7 — nucleic acids Flashcards
1
Q
describe the function of three named enzymes involved in DNA replication (3)
A
- helicase unwinds DNA from double helix
- DNA gyrase releases tension caused by supercoiling
- DNA primase adds RNA primer
- DNA polymerase I removes RNA primer with DNA
- DNA polymerase III synthesises DNA on leading/ lagging strands
- DNA ligase connects okazaki fragments to make continuous DNA strand
2
Q
draw a labelled diagram to show the structure of a single nucleotide of RNA (3)
A
- ribose drawn as a pentagon and labelled
- base linked correctly to C1
- phosphate linked correctly to C5
3
Q
describe how DNA profiling can be used to establish paternity (5)
A
- DNA sample is collected from the child and its potential parents
- from saliva/ blood/ other body cells
- PCR used to amplify DNA
- short tandem repeats
- number of repeats varies between individuals
- unlikely that two individuals have same number of repeats for every gene included
- gel electrophoresis used to separate DNA fragments according to length and number of repeats
- gel electrophoresis generates a unique pattern of bands
- DNA profile is the pattern of bands
- all bands in the child’s profile must be in one of the parents’ profiles
4
Q
explain transcription (7)
A
- synthesis of RNA
- RNA nucleotides linked together to form a strand
- RNA strand assembled on DNA template
- RNA polymerase carries out transcription
- uncoiling of DNA strands
- 3’ end of nucleotides linked to 5’ end of growing RNA strand
- complementary base pairing
- uracil instead of thymine in RNA
- RNA polymerase binds to a promoter
- regulated by transcription factors
5
Q
explain how differentiation of cells and regulation of gene expression allow proteins such as insulin to be produced in only certain types of body cell (7)
A
- insulin production is determined by a gene
- gene for insulin is found in all cells but only activated in beta cells of pancreas
- stem cells differentiate into specialised cells
- during differentiation some genes are turned on and others off
- insulin is a hormone that regulates the amount of glucose in blood
- pancreatic beta cells have sensors that detect glucose level in blood
- an increase in glucose will increase transcription of mRNA of insulin
- the site of transcription of insulin is in the pancreatic beta cells
- gene transcription is regulated by proteins that bind to specific base sequence in DNA
- regulatory proteins are specific to the gene they regulate
6
Q
outline the process of DNA profiling (4)
A
- sample of DNA obtained from person
- PCR used to amplify DNA
- using Taq DNA polymerase
- tandem repeats amplified
- gel electrophoresis used to separate DNA into bands
- separation according to length of fragments
- pattern of bands/ numbers of repeats is the profile
7
Q
explain how polypeptides are produced by the process of translation (8)
A
- mRNA is translated
- mRNA binds with ribosome
- tRNA-activating enzymes attach specific amino acid to tRNA
- anticodon of 3 bases on tRNA
- start codon
- tRNA carrying first amino acid binds to P
- anticodon on tRNA binds to codon on mRNA
- complementary base pairing
- tRNA for next codon binds to A site
- peptide bond forms between amino acids at P and A sites
- ribosome moves along mRNA to next codon in 5’ to 3’ direction
- tRNA released from E
- process repeats to elongate the polypeptide until stop codon is reached
- release of polypeptide and mRNA at stop codon
8
Q
distinguish between transcription and translation (4)
A
- DNA is transcribed and mRNA is translated
- transcription produces RNA and translation produces polypeptide
- RNA polymerase used in only in transcription and ribosomes only in translation
- transcription in the nucleus of eukaryotes and translation in the cytoplasm
- tRNA needed for translation but not transcription
- nucleotides linked in transcription and amino acids in translation
9
Q
distinguish between transcription and translation (4)
A
- DNA is transcribed and mRNA is translated
- transcription produces RNA and translation produces polypeptide
- RNA polymerase used in only in transcription and ribosomes only in translation
- transcription in the nucleus of eukaryotes and translation in the cytoplasm
- tRNA needed for translation but not transcription
- nucleotides linked in transcription and amino acids in translation
10
Q
explain the control of gene expression in eukaryotes (8)
A
- mRNA conveys genetic information from DNA to the ribosomes where it guides polypeptide production
- gene expression requires the production of specific mRNA through transcription
- most genes are turned off/ not being transcribed at any one time
- some genes are only expressed in certain cells
- transcription factors can increase/ decrease transcription
- hormones/ chemical environment of cell can affect gene expression
- transcription factors may prevent or enhance the binding of RNA polymerase
- nucleosomes limit access of transcription factors to DNA
- DNA methylation/ acetylation appears to control gene expression
- DNA methylation patterns are inherited
- introns any contain positive or negative gene regulators
11
Q
explain DNA replication (8)
A
- helicase unwinds the double helix
- gyrase relieves strains during uncoiling
- helicase separates the two strands of DNA
- each single strand acts as a template for a new strand
- DNA polymerase III can only add nucleotides to the end of an existing chain
- primase adds RNA primer
- DNA polymerase III adds nucleotides in a 5’ to 3’ direction
- complementary base pairing
- DNA polymerase moves towards the replication fork on leading strand and away from it on the lagging strand
- continuous on the leading strand and discontinuous on the lagging strand
- DNA polymerase I replaces RNA primers with DNA
- ligase going the fragments together
