12.4 Protein Synthesis Flashcards
eukaryotes DNA
- has ends - linear
- very long
- human DNA 3.2 B nucleotides
- histone proteins (package it into cells wraps it around proteins)
- 1 strand contains genes
- exons and introns
prokaryotes DNA
- dont contain a nucleus
- shorter DNA
- eukaryotic mitochondria + chloroplasts
- DNA similar to eukaryotes
- 1 strand contains genes
- exons but no introns
exon definition
coding DNA base sequence found within a gene
intron definition
non-coding DNA base sequence found within a gene
similarities in prokaryotic DNA and eukaryotic DNA
- P + E DNA have similar organelles
- both made from nucleotides
differences in prokaryotic DNA and eukaryotic DNA
- E is linear whereas P is circular
- E is associated with histone proteins whereas P is not associated with histone proteins
- E contains introns whereas P does not contain introns
4 types of RNA
- mRNA
- tRNA
- rRNA
- RNAi
codon definition
a sequence of 3 bases on mRNA that codes for a specific amino acid
anticodon definition
a sequence of 3 nucleotide bases at one end of a tRNA molecule that is specific to an mRNA codon
mRNA characteristics
- single stranded
- complementary copy of a single gene from the TEMPLATE strand of DNA
- shorter than DNA
- sequence of bases on mRNA complementary to sequence of bases of the gene its copying
- G-C and A-U
- codons
differences in DNA and mRNA
- DNA double stranded whereas mRNA single stranded
- DNA longer whereas mRNA shorter
- thymine DNA whereas uracil mRNA
- deoxyribose DNA whereas ribose mRNA
- H bonds DNA whereas no H bonds mRNA
- introns DNA whereas no introns mRNA
tRNA characteristics
- polynucleotide chain of about 75 nucleotides
- single stranded
- cloverleaf structure held by H bonds
- amino acid attachment site where only a specific amino acid binds
- anticodons
- role is to carry a specific amino acid to the ribosome
what does the anticodon do on the tRNA molecule
- anticodon is specific to the amino acid carried by the tRNA and is complementary to the codon on the mRNA
- the anticodon base pairs with the codon on the mRNA molecule
genome definition
complete set of genes in a cell / complete base sequence of all the DNA from a cell of an organism
proteome definition
full range of proteins that a cell is able to produce
loci definition
position of a gene within chromosome
allele definition
a different version / form of a gene
gene definition
a DNA base sequence that codes for a sequence of amino acids in a polypeptide
2 processes involved in protein synthesis
transcription and translation
transcription definition
making a copy of the base sequence of a specific gene (DNA) onto the base sequence of an mRNA molecule
translation definition
the conversion of the base sequence of mRNA (at a ribosome) into the specific amino acid sequence of a polypeptide chain (primary structure)
transcription of prokaryotes occurs in the…
cytoplasm
transcription of eukaryotes occurs in the…
nucleus
how does pre-mRNA turn into mature MRNA
its ‘spliced’
what is the process of ‘splicing’
introns removed and the exons are re-joined
stop codon
AUG
key processes of transcription
- forming a pre-mRNA molecule from the DNA
- removing introns to create a mature mRNA molecule
describe transcription
1 (DNA helicase) H bonds are broken so strands separate
2 only one DNA strand acts as template
3 RNA nucleotides are attracted to the exposed bases
4 (attraction) according to base pairing rule A-U, C-G
5 RNA polymerase joins (RNA) nucleotides together forming phosphodiester bonds through condensation reactions
6 Pre-mRNA spliced to remove introns (in eukaryotes)
what are ribosomes made from
rRNA and ribosomal proteins
what does RER stand for
rough endoplasmic reticulum
describe translation
1 mRNA binds to ribosome
2 ribosome finds the START codon
3 idea of 2 codons / binding sites
4 (allows) tRNA with complementary anticodons to bind / associate with codon
5 (catalyses) formation of peptide bond between amino acids (held by tRNA molecules) using energy from ATP
6 tRNA released as ribosome moves along (mRNA to the next codon) / translocation described
7 ribosome releases polypeptide into RER when the STOP codon is reached
3 bases on DNA
triplet
3 bases on mRNA
codon
3 bases on tRNA
anticodon
the genetic code characteristics
- universal
- non-overlapping
- degenerate
the genetic code is universal what does this mean
the same 3 bases on mRNA (codon) / DNA (triplets) code for the same amino acids in all organisms
the mechanism of transcription and translation are…
universal throughout all organisms
the genetic code is non-overlapping what does this mean
- each base is only part of 1 triplet (DNA) / codon (mRNA)
- during translation the ribosome reads each base only once in the codons on the mRNA - 1st 3 bases read, followed by 2nd 3 bases, then the 3rd 3 bases and so on in sets of 3
the genetic code is degenerate what does this mean
- more than 1 triplet (DNA) / codon (mRNA) codes for an amino acid
- 20 amino acids and 64 combinations of triplets / codons
- the 1st 2 bases are the most important when coding for amino acids
evidence for triplet codes
- 20 different amino acids and only 4 bases in any polynucleotide
- sequence of these bases determines the 20 different amino acids
- 4^1 = 4, 4^2 = 16, 4^3 = 64
Mutation definition
Any change to the DNA base sequence
Gene mutation definition
- Single-point mutation
- a change to a single base in the DNA base sequence of a gene.
