Paper 2 - Inheritance Flashcards
Describe a DNA molecule
- 2 strands coiled to form a double helix
- The strands are linked by a series of paired bases: adenine (A) with thymine
(T), and cytosine (C) with guanine (G)
Describe an RNA molecule
- Single-stranded
- Contains uracil (U) instead of thymine (T)
What are the stages of protein synthesis?
Transcription and translation
What are the stages of Transcription?
- Section of DNA molecule unwinds and unzips
- Bases are exposed along the template strand
- RNA nucleotides line up along the template strand according to complementary base pairing rules
- RNA nucleotides link together to form mRNA
- mRNA leaves the nucleus through a pore to the cytoplasm
- mRNA goes to the ribosome
- DNA Helix zips up again
What are the stages of Translation?
- mRNA binds to the ribosome
- The ‘Start’ codon is always AUG which codes for amino acids methionine to tRNA with complementary UAC anticodon of this tRNA binds to the next codon of mRNA
- A bond forms between methionine and the 2nd amino acid
- The first tRNA is released, ribosomes shift along by one codon and a new tRNA binds etc…
- This continues until the ‘stop’ codon is reached and the protein is released
What is the role of mRNA?
- mRNA is a copy of the gene
- mRNA transports RNA nucleotides to the ribosome
What is the role of a ribosome?
- To move along the RNA and read 3 bases (1 codon) at a time
- So that the tRNA with the complementary bases will come in and the amino acid will be attached to the tRNA
What is the role of tRNA
- To deliver the anticodons that complement the codons on the RNA in the ribosome
- Once bonded, the tRNA gets released
What is the role of a codon?
To receive the complementary anticodon from tRNA to form an amino acid
What is the role of an anticodon?
To deliver the complementary bases from tRNA to the codon on the RNA to form an amino acid
What are the rules of complementary base pairing in DNA?
- Adenine (A) and Thymine (T)
- Cytosine (C) and Guanine (G)
What are the rules of complementary base pairing in RNA?
- Adenine (A) and Uracil (U)
- Cytosine (C) and Guanine (G)
What is a codon?
A set of 3 bases on the RNA strand
What is an anticodon?
A set of 3 bases on the tRNA strand that complement a set of 3 bases on the RNA strand (the codon)
What happens when the ribosome reaches the ‘stop’ codon?
- The original gene sequence from the DNA has been fully replicated
- The Protein is released
What is codominance?
When both alleles are dominant
How can a change in DNA affect the phenotype by altering the sequence of amino acids in a protein?
- Random mutation can change the DNA sequence via duplication, deletion, substitution or inversion
- Creates a new codon so anticodon is no longer complementary
- Codes for and therefore creates incorrect amino acid
- If the amino acid sequence in different, the protein structure will change
- If that protein is an enzyme, the mutation will change the shape of the active site so it will no longer be complementary to the substrate
What, if any, effects can genetic mutations have?
Most genetic mutations have no effect on the phenotype, some have a small effect and rarely do they have a significant effect
How could the incidence of mutations be increased?
By exposure to :
- Ionising radiation such as, gamma rays, x-rays and UV rays
- Some chemical mutagens such as chemicals in tobacco
