3.4.1 DNA, genes and chromosomes Flashcards
What is a DNA triplet?
A sequence of three bases in a gene.
What is an intron?
A section of a gene that doesn’t code for amino acids.
What are non-coding repeats?
A region of multiple repeats, outside of genes, that don’t code for amino acids.
What is a locus?
A locus refers to the same fixed positions between chromosomes in a homologous pair.
What is a gene?
A sequence of DNA bases that codes for either a polypeptide or functional RNA.
What determines the order of amino acids in a particular polypeptide?
The order of bases in a gene.
Describe how DNA is stored in eukaryotic cells.
[5 marks]
Any five points from:
- In the nucleus of eukaryotic cells, DNA is stored as chromosomes.
- It is linear.
- It is wound around proteins called histones.
- Mitochondria and chloroplasts in eukaryotic cells also contain DNA.
- In mitochondria and chloroplasts, the DNA is short and circular.
- The DNA in mitochondria/chloroplasts is not associated with histones.
A scientist is studying a DNA sequence that is made up of 3800 nucleotide pairs. Exons account for 672 of the nucleotide pairs. Introns account for 3128 of the nucleotide pairs. The sequence codes for a section of a polypeptide. How many amino acids will make up this section of the polypeptide?
[2 marks]
672 ÷ 3 = 224 amino acids
Only the exons code for amino acids.
Describe how DNA is stored in prokaryotic cells.
- Prokaryotes carry DNA as chromosomes…
- …but the DNA molecules are shorter and circular.
- DNA isn’t wound around histones.
- It condenses to fit in the cell by supercoiling.
What is a cell’s ‘genome’?
The complete set of genes in the cell.
What is a cell’s ‘proteome’?
The full range of proteins that the cell is able to produce.
What is the genetic code?
The sequence of base triplets (codons) in mRNA which code for specific amino acids.
Why is the genetic code described as degenerate?
- There are more possible combinations of triplets than there are amino acids.
- Some amino acids are coded by more than one base triplet.
Why is the genetic code described as universal?
The same specific base triplets code for the same amino acids in all living things.
Why is the genetic code described as non-overlapping?
- Each base triplet is read in sequence, separate from the triplet before it and after it.
- Base triplets don’t share their bases.
