Protein Synthesis Flashcards
What does a nucleotide consist of
A phosphate group
A pentose sugar
An organic base (ATCG)
What is DNA
Deoxyribose nucleic acid
A polymer of DNA nucleotides
A double helix consisting of two polynucleotide strands
Held together by hydrogen bonds
Between complementary base pairs (A and T/C and G)
Explain base pairing
A with T
-Purine Adenine always pairs with pyrimidine Thymine, forming two hydrogen bonds
C with G
-Purine Guanine always pairs with Pyrimidine Cytosine, forming three hydrogen bonds
Contrast eukaryotic and prokaryotic DNA
E is linear/P is circular
E is associated with histones/P is not
E contains introns/P does not
E is membrane bound (in nucleus)/P is free floating in the cytoplasm (not membrane bound)
E has no plasmids/P has plasmids
E is replicated in the nucleus/P is replicated in the cytoplasm
Similarities between eukaryotic and prokaryotic DNA
Contain exons
Phosphodiester bonds
Hydrogen bonds
Polymer of nucleotides
Structure of an RNA nucleotide
1 phosphate group
1 ribose sugar
1 organic/nitrogenous base
4 bases are Adenine, Uracil, Cytosine, Guanine
4 categories of RNA
mRNA; messenger, formed during transcription
tRNA; transfer, involved in translation
rRNA; ribosomal
RNAi; interfering, inhibits translation
What is mRNA
Messenger RNA
Single stranded polynucleotide chain
A complementary copy of a single gene from the template strand of DNA
Length depends on the number of bases that make up gene
Sequence of bases on mRNA are complementary to the sequence of bases on the gene its copying
What is a codon
3 bases on an mRNA strand
Complementary to a triplet of DNA strands
Codes for a specific amino acid
Stop codons tell RNA polymerase to stop transcription
Start codons tell RNA polymerase to start transcription
Stop codon
Tell RNA polymerase to stop transcription
Tell ribosome to detatch from mRNA
Start codon
Tell RNA polymerase to start transcription
Tell ribosome to initiate translation
Anticodon
Region of 3 bases on a tRNA molecule
Complementary to the codons on mRNA
Specific to the amino acid it carries
What is a triplet
Region of 3 bases on DNA
Coding for one specific amino acid
In a protein
What is transcription
Making a copy of the base sequence of a gene (DNA)
Onto the base sequence of an mRNA molecule
Beginning in the nucleus for Eukaryotes
What is translation
Conversion of the base sequence of mRNA
Into a specific sequence of amino acids
In a polypeptide chain (primary sturcture)
At a ribosome
Where does transcription occur in eukaryotes
Nucleus
Where does transcription occur in prokaryotes
Cytoplasm
What is an exon
Coding sequences within a gene of DNA
Code for amino acids in the sequence of a polypeptide (protein)
What is an intron
Non coding sequences of DNA found in a gene
Do not code for amino acids In the polypeptide chain of a protein
Spliced out in transcription
Not found in prokaryotes
Explain transcription
DNA helicase attaches to and unwinds DNA double helix
Hydrogen bonds broken by DNA helicase
Separating strands
One strand of DNA acts as template
Complementary free RNA nucleotides associate with exposed DNA bases on template strand via complementary base pairing
Adenine with Uracil and Cytosine with Guanine
RNA polymerase joins adjacent nucleotides by phospodiester bonds via condensation reactions
Pre mRNA spliced to remove introns
Forming mature mRNA
Exons spliced back together to form mRNA
Passes out of nucleus via nuclear pore to ribosome
Differences between DNA and mRNA
DNA double stranded/mRNA single stranded
DNA longer/mRNA shorter
DNA has thymine and no uracil/mRNA has uracil and no thymine
DNA is deoxyribose/mRNA is ribose
DNA has hydrogen bonding/mRNA has no hydrogen bonding
DNA has introns/mRNA does not
Similarities between DNA and mRNA
Both polymers of nucleotides
Both contain phosphodiester bonds between adjacent nucleotides
What is tRNA
Transfer RNA
Molecule that carries a specific amino acid into a ribosome so protein synthesis (translation) can occur
Has anticodons
Structure of tRNA
One polynucleotode chain of around 75 nucleotides
Clover leaf structure held together by hydrogen bonds
Amino acid attachment site where only a specific amino acid binds
Region of 3 bases called anticodons complementary to mRNA codon
Similarities between tRNA and mRNA
Both single stranded
Both contain uracil, ribose sugar and a phosphate group
Both polymers of RNA nucleotides
Both contain phosphodiester bonds between adjacent nucleotides
Differences between tRNA and mRNA
mRNA has codons and no anticodons/tRNA has no codons and anticodons
mRNA is linear/tRNA is clover leaf shape
mRNA has no hydrogen bonds/tRNA has hydrogen bonds
mRNA is longer/tRNA is shorter
mRNA has varying lengths depending on the gene/tRNA is always the same length
Genome
Complete base sequence of all the DNA from a cell of an organism
Proteome
Full range of proteins that a cell is able to produce
