DNA, Mutations, Genes & Chromosomes 4.1 Flashcards
What is a mutation? (1)
An alteration to the DNA base sequence
Arises spontaneously during DNA replication
What are addition and deletion mutations? (1)
One or more nucleotides (bases) are inserted OR deleted from DNA base sequence
What is a substitution mutation? (1)
Where one nucleotide base is replaced by another in DNA base sequence
What is a duplication mutation? (1)
One or more nucleotides (bases) duplicate and repeat
What is an inversion mutation? (1)
A group of nucleotide bases separate from the DNA sequence and rejoin in reverse order/are flipped
What is a translocation mutation? (1)
A group of nucleotide bases separate from DNA sequence and are inserted into DNA on a different chromosome
Which DNA base mutations are most likely to have a significant impact & why? (2)
Insertion, Deletion, Duplication, Translocation
- All produce a frameshift, entire amino acid sequence produced will be different
Which mutations are most likely to have a smaller impact and why? (2)
Substitution and Inversion
- Only alter a few DNA triplets, so amino acid sequence may not be affected as degenerate (more than one codon/triplet for each amino acid)
Is mutation resulting in a change to amino acid sequence always harmful? (2)
No; may be no change in protein produced /protein has little effect
May be beneficial - basis for evolution and natural selection
What is a mutagenic agent? Give examples
Factors that increase the rate of gene mutation.
Ionising radiation = GAMMA, UV and X-RAY
Chemical mutagens = alcohol and benzene
What are the three components of nucleic acids?
a pentose sugar, a phosphate group, an organic base
Describe the structure of DNA
Deoxyribose sugar
Phosphate group
Organic bases (A-T, C-G)
- Double stranded
- Hydrogen bonds between bases form helix shape
Describe the role of DNA (1)
Carries an organism’s genetic material, determines inherited characteristics
Describe the structure of RNA
Single stranded
Ribose sugar
Phosphate group
Organic bases (A-URACIL, C-G)
Describe the role of RNA (1)
Transfers genetic information from DNA to ribosomes for protein synthesis.
Which bases are purine and which are pyrimidine?
Purine (double ring) = adenine + guanine
Pyrimidine (single ring) = cytosine + thymine/uracil
What are the features of the genetic code? (3)
Non-overlapping = Each codon is only read once
Universal = same bases and sequences used by all species
Degenerate = more than one triplet codes for the same amino acid (64 combinations to 20 amino acids)
What is a gene?
A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide
(also codes for functional RNA)
What is an allele?
Different versions of the same gene, found at the same locus of a chromosome (position of gene on DNA molecule)
What are exons and introns?
Exons = Regions of DNA that code for amino acid sequences
Introns = Do not code for anything
Where are introns found?
Between exons within genes
