DNA, genes and chromosomes Flashcards
What is a gene?
A base sequence of DNA that codes for the amino acid sequence of a polypeptide and functional RNA
Describe how a gene is a code for the production of a polypeptide.
The nucleotide sequence in the code are in triplets that determine the sequence of amino acids in the primary structure of a protein.
What is the locus?
The location of a particular gene on a chromosome.
What is an allele?
The different version of the same gene.
What is a chromatid?
One of the arms of the chromosomes.
What are homologous pairs of chromosomes?
Two chromosomes that are the same size and have the same genes but have different alleles.
How is DNA stored in eukaryotic cells?
DNA is stored as chromosomes inside the nucleus which are surrounded by proteins called histones that prevent the DNA from being tangled.
How is DNA stored in prokaryotic cells?
DNA is stored as chromosomes but the DNA molecules are short and circular. The DNA is not wrapped around histones, instead it supercoils to fit inside the cell.
What are non coding and coding genes called?
Non-coding: introns
Coding: Exons
What are introns and exons?
Introns:
- DNA sequence that do not code for amino acids and therefore polypeptide chains.
Exons:
- DNA sequence that code for amino acids.
How is the DNA found in chloroplasts and mitochondria similar to DNA found in prokaryotic cells.
- Short, circular, not wrapped around by histones.
What is a triplet and what does it code for?
A sequence of 3 DNA bases that code for a specific amino acid
What is the genetic code?
Sequence of bases in DNA that consist of triplets of bases.
a) How many amino acids does the genetic code have to be able to code for
b) how many bases are needed to make enough combinations to code for at least (answ to no. a) amino acids
a) 20 amino acids
b) 3 bases which makes 64 amino acids
What are features of the genetic code?
Degenerate:
- This is when more than one triplet codes for the same
amino acid, this reduces the number of mutations and if a mutation were to happen, it may still code for the same amino acid and therefore have no effect.
Universal:
- This is when the same triplet of bases code for the same amino acid in all organisms. (the genetic code will be the exact same whether its a plant, bacteria etc. This is an advantage because it allows genetic engineering to be possible.
Non-overlapping:
- This is when each base in a gene is only part of one triplet of bases that codes for one amino acid. Each codon or triplet of bases is read as a discrete unit. The triplets also don’t share any bases. This is an advantage because if a mutation occurs, it will only affect one codon and therefore one amino acid.
