DNA Flashcards
Draw and label a single DNA nucleotide
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 / unzip;
may appear in the same feature
- Two strands, so both can act as templates;
may appear in the same feature
- Complementary base pairing allows accurate replication;
The enzymes DNA helicase and DNA polymerase are involved in DNA replication.
Describe the function of each of these enzymes.
DNA helicase _______________________________________________________
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DNA polymerase _____________________________________________________
DNA helicase – (unwinding DNA and) breaking hydrogen bonds / bonds between chains / bases / strands;
- DNA polymerase – joins (adjacent) nucleotides OR forms phosphodiester bond / sugar-phosphate backbone;
Adenosine triphosphate (ATP) is a nucleotide derivative.
Contrast the structures of ATP and a nucleotide found in DNA to give two differences
ATP has ribose and DNA nucleotide has deoxyribose;
- ATP has 3 phosphate (groups) and DNA nucleotide has 1 phosphate (group);
- ATP – base always adenine and in DNA nucleotide base can be different / varies;
Give one advantage of DNA molecules having two strands.
stability / protects bases / replication;
Describe how DNA is replicated
Strands separate / H-bonds break;
- Q Neutral: strands split
- Accept: strands unzip
- DNA helicase (involved);
- Both strands / each strand act(s) as (a) template(s);
- (Free) nucleotides attach;
- Neutral: bases attach
- Accept: nucleotides attracted
- Complementary / specific base pairing / AT and GC;
- DNA polymerase joins nucleotides (on new strand);
- Reject: if wrong function of DNA polymerase
- H-bonds reform;
- Semi-conservative replication / new DNA molecules contain one old strand and one new strand;
Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA.
Circular / non-linear (DNA);
Accept converse for eukaryotic DNA
Ignore: references to nucleus, binary fission, strands and plasmids
- Not (associated) with proteins / histones;
Accept does not form chromosomes / chromatin
- No introns / no non-coding DNA.
The table shows the percentage of each base in the DNA from three different organisms.
Organism
Percentage of each base in DNA
Adenine
Guanine
Thymine
Cytosine
Human
30.9
19.9
29.4
19.8
Grasshopper
29.4
20.5
29.4
20.7
Virus
24.0
23.3
21.5
31.2
(i) Humans and grasshoppers have very similar percentages of each base in their DNA but they are very different organisms.
Use your knowledge of DNA structure and function to explain how this is possible.
Have different genes;
Reject: different alleles
- (Sobases / triplets) are in a different sequence / order;
Accept: base sequence that matters, not percentage
- (So) different amino acid (sequence / coded for) / different protein / different polypeptide / different enzyme.
The DNA of the virus is different from that of other organisms. Use the table above and your knowledge of DNA to suggest what this difference is. Explain your
answer.
there percentages of complementary DNA bases dont add up to be equal
Virus DNA)
- A does not equal T / G does not equal C;
Accept: similar for equal
Accept: virus has more C than G / has more A than T
- (So) no base pairing;
- (So) DNA is not double stranded / is single stranded
The gene for this polypeptide contains more than this number of bases.
Explain why
Some regions of the gene are non-coding / introns / start / stop code / triplet / there are two DNA strands;
Allow addition mutation
Explain why the replication of DNA is described as semi-conservative.
each strand copied / acts as a template;
(daughter) DNA one new strand and one original / parent strand
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.
Condensation (reaction)/loss of water;
- (Between) phosphate and deoxyribose;
- (Catalysed by) DNA polymerase;
The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus.
In chloroplasts
Must be comparative statements.
Accept alternatives in context of nuclear DNA
1. DNA shorter;
Accept smaller
2. Fewer genes;
3. DNA circular not linear;
Accept DNA in a loop not linear
Accept no chromosomes (in chloroplast) unlike nucleus
4. Not associated with protein/histones, unlike nuclear DNA;
5. Introns absent but present in nuclear DNA;
