Protein synthesis and selection Flashcards
What bonds are nucleotides joined by
phosphodiester bonds
Structures in DNA nucleotide
phosphate group
deoxyribose sugar
base
purine bases
adenine
guanine
pyrimidine bases
thymine
cytosine
what is adenine matched with
thymine
what is cytosine matched with
guanine
difference between eukaryotic DNA and prokaryotic DNA
linear vs circular
histones vs no histons
introns vs no introns
RNA nucleotide contents
phosphate groups
ribose sugar
base
how is mRNA different to DNA
double stranded vs single stranded
longer vs shorter
GC + AT vs GC + AU
hydrogen bonds vs no hydrogen bonds
introns vs no introns
mRNA characteristics
single stranded
shorter than DNA
GC + AU
tRNA characteristics
1 polynucleotide chain
75 nucleotides
single stranded
hydrogen bonds
amino acid attachment site
anticodon
name the 2 protein synthesis processes
transcription
translation
Transcription steps
-DNA helicase breaks H bonds between two strands and unwinds DNA double helix
-DNA strands separate
-only 1 strand used as a template
-free nucleotides bind to exposed DNA bases via complementary base pair rules on template strand
-U to A + C to G
-RNA polymerase joins RNA nucleotides together by forming phosphodiester bonds
-introns are removed via splicing to produce mature mRNA
mRNA passes out of nucleus via nuclear pore to ribosome
translation steps
-mRNA binds to ribosome
-mRNA has two binding sites
-allows tRNA with anticodons to bind
-catalyses formation of peptide bond between two amino acids
-moves along to next codon
3 ways to describe genetic code
-universal
-non overlapping
-degenerate
what does universal genetic code mean
the same 3 bases on DNA code for the same amino acid in all organisms
what does non-overlapping genetic code mean
each base is only 1 triplet code
what does degenerate genetic code mean
more than 1 triplet DNA codes for an amino acid
mutation definition
change to a single base in DNA base sequence of a gene
mutations occur randomly and could happen spontaneously
result of mutation
-may result in a change in the PRIMARY STRUCTURE OF POLYPEPTIDES sequence of amino acids in the polypeptide chain
-may alter the SECONDARY STRUCTURE by changing the position of the weak hydrogen bonds affecting the alpha helices and beta-pleated sheets
-may alter the TERTIARY STRUCTURE by changing the position of the weak Hydrogen, Ionic bonds between the R groups of amino acids and the Disulphide bonds
-and may alter the ACTIVE site of enzymes and make the protein non-functional.
silent mutation
-mutation does not change the amino acid coded
-so will have no effect on the polypeptide chain
-as DNA code is degenerate
substitution mutation
a substitution of a base with another base
what happens if there is a mutation for the STOP codon
-cause the growing polypeptide chain to terminate prematurely
-may not be able to perform its intended function
addition/deletion mutations
-nucleotide added or deleted
-alteration of base triplet from the mutation onward
-reading frame has been shifted and is known as a frameshift
-addition/deletion that occurs towards the end of a sequence of bases would have a lesser effect but still alter some amino acids at the end of a gene
mutagenic agents
- high energy ionising radiation x-ray and gamma ray
- DNA reactive chemicals such as benzene or bromine
- biological agents such as virus and bacteria
chromosomal mutations
-chromosome nondisjunction
-too many chromosomes produced
inversion mutation
-when a segment of bases is reversed end to end
duplication mutation
-doubling of a part of a chromosome OR of an entire chromosome OR even the whole genome
translocation mutations
when a group of base pairs relocate from one area of the genome to another
usually between non-homologous chromosomes
allele definition
different versions of the same gene
genetic diversity definition
number of different alleles of genes in a population
natural selection definition
-organisms that are better adapted to their environment survive and reproduce
-in greater numbers
-resulting in the increase of the frequency of the advantageous allele within the population
stabilising selection and example
-occurs in all populations where environment is stable.
-selection pressure at both ends of distribution.
-favours the average.
-tends to eliminate extremes.
-reduces variability and the size of the range within population.
-reduces opportunity for evolutionary change
-birth mass
directional selection and example
-mean in population represents optimum phenotype for existing conditions
-environmental change produces new selection pressure that favours an extreme phenotype
-changed conditions, favour allele combination necessary for survival
-some organisms will possess the new optimum phenotype (allele combination)
-over time, selection means this allele combination will predominate
-the mean phenotype will shift
-eg. thicker fur for mice
disruptive selection
-is the opposite of stabilising selection
-environmental has selection pressures that favour 2 extreme phenotypes
-when conditions change the optimum phenotypes necessary for survival will also change
-some organisms will possess the new extreme optimum phenotypes
-over time selection means these 2 extremes will dominate and the mean will shift in both directions of extremes
-it is the least common type of selection but it is the most important in evolution
what are viable counts of bacteria
counts living cells only
