Protein synthesis and selection Flashcards
What is a mutation? (1)
Change to the DNA base sequence
How and when do mutations occur? (2)
Randomly and spontaneously
During DNA replication
Why might a mutation not lead to change in the amino acid sequence (2)
Genetic code is degenerate (mutation may end up coding for the same amino acid as the original triplet)
Mutation may occur in an intron
What is a silent mutation?
Alters a base but does not change the amino acid coded for (the code is degenerate)
What is a substitution mutation? (2)
One nucleotide takes place of another - usually leads to no change in the amino acid sequence
What is an addition mutation? (1)
When one or more bases are added
What is a deletion mutation? (2)
One nucleotide is removed from a gene or DNA sequence - harmful and significant because it leads to a frameshift which means the entire amino acid sequence will be different
What does an addition/deletion mutation cause? (1)
Results in alteration of the base triplets from the mutation onwards and so is known as a frameshift
How do mutations lead to non-functional proteins? (5)
Alter the primary structure of polypeptides
So alter the secondary structure and change the positions of the weak hydrogen bonds affecting alpha helixes and beta pleated sheets
Alter the tertiary structure (change positions of H-bonds, ionic bonds and disulphide)
Alter the binding site of proteins and make them non-functional
What are mutations responsible for in the forces of natural selection and in speciation? (1)
Genetic diversity of populations
What are mutagenic agents? (1)
Outside factors that increase the rate of spontaneous mutation
Examples of mutagenic agents? (3)
High energy ionizing radiation (X-rays, UV light, gamma rays)
DNA reactive chemicals (benzene, hydrogen peroxide)
Biological agents such as some viruses and bacteria
What is a chromosomal mutation and what does it cause? (2)
Mutations that produce changes in whole chromosomes
Causes chromosome non-disjunction
What is chromosome non-disjunction? (2)
When chromosomes fail to separate correctly in meiosis, resulting in gametes with one more or less chromosome than normal.
What is inversion mutation? (1)
When a segment of bases is reversed end to end
What is duplication mutation? (2)
Doubling of a part of chromosome or of an entire chromosome or even the whole genome
When one or more bases are repeated
What is translocation mutation? (1)
When groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes
Moves a segment from one chromosome to another, nonhomologous one
What is a phenotype? (1)
The expression of the genetic constitution and its interaction with the environment
What is a genotype? (1)
Genetic makeup of an organism (all the alleles an organism has)
What is genetic diversity? (1)
The number of different alleles in a population
What advantage does high genetic diversity provide? (2)
Ability to adapt to a change in environment
Allows natural selection to occur
What are selection pressures? (1)
External agents which affect an organism’s ability to survive in a given environment
Describe natural selection (6)
Variation due to mutation
Different environmental/selection pressures
Selection for advantageous allele
Differential reproductive success/(selected) organisms survive and reproduce
Leads to change in allelic frequency
Occurs over a long period of time
When does stabilising selection occur? (1)
When environment is stable/the same
What is stabilising selection? (2)
When the environment favours the average (most common characteristic - eliminates extremes)
Reduces diversity and reduces opportunity for evolutionary change
What is directional selection and when does it occur? (2)
Favour an extreme phenotype
Occurs when environmental conditions change
What does a mean in population represent? (1)
Optimum phenotype for existing conditions
What is disruptive selection? (1)
Favours 2 extreme phenotypes
What is evolution by natural selection? (1)
Change in allelic frequencies within a population
What is the genome? (1)
Complete set of genetic information contained in the cell of an organism
What is a proteome? (1)
Full range of proteins that a cell is able to produce
What does loci mean? (1)
Position of a gene within the chromosome
What is a gene? (1)
DNA base sequence coding for a single polypeptide
What are exons and introns? (2)
Exons - sequence of nucleotides that code for the amino acid sequence
Introns - non-coding sequence of nucleotides
Where are introns found? (1)
Between exons within genes
Describe transcription (5)
DNA helicase breaks hydrogen bonds so that the strands separate
Only one strand acts as a template
RNA nucleotides attracted to exposed bases
Adenine - Uracil and Guanine - Cytosine
RNA polymerase joins adjacent nucleotides together forming phosphodiester bonds through condensation reaction
pre-mRNA spliced to remove introns
Describe translation (8)
mRNA binds to ribosome
Ribosome finds the start codon
Only 2 codons can fit the ribosome at one time
tRNA with complementary anticodon binds to the codon on mRNA
tRNA brings a specific amino acid
Catalyses formation of peptide bonds between amino acids, held by tRNA, using energy from ATP
tRNA released as ribosomes move along
Ribosome releases polypeptide when the stop codon is reached
What are ribosomes made of? (2)
rRNA and ribosomal proteins
What is the genetic code? (2)
Order of bases on DNA
Consists of codons
Identify and describe the features of the genetic code (3)
Non-overlapping - Each base is read once in a triplet
Degenerate - more than one triplet can code for the same amino acid
Universal - The same 3 bases on mRNA/DNA code for the same amino acids in all organisms
What is a population? (1)
All the organisms of a particular species that live in the same habitat
Give and explain an example of directional selection (3)
Antibiotic resistance
Bacteria with a mutation allowing them to survive in the presence of antibiotics will reproduce
Frequency of the allele will increase and the population will shift to have greater antibiotic resistance
Give and explain an example of stabilising selection (2)
Birth weight
Babies that weigh around 3kg are more likely to survive than those at lower or higher weights
Define a niche (1)
Role of a species within its environment
Species sharing the same niche will compete with each other
What are the three types of adaptation and give an example of each (6)
Anatomical (changes to body structure) - oily fur
Physiological (changes to bodily processes) - venom production
Behavioural (changes to actions) - hibernation
