19.1 Mutations and variation

Mutation?

a change in the sequence of bases in DNA

What can be disrupted if the mutation occurs within a gene?

Protein synthesis

What is the change in sequence caused by (3)?

substitution, deletion, or insertion of one or more nucleotides (or base pairs) within a gene

A Point mutation?

If only one nucleotide is affected

Substitution?

change of bases

What does the substitution of a single nucleotide change?

the codon in which it occurs

If the new codon codes for a different amino acid this will lead to change in what?

the primary structure of the protein

What does the degenerate nature of the genetic code mean?

that the new codon may still code for the same amino acid - leading to no change in the protein synthesised

What determines the impact of the new amino acid on the function of the protein?

The position and involvement of the amino acid in R group interactions

Example: if the protein is an enzyme and the amino acid plays an important role within the active site, what may happen to the protein?

the protein may no longer act as a biological catalyst

Deletion?

removal of bases

Insertion?

adds bases

What type of mutation does the insertion or deletion of a nucleotide, or nucleotides, lead to?

a frameshift mutation

A frameshift mutation?

a genetic change caused by the insertion or deletion of a number of nucleotides that is not a multiple of three, disrupting the normal reading frame of a gene

The reading frame of a sequence of bases?

The triplet code means that sequences of bases are transcribed (or read) consecutively in non-overlapping groups of three

What does each group of three bases correspond to?

one amino acid

What does the insertion or deletion of a nucleotide move?

the reading frame of the sequence of bases

What will a frameshift mutation change when it disrupts the reading frame?

will change every successive codon from the point of mutation

Many nucleotides are added or deleted, when will this not change the reading frame?

if the number of nucleotides changed is a multiple of three

Why will the number of nucleotides added or deleted being a multiple of 3 not cause a change in the reading frame?

Multiples of three correspond to full codons

Despite no change in the reading frame, why will the protein formed still be affected?

a new amino acid is added

Effects of mutation: Silent mutation?

most mutations are silent - do not change the proteins or activity of proteins​

The two reasons for why silent mutations occur?

either be because of the degenerate nature of the the genetic code OR because they occur in introns

Introns?

non - coding regions of DNA

Effects of different mutations: 3?

no effect, damaging and beneficial

No effect?

no effect on the phenotype of an organism

When will there be no effect on the phenotype of an organism?

because normally functioning proteins are still synthesised

Damaging?

the phenotype of an organism is affected in a negative way

When will the phenotype of an organism be affected in a negative way (2)?

because proteins are no longer synthesised or proteins synthesised are non-functional - This can interfere with one, or more, essential processes

Beneficial?

(rarely) a protein is synthesised that results in a new and useful characteristic

An example of a beneficial mutation (HIV immunity)?

a mutation in a protein present in the cell surface membranes of human cells means that HIV cannot bind and enter these cells - People with this mutation are immune to infection from HIV

What is the rate of mutation increased by?

mutagens

Mutagen?

a chemical, physical, or biological agent which causes mutations

Depurination?

The loss of a purine base

Depyrimidination?

the loss of a pyrimidine base

How does Depyrimidination and Depurination occur?

spontaneously

What can the absence of a base lead to?

the insertion of an incorrect base through complementary base pairing during DNA replication

Free radicals?

oxidising agents

What can free radicals affect?

the structures of nucleotides and also disrupt base pairing during DNA replication

Why are Antioxidants, such as vitamins A, C, and E (found in fruit and vegetables), anticarcinogens?

because of their ability to negate the effects of free radicals

Physical mutagens?

Ionizing radiations such as X-rays

Physical mutagens: what do Ionizing radiations such as X-rays do?

break one or both DNA strands — some breaks can be repaired but mutations can occur in the process

Chemical mutagens?

deaminating agents

Chemical mutagens: what do deaminating agents do?

alter bases in DNA (such as converting cytosine to uracil in DNA), changing the base sequence

Biological agents (3)?

alkylating agents, base analogs, viruses

Biological agents: what do alkylating agents do?

methyl or ethyl groups are attached to bases resulting in the incorrect pairing Of bases during replication

Biological agents: what do base analogs do?

incorporated into DNA in place Of the usual base during replication, changing the base sequence

Biological agents: what do viruses do?

viral DNA may insert itself into a genome, changing the base sequence

Effects of mutation: what do nonsense mutations result in?

a codon becoming a stop codon instead of coding for an amino acid

Effects of mutation: what does nonsense mutations causing a codon to become a stop codon instead of coding for an amino acid result in?

a shortened protein being synthesised which is normally non-functional

Effects of mutation: term for a protein or peptide that has been prematurely shortened?

Truncated AA (amino acid) sequence

Effects of mutation: what effect does nonsense mutations often have on the phenotype?

normally have negative Or harmful effects on phenotypes

Effects of mutation: what do missense mutations result in?

the addition of an incorrect amino acid (or amino acids) into the primary structure when the protein is synthesised

Effects of mutation: what does the result of missense mutations depend on?

the role the amino acid plays in the structure and therefore function of the protein synthesised

Effects of mutation: 3 ways the missense mutation can be?

silent, beneficial, or harmful

Effects of mutation: missense mutations - conservative?

similar amino acid coded for which has similar properties to the original - so effect is less severe​

Effects of mutation: missense mutations - non-conservative?

very different amino acid coded for which has different properties to the original - so more drastic effect and more likely to effect protein structure (may cause disease)​

Different mutations have a range of effects on proteins synthesised (3)?

amorph, hypomorph and hypermorph

Amorph?

mutation that results in the complete loss of gene function

Hypomorph?

mutation that results in a partial loss of gene function

Hypermorph?

mutation that results in an increase/addition in gene function

An example of something that is thought to be a result of a relatively recent mutation (milk)?

The ability to digest lactose (the sugar present in milk)

When do the majority of mammals in the world become lactose intolerant?

after they cease to suckle

Where is the ability to digest lactose found primarily in?

European populations who are more likely to farm cattle

What does the ability to drink milk and process lactose as an adult help to prevent?

diseases such as osteoporosis and also prevent individuals with the mutation from starving during famines

How has this mutation arisen?

spontaneously more than once (also been found in people in East Africa)