7 NUCLEIC ACIDS Flashcards
Non-coding (for proteins) DNA
Satellite DNA - short tandem repeats used in DNA profiling
Telomeres - at the end of chromosomes prevent their deterioration
Introns - removed before splicing
Non-coding tRNA genes - code for t-RNA
Gene regulatory sequence - promoters, silencers
Hershey and Chase
- viruses (bacteriophage) grown in an isotopic medium
- P32 proteins radiolabelled
- S35 DNA radiolabelled
- infect E.coli bacteria
- centrifuged in a blender to form a pellet (bacteria) and supernatant (viruses)
- pellet was radioactive when infected with P32
Conclusion: it was known that genetic material was transferred from viruses to bacteria and it was found that DNA holds the genetic material
-
Rosalind Franklin’s X-ray diffraction
- double stranded
- helix
- phospates out, N in
Outline the process of DNA replication.
- helicase unwinds
- gyrase reduces strain
- DNA primase attaches RNA primer
- DNA polymerase III attaches nucleotidea from 5’ to 3’ direction
- DNA polymerase I detaches primers and attaches nucleotides
PCR
- polymerase chain reaction
-1. Denaturation - separate to two strands
2. Annealing - attachement of a primer
3. Elongation - Taq polymerase attaches nucleotides
Dideoxyribonucleotides stop DNA replication
- DNA replication using PCR
- set like PCR for each of the four tubes
- in each a specific dideoxynucleotides is added
- different lengths of DNA produced becasues when dideoxynucleotides Bind to a complimentary base the replication is stopped
- gel electrophoresis used
- read from the bottom, and the sequence is the complimentary one
What modifications are done to mRNA after transcription?
Capping 5’
Splicing
Polyadenylation 3’
Quaternary structure
Between many polypeptide chains
Or
Prosthetic group i.e. heme group —} conjugated system
Gene expression regulated by proteins that Bind to specific DNA regions
- Transcription factors bind to promoters and mediate binding of RNA polymerase
- regulatory proteins bind to enhancers and silencers
Explain transcription [7]
a. synthesis of RNA/mRNA / transcription of DNA to RNA;
b. RNA nucleotides linked together to form a strand/chain;
c. RNA strand assembled on DNA template/antisense strand / copy made of sense strand;
d. RNA polymerase carries out transcription/links RNA nucleotides;
e. uncoiling/separation of DNA strands;
f. 5’ end of nucleotides linked to 3’ end of (growing RNA) strand;
g. complementary base pairing (is the basis of copying the base sequence);
h. uracil instead of thymine in RNA;
i. starts at/RNA polymerase binds to a promoter;
j. regulated by transcription factors/DNA binding proteins/nucleosomes;
Explain the control of gene expression in eukaryotes.
a. mRNA conveys genetic information from DNA to the ribosomes «where it guides polypeptide production»
b. gene expression requires the production of specific mRNA «through transcription»
c. most genes are turned off/not being transcribed at any one time/regulated
OR
some genes are only expressed at certain times
d. some genes are only expressed in certain cells/tissues
OR
«cell» differentiation involves changes in gene expression
e. transcription factors/proteins can increase/decrease transcription
f. hormones/chemical environment of cell can affect gene expression
g. example of cell environment
eg: auxin/insulin/cytoplasmic gradient in embryo
h. transcription factors/proteins may prevent or enhance the binding of RNA polymerase
i. nucleosomes limit access of transcription factors to DNA/regulate gene expression/transcription
OR
activate or silence genes
j. DNA methylation/acetylation appears to control gene expression «as epigenetic factor»
OR
methylated genes are silenced
k. «some» DNA methylation patterns are inherited
l. introns may contain positive or negative gene regulators
OR
gene expression can be regulated by post-transcriptional modification/splicing/mRNA processing
Outline the roles of the different binding sites for tRNA on ribosomes during translation.
A, P and E binding sites are on the large subunit of the ribosome
b. initiation of translation starts with binding of met-tRNA to the start codon
c. large sub-unit binds with «start» tRNA in the P site
d. A binding site holds the tRNA with the next amino acid to be added
e. peptide bond is formed between the amino acids of the A site and the polypeptide at the P site
f. polypeptide is transferred to the tRNA in the A site
g. the tRNA «with polypeptide» in A site then moves to P site
OR
P binding site holds the tRNA attached to the growing polypeptide
h. E binding site «exit» is where the tRNA «from P site without amino acid» leaves the ribosome
Explain DNA replication.
helicase unwinds the double helix
b. gyrase/topoisomerase relieves strains during uncoiling
c. helicase separates the two strands of DNA/breaks hydrogen bonds
Accept unzips here but not for mark point a.
d. each single strand acts as a template for a new strand / process is semi-conservative
e. DNA polymerase III can only add nucleotides to the end of an existing chain/to a primer
f. (DNA) primase adds RNA primer/short length of RNA nucleotides
g. DNA polymerase (III) adds nucleotides in a 5’ to 3’ direction
h. complementary base pairing / adenine to thymine and cytosine to guanine
Do not accept letters.
i. DNA polymerase (III) moves towards the replication fork on one strand and away from it on the other strand
j. continuous on the leading strand and discontinuous/fragments formed on the lagging strand
k. DNA polymerase I replaces primers/RNA with DNA
l. ligase joins the fragments together/seals the nicks
Explain how polypeptides are produced by the process of translation. [8]
mRNA is translated;
b. mRNA binds with ribosome/with small subunit of ribosome;
c. tRNA-activating enzymes/aminoacyl tRNA synthetases attach specific amino acid to tRNA;
d. anticodon of 3 bases/nucleotides on tRNA;
e. start codon/AUG on mRNA;
f. tRNA carrying first amino acid/methionine binds to P/peptidyl site (when large subunit binds);
g. anticodon (on tRNA) binds to codon (on mRNA);
h. complementary base pairing (between codon and anticodon);
i. tRNA for next codon binds to A site/amino acyl site;
j. peptide bond forms between amino acids (on tRNAs) at P and A sites;
k. ribosome moves along mRNA to next codon/by three bases/in 5’ to 3’ direction;
l. tRNA released from E/exit site;
m. process/cycle repeats to elongate the polypeptide/until stop codon is reached;
n. release of polypeptide and mRNA/disassembly of ribosome complex at stop codon;
