3.4.1 DNA, genes and chromosomes Flashcards
What is the structure of DNA in prokaryotic cells?
Short circular DNA not associated with proteins
What is the structure of DNA in the nucleus of eukaryotic cells?
Very long linear DNA associated with proteins called histones
What do DNA and histones form in eukaryotic cells?
A chromosome
What is the structure of DNA in mitochondria and chloroplasts of eukaryotic cells?
Short circular DNA not associated with proteins
What is a gene?
A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA
What is the fixed position a gene occupies on a DNA molecule called?
A locus
What is a triplet?
A sequence of three DNA bases that codes for a specific amino acid
What does it mean that the genetic code is universal?
The same triplet codes for the same amino acid in all organisms
What does it mean that the genetic code is non-overlapping?
Each base is read only once and in triplets
What does it mean that the genetic code is degenerate?
More than one triplet can code for the same amino acid
In eukaryotes what does much of the nuclear DNA not code for?
Polypeptides
What are non-coding multiple repeats of base sequences between genes called?
Non-coding multiple repeats
In a gene what are exons?
Sequences that code for amino acid sequences
In a gene what are introns?
Non-coding sequences that separate exons
Describe how a gene is a code for the production of a polypeptide.
Do not include information about transcription or translation in your answer.
- Because) base/nucleotide sequence;
- (In) triplet(s);
- (Determines) order/sequence of amino acid sequence/primary structure (in polypeptide);
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;
Reject if DNA polymerase joins AT/GC OR complementary nucleotides/bases OR forms hydrogen bonds
DNA – Structure related to function (7)
- stable due to numerous hydrogen bonds so can be passed on from generation to generation;
- weak hydrogen bonds between strands are easily broken for DNA replication or protein synthesis;
- large so can carry a lot of genetic information;
- base pairs are contained within the helix and held in place by the strong sugar-phosphate backbone;
- complementary base pairs allow the synthesis of an identical daughter molecule;
- 2 strands so both can act as templates;
- helical shape means that it can be coiled so compact for storage
DNA – Degenerate and Non-overlapping (2)
- Degenerate: more than one (base) triplet for each amino acid;
- Non-overlapping: each base is part of only one triplet;
Comparing mRNA and tRNA (3)
- mRNA longer;
- mRNA is a straight molecule but tRNA is a folded molecule/clover-leaf shaped molecule;
- mRNA contains hydrogen bonds but tRNA has hydrogen bonds;
Which two molecules are ribosomes made from?
(2)
- One of RNA/ribonucleic acid(s)/nucleotide(s)/nucleic acid(s)/rRNA/ribosomal RNA/ribosomal ribonucleic acid;
- One of protein(s)/polypeptide(s)/amino acid(s)/ peptide(s)/ribosomal protein
Differences between prokaryotic DNA and Eukaryotic DNA (5)
(eukaryote v prokaryote
- (Associated with) histones/proteins v no histones/proteins;
- Linear v circular;
- No plasmids v plasmids; Do not credit if suggestion that prokaryotic DNA only exists as plasmids.
- Introns v no introns;
- Long(er) v short(er);
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 Accept: DNA/code/triplets are degenerate Reject: codons (as question states within genes)
- Occurs in introns /non-coding sequence;
Reject: codons (as question states within genes) Ignore junk DNA Reject: multiple repeats