Loci
Position of a gene within a chromosome
Explain translation
mRNA binds/associates with ribosome
Ribosome moves along mRNA to find the start codon
tRNA carrying a specific amino acid binds to binding site on mRNA via base pairing with its anticodon
Complementary codons and anticodons ensure correct amino acid sequence to form the specific protein primary structure
Ribosome catalyses the formation of peptide bonds between amino acids using energy from ATP
tRNA releases as ribosome moves along mRNA to next codon
Ribosome releases polypeptide into RER when reaches the stop codon
mRNA can associate with another Ribosome to begin translation again
How many ribosomes can translate a molecule of mRNA at oncd
Multiple
Resulting in many polypeptides being formed at once
Or the same mRNA molecule being reused until silenced by RNAi
Explain universal in terms of the genetic code
Same three bases on mRNA/DNA (codon/triplet) code for the same amino acid in all organisms
Same for prokaryotes and eukaryotes
Explain non overlapping in terms of the genetic code
Each base part of only one triplet/codon
During translation each codon is read only once by ribosome
Explain degenerate in terms of genetic code
More than one triplet codes for the same amino acid
Why three bases
There are 20 amino acids
1 base: 4¹ = 4 combinations = 4 amino acids isn’t enough
2 bases: 4² = 16 combinations = 16 amino acids isn’t enough
3 bases: 4³ = 64 combinations = 64 amino acids is enough
Why is the amino acid table in mRNA codons
It is the mRNA that codes for/determines amino acids
What is a mutation
Any change to the DNA base sequence
Occurring randomly and spontaneously
6 types of mutation
Substitution Deletion Addition Translation Inversion Duplication
Explain substitution mutation
One or more bases in a triplet change
Could be a silent mutation in which the amino acid coded for doesn’t change due to the degenerate nature of the genetic code, hence no effect on the polypeptide
If it does alter the amino acid coded for then it will alter the sequence of amino acids In the polypeptide, changing the primary structure
This may change the tertiary structure
Changing the proteins shape and function
Non functional protein
Explain a deletion mutation
A loss of a base in a region of DNA coding for a gene
Alters the triplets from the mutation onwards
Causing a frame shift to the left
If it occurs early in a sequence coding for a gene then likely all triplets will be altered, so all amino acids may change
Lesser effect towards the end since less triplets affected and less alters to amino acid sequence
Can change the primary structure and hence change tertiary structure
May lead to a non functional protein
Explain addition mutation
A gain of a base in a region of DNA coding for a gene
Alters the triplets from the mutation onwards
Causing a frame shift to the right
If it occurs early in a sequence coding for a gene then likely all triplets will be altered, so all amino acids may change
Lesser effect towards the end since less triplets affected and less alters to amino acid sequence
Can change the primary structure and hence change tertiary structure
May lead to a non functional protein
Explain duplication
Duplication of part of a chromosome, the whole chromosome or the whole genome
Explain inversion
Segment of bases is reverses end to end
Explain translocation mutation
When groups of base pairs relocate from one area of the genome to another
Usually between non homologous chromosomes
Essentially an addition or deletion
Explain chromosomal mutations in metaphase 1 of meiosis
During metaphase 1 of meiosis
When homologous chromosomes do not separate after associating
Remaining as a bivalent
Called chromosome non disjunction of homologous chromosomes
Gametes: 2(n+1) 2(n-1)
Explain chromosomal mutations in metaphase 2 of meiosis
During metaphase 2 of meiosis
When sister chromatids do not separate and remain attached via centromere
Called chromosome non disjunction of sister chromatids
Gametes: 2(n) 1(n+1) 1(n-1)
Explain two types of chromosomal mutations
Metaphase 1 and metaphase 2 of meiosis
How can a mutation have a positive result
Change to the DNA base sequence in which a different amino acid sequence coded for
Changing primary structure and therefore tertiary structure
Which is beneficial to the individual
Allows for variation, leading to natural selection and passing on the positive mutation so population is better adapted
Properties of polypeptide change
E.g antibody that makes immune to certain diseases so likely they will survive, thrive and reproduce
E.g enzyme fits substrate better so faster rate of reaction
How can a mutation have no effect
Silent mutation
Base changing has no effect on polypeptide
Since sake amino acid coded for
Due to degenerate nature of genetic code
Mutation occurring in intron
So spliced out in transcription.
