Protein Synthesis & Selection Flashcards
What does a nucleotide consist of?
a deoxyribose, a phosphate group and a nitrogenous base
What does a double helix consist of?
two polynucleotide strands
How are nucleotides made?
by joining adjacent DNA nucleotides by phosphodiester bonds (through condensation reactions, catalysed by DNA Polymerase)
What are 2 polynucleotide strands held together by?
hydrogen bonds between complimentary base pairs (Adenine to Thymine and Cytosine to Guanine)
What does a double helix consist of?
2 polynucleotide strands
What is each nucleotide formed from?
a deoxyribose, a phosphate group and a nitrogenous base
How are 2 polynucleotides made?
by joining adjacent nucleotides by phosphodiester bonds (through condensation reactions, catalysed by DNA Polymerase)
How are polynucleotide strands held together?
by hydrogen bonds between complimentqry bqse pairs (Adenine to Thymine and Cytosine to Guanine)
What is the difference between eukaryotic and prokaryotic cells?
-eukaryotic cells are cells with a true nucleus
-prokaryotic cells are cells without a nucleus
Give some examples of eukaryotic cells
all cells that are in animals, plants and fungi
Give some examples of prokaryotic cells
archaeal and bacteria cells
Describe Eukaryote’s DNA
-1 strand contains genes (base pairs)
-within this is an exon
-this will also be an intron
-to get into cells, it wraps around histone proteins
-linear
Describe Prokaryote’s DNA
-contains mitochondria and chloroplasts
-no ends (circular)
-much shorter than eukaryotic DNA (SO doesnt need support from histone proteins)
-no means no (nucleus)
Contrast eukaryotic and prokaryotic DNA (3)
-eukaryotic is linear WHEREAS prokaryotic is circular
-eukaryotic is associated with histone proteins WHEREAS prokaryotic is not associated with histone proteins
-eukaryotic contains introns WHEREAS prokaryotic does not contain DNA
What is an intron?
non coding sequence within a gene of DNA (interrupt but don’t do anything)
What is an exon?
a coding sequence within a gene of DNA
What are the 4 types of RNA?
-messenger RNA (mRNA)
-transfer RNA (tRNA)
-Ribosomal RNA (rRNA)
-interfering RNA (RNAi)
What is the role of mRNA?
formed during transcription
What is the role of tRNA?
involved in translation
What is the role of rRNA?
consists of a large and a small subunit, site of translation
What is the role of RNAi?
inhibits translation
Describe mRNA (6)
-this is a single stranded polynucleotide chain
-it is a complimentary copy of a single gene from the TEMPLATE strand of DNA
-a gene is a sequence of nucleotides that codes for a primary structure of a polypeptide chain
-mRNA’s length varies depending on the number of bases that make up the gene (so its much shorter than DNA)
-the sequence of bases on the mRNA are complimentary to the sequence of bases of the gene it is copying
-complimentary base pair rules: A-U and C-G
What us the rule of copying a DNA template strand onto the mRNA strand?
-pairs with the opposite base
-Uracil is in mRNA ONLY
Contrast DNA and mRNA (6)
-DNA is double stranded WHEREAS RNA is single stranded
-DNA is longer WHEREAS RNA is shortER
-Thymine in DNA WHEREAS it is replaced with Uracil in RNA
-Deoxyribose in DNA WHEREAS Ribose in RNA
-DNA has hydrogen bonds WHEREAS mRNA doesn’t have hydrogen bonds
-DNA has introns whereas mRNA doesn’t have introns
Describe the similarities between DNA and mRNA (2)
-both are polymers of nucleotides
-both made from nucleotides linked by phosphodiester bonds
Describe the structure of tRNA (5)
-consists of one polynucleotide chain of about 75 nucleotides
-has regions where the strand is folded over but it is single stranded
-it has a cloverleaf structure held by hydrogen bonds
-has an amino acid attatchment site where only a specific amino acid binds
-has a region of 3 bases known as an anticodon
What is the role of a tRNA molecule?
-to carry a specific amino acid to the ribosome (site of protein synthesis)
What is the difference between a DNA triplet, a mRNA codon and a tRNA anticodon?
DNA triplet- consists of normal base pairs (A, T, C and G) e.g ACT
mRNA codon is opposite and has Uracil (UGA)
tRNA anticodon also has uracil and is the opposite of the mRNA/codon (ACU)
Define the term genome
complete set of genes in a cell
Define the term proteome
full range of proteins that a cell is able to produce
Define the term Loci
position of a gene within chromosomes
Define the term Allele
a different version/ form of a gene
Define the term Gene
a DNA base sequence that codes for a sequence of amino acids in a polypeptide
What two processes are involved in protein synthesis?