When do gene mutations occur and happen
Occur Randomly and happen spontaneously
What would a mutation in DNA result in
A change in the primary structure of polypeptides, sequence of amino acids in the polypeptide chain
What MAY the consequence be of a mutation of DNA
- may alter the secondary structure (change the position of the weak H bonds affecting the alpha helices and beta-pleated sheets)
- may alter the tertiary structure (change the position of the weak H, ionic bonds between the R groups of amino acids and the disulphide bonds) and may alter the binding site or active site of enzymes and make the protein non-functional.
Where do mutations occur
During DNA replication
3 types of mutations
Substitution, deletion, addition
effect of substitution in the 3rd base
- wouldn’t alter the amino acid coded for (as the 3rd codon can either be A, C, T, G)
- silent mutation
- mutation doesn’t change the amino acid coded for -> no effect on polypeptide chain
- code is degenerate (more than 1 codon can code for an amino acid - the 3rd base can differ for some amino acids)
effect of substitution in the 1st base
- will change the amino acid sequence -> will alter the sequence of amino acids on the polypeptide chain -> may alter its specific tertiary structure / shape and function
effect of substitution from a triplet to a STOP codon
causes the growing polypeptide chain to terminate prematurely and may not be able to perform it’s intended function (depending how early the termination occurred)
addition / deletion mutations definition
1 full DNA nucleotide is gained or lost (within the gene)
result of an addition / deletion mutation
- results in an alteration of the base triplets from the mutation onwards
- frame shift occurs (the reading frame has been shifted to the right / left by 1 base)
effect of an early addition / deletion mutation in the sequence
more of the triplets coding for a polypeptide could be affected -> more of the amino acids would be altered
effect of an late addition / deletion mutation in the sequence
lesser effect -> would still alter some amino acids at the end of the gene
when do mutations occur
- spontaneously during DNA replication
- occur at a set rate (different for different species)
mutations definition
natural and random events and cause permanent changes to the DNA base sequence which is passed on to future generations
mutations are responsible for the genetic diversity of populations both in forces of…
natural selection and in speciation
mutations can be 3 things
- advantageous
- disadvantageous
- neutral
what do mutations often produce
organisms that are less well adapted to their environment and can alter cellular activities
mutation in gametes often proves…
fatal
mutagenic agents increase the rate of…
spontaneous mutation
3 mutagenic agents
- high energy ionising radiation
- DNA reactive chemicals
- Biological agents
what is high energy ionising radiation and what does it do
- X / gamma rays, alpha / beta particles
- damage the DNA molecule (bases) and chemicals that alter the DNA structure or interfere with DNA replication
what are DNA reactive chemicals and what do they do
- benzene, bromine, hydrogen peroxide
- nitrous acid can remove an NH2 group from cytosine in DNA, converting the bases to uracil
what are biological agents
some viruses and bacteria
what are chromosomal mutations
- within meiosis the cell divides -> each daughter cell contains 1 of each homologous chromosome
- this can go wrong -> daughter cells produced containing too many chromosomes
- a pair of homologous chromosomes may fail to separate during metaphase 1 or sister chromatids fail to separate during metaphase 2 (chromosome non-disjunction)
example of chromosome dis-junction
down syndrome caused by non-disjunction of chromosome 21 (when gametes fuse at fertilisation offspring has 3 copies of chromosome 21 rather than 2)
inversion mutations definition
when a segment of bases is reversed end to end
duplication mutations definition
a doubling of a part of a chromosome, of an entire chromosome, or even the whole genome
translocation mutations definition
when groups of base pairs relocate from 1 area of the genome to another, usually between non-homologous chromosomes