May change the primary structure by changing the amino acid sequence
But may not change the tertiary structure if it folds the same due to similar properties of changed amino acid and bonds forming in same place
How can a mutation have a negative effect
Frame shift
All amino acids after mutation change
Give a completely different primary and tertiary structure
Bonds form in different places
So function changes and non functional
If it changes the start/stop codons either no translation or uncontrolled translation
Change of properties of protein (soluble to insoluble)
3 mutagenic agents
High energy ionising radiation
DNA reactive chemicals
Biological agents
Explain high energy ionising radiation
Damage DNA molecule (bases) and chemicals That alter DNA structure Or interfere with DNA replication X rays Gamma Alpha particles Beta particles
Explain DNA reactive chemicals
Can convert DNA bases
Benzene, bromine, hydrogen peroxide
Nitrous acid can remove the NH2 on cytosine and convert it to uracil
Explain DNA reactive chemicals
Can convert DNA bases
Benzene, bromine, hydrogen peroxide
Nitrous acid can remove the NH2 on cytosine and convert it to uracil
Explain DNA reactive chemicals
Can convert DNA bases
Benzene, bromine, hydrogen peroxide
Nitrous acid can remove the NH2 on cytosine and convert it to uracil
Explain biological agents
Viruses and bacteria
Can integrate their genetic code into ours
Occurance of mutations
Spontaneously during DNA replication Natural and random events Causing permebant changes to DNA Which get passed on to generations Occur at a set rate that is different for each species
What are mutagenic agents
Increase the rate of spontaneous mutations
Natural selection
Process by which organisms 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
Over generations
Explain natural selection
Variation due to a mutation
Better adapted individuals more likely to survive and reproduce (differential survival)
These more likely to pass on their advantageous alleles to offspring
Less well adapted fail to survive and reproduce
These less likely to pass on their alleles
Organisms subject to selection pressure in environment
Selection pressure determines the spred of alleles within a gene pool
Can be biotic or abiotic
What is a biotic factor
Living factor
That can act as a selection pressure on a population
Normally have a bigger impact on smaller population
Examples of biotic factors
Predators Prey Diseases Competition Viruses Presence of a mate
What is an abiotic factor
Non living factor
Can act as a selection pressure on a population
Same impact regardless of population size
Examples of abiotic factors
Temperature pH (salinity) Humidity (water potential) Terrain Light intensity Weather
Where does stabilising selection occur
All populations where environment is stable
Stabilising selection
Occurs in all populations where environment is stable
Selection pressure at both ends of the distribution
Favours the average
Those with favoured optimum mean phenotype more likely to survive, thrive, reproduce and pass on advantageous alleles
Differential survival occurs
Those without die out
Over time the mean allele becomes more frequent in the population
Tends to eliminate extremes
Reduces variability (size of range in population)
Reduces opportunity for evolutionary change
Example of stabilising selection
Birth mass
Really heavy/really light babies show higher neonatal mortality rates than medium mass
Over time, selection operates to reduce heavy/light numbers
Directional selection
Environmental change may produce new selection pressure that favours an extremem phenotype
Those with favoured optimum extreme phenotype more likely to survive, thrive, reproduce and pass on advantageous alleles
Differential survival occurs
Those without favoured optimum extreme phenotype die out
Over time the extreme allele becomes more frequent in the population
New mean phenotype that’s shifted along with the normal distribution curve
Example of directional selection
Antibiotic resistance
Speckled moths
Sooty environment meant dark moths more camouflaged so more likely to survive
