nucleic acids and genetic structure part 1 (Q&A) Flashcards
describe how mRNA is formed by transcription in eukaryotes ( 5 MARKS)
1) DNA helicase breaks down hydrogen bonds between complementary base pairs splitting the double helix strands
2) only one of those strands acts as a template.
3) complementary RNA joins with the bases on the template DNA strands and forms phosphodiester bonds between nucleotides with the help of RNA polymerase.
4) RNA polymerase works its way down the whole length of the template DNA strand until it reaches the end of the gene ( the stop codon )
5) mRNA strand has been formed/synthesised and RNA polymerase detaches from the DNA so the DNA can go back to its normal DNA helix structure.
6) mRNA then leaves the nucleus to take part in translation however before becomes spliced in RNA splicing to remove the introns in the strand ( the non coding DNA) and normal mRNA is formed
describe how a polypeptide is formed by translation of mRNA ( 6 marks )
- (mRNA attaches) to ribosomes
- (tRNA) anticodons (bind to) complementary (mRNA) codons;
- tRNA brings a specific amino acid;
- Amino acids join by peptide bonds; - this is catalysed by peptide-transferase.
- (Amino acids join together) with the use of ATP;
- tRNA released (after amino acid joined to polypeptide);
- The ribosome moves along the mRNA to form the polypeptide; - once this is correctly folded, it can carry out any function in the cell.
describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule
1.Condensation (reaction)/loss of water;
2. (Between) phosphate and deoxyribose;
3. (Catalysed by) DNA polymerase
Name the protein associated with DNA in a chromosome.
histone
describe how the separation of DNA strands occurs
1.DNA helicase;
- Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases
Describe the role of DNA polymerase in the semi-conservative replication of DNA.
1.Joins (adjacent DNA) nucleotides;
2. (Catalyses) condensation reactions
3. (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides)
Describe how an enzyme can be phosphorylated.
1.Attachment/association of (inorganic) phosphate (to the enzyme)
2. (Released from) hydrolysis of ATP
Some tumour cells contain higher than normal concentrations of cyclin D.
Use the graph above to suggest why higher than normal concentrations of cyclin D could result in a tumour.
- Shortens interphase
- faster cell division (mitosis)
- results in mass of abnormal cells
Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual.
- change in bases/nucleotides
- Results in the formation of new allele - recessive so does not influence phenotype
3.genetic code is degenerate
4.does change amino acid but does not change tertiary structure
- Results in change in polypeptide that positively changes the properties
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus.
DNA in chloroplast is :
1.shorter/smaller
2.circular (linear in nucleic DNA)
3.not associated with a histone
Give one other difference between the structure of a DNA nucleotide and the structure of an RNA nucleotide.
DNA contains deoxyribose where as RNA contains only ribose
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why.
Triplets code for same amino acid
Occurs in introns /non-coding sequence
Name the two scientists who proposed models of the chemical structure of DNA
and of DNA replication.
Watson and crick
Use your knowledge of semi-conservative replication of DNA to suggest:
the role of the single-stranded DNA fragments
the role of the DNA nucleotides
Role of single-stranded DNA fragments:
1. Template;
2. Determines order of nucleotides/bases
Role of DNA nucleotides
3. Forms complementary pairs / A – T, G - C
Describe the roles of iron ions, sodium ions, and phosphate ions in cells.
Iron ions
1. Haemoglobin binds/associates with oxygen
Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
Phosphate ions
6. Affects osmosis/water potential
7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in
nucleotides
The movement of substances across cell membranes is affected by membrane structure. Describe how.
- Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances
- Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances
3.Carrier proteins allow active transport
- Channel/carrier proteins allow facilitated diffusion/co-transport;
- Shape/charge of channel / carrier determines which substances move
The scientists determined the percentage of heart cells undergoing DNA replication by using a chemical called BrdU. Cells use BrdU instead of nucleotides containing thymine during DNA replication.
(b) Describe how BrdU would be incorporated into new DNA during semi-conservative replication. (5m)
- DNA helicase
- Breaks hydrogen bonds (between 2 DNA strands)
- BrdU complementary to adenine
- DNA polymerase joins (adjacent) nucleotides (to incorporate BrdU into the new DNA strand)
5.Phosphodiester bonds form between nucleotides
(c) Cells with BrdU in their DNA are detected using an anti-BrdU antibody with an enzyme attached.
Use your knowledge of the ELISA test to suggest and explain how the scientists identified the cells that have BrdU in their D(3m)
- Add antibody (anti-BrdU with enzyme attached)/DNA
- Wash (cells/DNA) to remove excess/unattached antibody
- Add substrate to cause colour change
Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA
- Weak / easily broken hydrogen bonds between bases allow two strands to separate
- Two strands, so both can act as templates
- Complementary base pairing allows accurate replication