Lecture 10 - The Genetic Code and Mutations

What is the genetic code?

nucleotide instructions that determines amino acid sequence of protein

What is a codon?

sequence of 3 nucleotides

How many possible codons are there?

64 codons

Why are 64 codons needed?

4 nucleotide bases but 20 amino acids

What is a reading frame?

how nucleotides are grouped into 3 base codons

What does it mean that the genetic code is redundant?

most amino acids have more than one codon

What is wobble?

third codon can tolerate some base pairing differences

What is the start codon?

aug, starts translation, codes for methionine

What are the three stop codons?

uaa, uag, uga

What do stop codons do?

stop translation, do not code for an amino acid

Is the genetic code universal?

yes, shared by most organisms

What is a mutation?

permanent change in dna sequence

How can mutations affect proteins?

change protein structure or function

What are two ways mutations can arise?

dna replication errors, mutagens

What is a point mutation?

change involving one base pair

What is a nucleotide substitution?

one base pair replaced by another

What are the three possible effects of a substitution?

silent, missense, nonsense

What is a silent mutation?

codon changes, amino acid stays the same

What is a missense mutation?

different amino acid is produced

What is an example of a missense mutation?

sickle cell disease, glutamic acid to valine

What is a nonsense mutation?

creates a stop codon

What happens when a stop codon is created early?

translation stops early, shorter protein

What is an insertion?

nucleotide pair added

What is a deletion?

nucleotide pair removed

When does an insertion or deletion cause a frameshift?

nucleotides added or removed is not a multiple of 3

What is a frameshift mutation?

mutation that changes the reading frame

What are three causes of mutations?

dna replication errors, uv light and x rays, spontaneous chemical reactions in cells

What is excision repair?

enzymes detect and repair damaged dna

What types of DNA damage can be repaired?

incorrectly paired nucleotides, altered nucleotides, chemical damage to dna bases

What does a nuclease do during DNA repair?

remove damaged section of dna