Explain disruptive selection
Environment has two selection pressures that favour 2 extreme phenotype
Least common but most important for evolution
Those with favoured optimum extreme phenotype more likely to survive, thrive, reproduce and pass on advantageous alleles
Differential survival occurs
Those without favoured optimum extreme phenotype die out
Over time the extreme alleles becomes more frequent in the population
Example of disruptive selection
Mice at beach Light coloured mice blend with sand Dark blend with grass Medium don't camouflage Susceptible to predators
2 types of antibiotic
Narrow spectrum
Broad spectrum
Explain narrow spectrum antibiotics
Antibiotics that act against limited group of bacteria
Explain broad spectrum antibiotics
Antibiotics that zct against a larger group of bacteria
How do antibiotics work
Stop binary fission:
Stop cell wall forming
Stop nucleic acid synthesis
Penicillin/RNA polymerase inhibitor/Cell membrane puncturing
Mechanisms of antibiotic resistance
Plasmids: Contain genes for antibiotic resistance, passed between eachother
Impermeabilty: Modified cell wall that won’t let antibiotic in
Modification: Modified drug target no longer complementary to drug
Pumping it out: Removes drug using ATP
Inactivation: Add a phosphate group to antibiotics to reduce its ability to bind to bacterial ribosomes
Why don’t antibiotics affect human cells
We don’t have cell walls in our cells
Antibiotics prevent cell wall formation
Target bacterial cells replicating by binary fission but human cells don’t replicate by binary fission (mitosis and meiosis)
What is a spectrophotometer
Shines light through bacteria culture
Amount of light that passes through measured
Correlates to amount of bacterial cells (more light passing through means less cells)
Written as a percentage
Issues with spectrophotometer to count cells
Glass tube affects the amount of light passing through
Shouldn’t matter if constant for all readings
Cells sink to the bottom so isn’t accurate
Percentage of light passing through isn’t equal to the number of cells
Total count
Includes living and dead cells
Viable count
Only includes living cells
Turbidity
Cloudiness of a culture
Colony
A cluster of cells
Arise from a single bacterium
By asexual reproduction
What is a serial dilution
Step by step dilutions of a substance to create a range of different concentrations
Can be a method of counting individuals of a large population by obtaining a population density per unit of a culture
Differences between chloroplast DNA and nuclear DNA
Chloroplast is circular/Nuclear is linear
Chloroplast is not associated with histones/Nuclear is associated with histones
Chloroplast is shorter/Nuclear is longer
How do you perform a 1 in 10 serial dilution
Add 9 parts distilled water to 1 part sample solution
Mix
Very important to mix
How do you make a 1 in 100 serial dilution
1 part solution to 99 parts distilled water
Mix
Or
1/10th of a 1 in 10 dilution to 9 parts distilled water
Mix
How do you make a 1 in 1000 serial dilution
1 part sample solution to 999 distilled water
Mix
Or
1/10th of a 1 in 100 dilution to 9 parts distilled water
Mix
Or
1/10th of a 1 in 10 dilution to 99 parts distilled water
Mix
Steps for counting cells via serial dilution
Add x part stock solution to x parts distilled water
Mix
Work aseptically
Sterilise any equipment
Total viable cell count = number of colonies counted × dilution factor
What can splicing produce
Different lengths of mRNA
With different exon arrangements
Function of ribosomes in protein synthesis
Attached to mRNA
Catalyse peptide bonds
Between amino acids of polypeptide chain being synthesised
In translation
Gene pool
Number of different alleles of genes in a population
What is an organisms characteristics determined by
Phenotype
Is determined by the genotype
And it’s interactions with tbe environment
Purine
Adenine
Guanine
Consist of a six-membered and a five-membered nitrogen-containing ring fused together
Pyrimidine
Thymine
Cytosine
Uracil
Consist of only a six-membered nitrogen-containing ring