-transcription
-translation
What does transcription involve?
-making a copy the base sequence of a specific gene (DNA) onto the base sequence of a mRNA molecule
What does translation involve?
-the conversion of a base sequence of mRNA (at a ribosome) into the specific amino acid of a polypeptide chain (primary structure of a polypeptide)
Where does transcription occur in prokaryotes?
in the cytoplasm
(because there is no nucleus). they also dont have introns so no splicing
Where does transcription occur in eukaryotes?
in the nucleus
What is the molecule formed during transcription?
pre-mRNA
How is mature mRNA formed?
-pre-mRNA is spliced (introns removed and the exons are rejoined) to form the mature mRNA
-prokaryotes are unable to splice pre-mRNA
What are the key processes in transcription?
- forming a pre-mRNA molecule from the DMA
- removing introns to create a mature mRNA molecule
How is a pre-mRNA molecule formed during transcription? (7)
-DNA Helicase unwinds double DNA double helix at site to be transcribed
-Hydrogen bonds between the strands are broken and so the strands separate
-only 1 strand acts as a template
-complimentary free RNA nucleotides associated with exposed DNA bases via complimentary base pair rules on the template strand only
-Uracil to Adenine and Cytosine to Guanine
-RNA Polymerase joins adjacent RNA nucleotides together (condensation reaction forming phosphodiester bonds)
-mRNA formed is complimentary to DNA and is called pre-mRNA (contains introns and exons)
How are introns removed to create a mature mRNA molecule during transcription? (3)
-introns are now removed by splicing to produce mature mRNA
-exons are spliced back together to produce a mRNA molecule that only has coding regions from the gene
-mRNA passes out of the nucleus via nuclear pore to the RIBOSOME (site of protein synthesis)
Where does translation occur?
In the cytoplasm at a ribosome
What are ribosomes made from?
rRNA and ribosomal proteins
What happens to mature mRNA during translation?
It leaves the nucleus through pores in the nuclear membrane and passes into the cytoplasm
Describe translation (7)
-mRNA binds to the ribosome
-ribosome finds the START codon
-two codons/binding sites
-tRNA with complimentary anticodons binds to the codon
-catalyses the formation of peptide bonds between amino acids (held by tRNA molecules) using energy from ATP
-tRNA is released as ribosome moves along (mRNA to the next codon)
-ribosome releases polypeptide into RER when the STOP codon is reaches
What does protein synthesis require?
The energy from the hydrolysis of ATP into ADP and Pi
What happens when many ribosomes can translate a molecule of mRNA at the same time?
-many polynucleotides are synthesised are at once or the same mRNA molecule can be used in translation multiple times, until the mRNA is silenced by RNAi
Describe the detailed process of translation (15 points)
-mRNA binds to a ribosome
-tRNA carrying a specific amino acid occupies the first binding site where the START codon on the mRNA is located, via base pairing with tRNA anticodon
-ATP is required to activate each tRNA
-a second tRNA carrying a specific amino acid binds to the second tRNA binding site on mRNA, via base pairing with its anticodon
-complimentary codon & anticodons ensure the correct sequence of amino acids to form the specific proteins PRIMARY STRUCTURE
-Ribosome catalyses the formation of peptide bonds between the amino acids through condensation
-ribosome moves along mRNA to include the next codon (translocation)
-the tRNA is lost from first codon it no longer has an amino acid
-a third tRNA carrying a specific amino acid binds to the third codon in the mRNA via base pairing with its anticodon
-ribosome catalyses the formation of peptide bonds between the amino acids through condensation
-Ribsome moves along mRNA to include the next codon
-this process repeated, with the addition of one amino acid each time until the stop codon is reached
-the polypeptide is then released into the RER as the ribosomal complex falls apart
-the polypeptide is now transported to the GOLGI body for modification before being packaged into Golgi vesicles for secretion
-the mRNA can associate with another ribosome to begin translation again
What are the terms for the bases in DNA, mRNA and tRNA?
DNA- triplet
mRNA-codon
tRNA-anticodon
What does it mean that the genetic code is universal? (1)
The same 3 bases on mRNA code for the same amino acid in all organisms
What does it mean that the genetic code is non overlapping?
Each base is read once in a triplet
What does a degenerate code mean?
More than one triplet (DNA) codes for an amino acid
What is a STOP codon?
A codon that keeps going until something makes it stop
How many amino acids and how many combinations of triplets are there?
20 amino acids
64 combinations of triplets/codons
What is a mutation?
