodiester bonds link in DNA and RNA? |
3' carbon of one pentose sugar to 5' carbon of neighbouring pentose |
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What do you find at the free 5' and 3' ends of a nucleic acid? |
5' = phosphate 3' = OH |
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What makes RNA less stable than DNA? |
The OH on the 2' carbon makes the adjacent phosphodiester bond susceptible to alkaline hydrolysis |
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Compare DNA and RNA (5) |
DNA - Up to 10^10 ntds - 2' deoxyribose - alkali stable RNA - Up to 10^7 ntds - Ribose - alkali labile |
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Give 2 examples of secondary structure in nucleic acids. |
Organisation into double helix (DNA) and stem loops (both) |
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Give an example of tertiary structure in nucleic acids. |
Supercoiling (DNA) |
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Give 3 examples of quaternary structure in nucleic acids. |
Ribosomes, spliceosomes, mRNPs (all RNA) |
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Describe viral genomes. (4) |
- Can be DNA/RNA - Can be single or double stranded - Contain few genes - Rely on host genes |
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Where can circular DNA be found (2) |
- Bacteria - Mitochondria |
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How can RNA act like an enzyme? |
Precursor RNAs can catalyse the splicing of themselves to remove UTRs |
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Give the - structure - number of bases per turn - regions that favour Z DNA. |
- Left handed double helix with zig zag backbone - 12 bp - GC rich regions with lots of 5-methyl-C |
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What is a cruciform and where does it form? |
Intrastrand base pairing forms fold Forms where inverted repeat sequences present |
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What cause the dentauration temperature of DNA to increase? |
Increased GC content |
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Define the melting temperature (tm) of DNA. |
the temperature at which half theincrease in absorbance at 260 nm occurs |
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What is a microarray and what is it used for? |
Glass slide with probes for thousands of genes that cDNA can hybridise to Finding out gene expression in different tissues |
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What can assess secondary structure of RNA? |
X-ray crystallography |
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What can modify secondary structure in RNAs? |
Interactions with proteins |
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How many stem loops are there in a tRNA and what is their role? |
Three - enzyme recognition - one has anticodon for binding to mRNA |
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Where do amino acids bind to tRNAs? |
3' end |
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What is 16S ribosomal RNA? |
Large RNA molecules with lots of stem-loops which interact in specific ways with ribosomal proteins |
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How many subunits are there in a ribosome and what do they consist of? |
Two RNA molcules and small, basic proteins |
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Give 3 features of supercoiling. |
- Introduced by enzymes using ATP - Occurs where runs of AT base pairs occur at regular intervals - Right handed in nature |
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How many types of histone protein are in each nucleosome? |
5 (two of each protein in bead, one (H1) not in bead and only one copy) |
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How are histone genes unusual? |
Very highly conserved and multiple copies of each as so much histone required |
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What is euchromatin? |
OpenDNA with nucleosomes spaced along it that is genetically active |
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What is the 30nm fibre? |
Solenoid of nucleosomes stabilised by H1 histone interactions |
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What is heterochromatin? |
Wound up DNA that is genetically inactive |
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Give 3 examples of non-histone chromosomal proteins. |
DNA and RNA polymerases Gene regulatory proteins |
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What primes DNA synthesis and what enzyme is involved? |
RNA Primase |
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What prevents DNA polymerase binding rNTPs? |
Discriminator amino acids in DNA pol |
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Which direction does DNA have to be synthesised in? |
5' to 3' |
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How is DNA replication finished off? (3) |
- RNA fragments removed by RNAase - DNA pol. fills in gaps - DNA ligase seals strands |
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What is the role of topoisomerase? |
Relaxes DNA so can be accessed by enzymes |
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What keeps strands apart in DNA replication? |
single stranded DNA binding protein |
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Compare prokaryotic and eukaryotic DNA replication. |
Prokaryotes - DNApolymerases III and I - RNA primers and Okazaki fragmentsshorter - One origin Eukaryotes - DNA polymerases delta and alpha - RNA primers and Okazaki fragments longer - Multiple origins |
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How is DNA replication initiated in bacteria? What controls the timing? |
Initiator protein (DnaA hexamer) bound to oriC start site DNA methylation of oriC |
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What intiates DNA replication in eukaryotes? |
Origin recognition complex binds to origin and attract other proteins |
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What is the 'end' problem in eukaryotes? What is the solution? |
Chromosome would shorten each time due to unrepaired Okazaki fragments at 5' end Telomeres (TG rich sequence) where 3' end sticks out and is extended by telomerase so 5' end can be extended by RNA primer and DNA pol |
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What is the structure of telomerase? How does it extend the 3' end of DNA? |
Enzyme containing a short RNA molecule complementary to the TTAGGG repeats which acts as a template for reverse transcription |
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How are telomeres related to aging? |
Get shorter as you grow older as telomeraseactivity in somatic cells decreases |
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Name 3 DNA repair mechanisms. |
- Double strand break repair - Base excision repair - Nucleotide excision repair |
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Name 5 causes of DNA breaks. |
- Radiation - Chemicals - Radicals - V(D)J recombination - meiosis |
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Why do we use thymine instead of uracil in DNA? |
Deamination of C to U is common therefore if use T all U present must be damaged |
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How are lesions that distort the double helix replaced (e.g. thymine dimers)? |
Nucleotide excision repair (substantial length of one strand removed and replaced) |
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What effect do DNA lesions have on replication? How is this solved? |
Block DNA pol. Bypass DNA pol. makes DNA opposite the lesion and allows the standard DNA pol to rebind and continue replicating |