Any change to the DNA base sequence
What are the 3 types of mutations?
Substitution mutations
Addition/ deletion mutations
Chromosomal mutations
What may mutations be caused by?
Radiation, chemicals, copying DNA or heavy metal ions
What may mutations be caused by?
Radiation or chemicals
Where do mutations occur?
Can occur anywhere in a base (1st, 2nd or 3rd)
What is the effect of a mutation?
Can be positive, negative or have no effect
What can a mutation in DNA lead to?
A change in the primary structure of polypeptides, sequence of amino acids in the polypeptide chain (different protein may be produced) but might not because the code is degenerate
What may be the consequences of a mutation in the primary structure in a DNA sequence
-May alter the secondary structure ( change the position of weak H bonds affecting the alpha helices and B pleated sheets)
-May alter the tertiary structure (changes the position of weak H bonds, ionic bonds and the disulphide bonds)
What is a substitution mutation in the third base?
-A Substitution in the third base would not alter the amino acid
-this is known as a silky mutation whereby the mutation does not change the amino acid coded for, so it will have no effect on the polypeptide chain
What is a substitution mutation in the first base?
It alters the amino acid sequence, which will alter the sequence of amino acids on the polypeptide chain, so it may alter its specific tertiary structure (can cause a non functional protein)
What happens when a mutation causes a triplet to code for a STOP codon?
It will cause the growing polypeptide chain to terminate prematurely (instead of the amino acid, this will stop the polypeptide chain) and may not be able to perform its intended function (depending on how early the termination occurred)
What is an addition/deletion mutation?
-1 full DNA nucleotide is gained or lost within a gene
-this results in an alteration of the base triplets from the mutation onwards
What is a frame shift?
When the reading frame in an addition/ deletion mutation has been shifted to the right/left by one base
(Bases have been moved and the sets of 3 bases are read differently )
Would an addition/deletion mutation have a greater effect if it was at the start or the end of the polypeptide chain?
-the earlier it occurs, the more polypeptides could be affected, so more amino acids would be altered.
-towards the end it would have a lesser effect but would still alter some amino acids at the end of a gene
What is a wild type gene?
The original gene you have without any mutations
What happens if we have a different reading frame (the frame shifts) ?
-different sequence of triplets in DNA
-different primary structure of polypeptide
-different positions of R groups
-different tertiary structures
When do mutations occur?
They occur spontaneously and are natural and random events that cause permanent changes to the DNA base sequence which is passed onto future generations that occur at a set rate
What can mutagenic agents/mutations be?
-advantageous
-disadvantageous
-neutral
What do mutations often produce?
-organisms that are less well adapted to their environment and can alter cellular activities
-mutations in gametes often proves fatal
What do mutagenic agents do and include?
-they increase the rate of spontaneous mutation
they include:
- high energising radiation
-DNA reactive chemicals
-biological agents such as viruses and bacteria
What is a chromosomal mutation?
-within meiosis cells divide so daughter cells contain one of each homologous chromosome
-sometimes this goes wrong and daughter cells are produced containing too many chromosomes
-a pair of chromosomes may fail to aperste which is called chromosome non-disjunction
-this causes down syndrome
What is an inversion mutation?
When a segment of bases is reversed end to end
What is a duplication mutation?
A doubling of part of a chromosome, of an entire chromosome, or even the whole genome
What is a translocation mutation?
-when groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes
What is selection?
A process that results in the best adapted individuals in a population, surviving to breed and so pass their favourable alleles to the next generation
What is a phenotype?
An organisms characteristics
What is a genotype?
All the alleles an organism has
What is an allele?
A different version of the same gene
What is an organisms phenotype determined by?
It’s genotype and its interactions with the environment
What is a gene pool (genetic diversity) ?
The number of different alleles of genes in a population
What can mutations introduce to populations and how can they do this?
-can introduce new alleles
- the only way to make a new allele is through mutation.
-‘new combinations’ 9; alleles can be made through meiosis & sexual reporoduction
What is natural selection?
-a process by which organisms that are better adapted to the environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population (passed onto the next generation)
Why might natural solution occur?
-predation, disease and competition for the means of survival result in differential survival and reproductive successes
Describe the process of natural selection
-variation exists within a population (caused by a mutation)
-better adapted individuals more likely to survive and reproduce (differential reproductive success)
-these organisms are more likely to pass on their alleles
-those which are less well adapted fail to survive and reproduce
-these organisms are less likely to pass on their alleles
-organisms are therefore subject to selection pressure due to the environment they live in
What is selection pressure and what does it determine?
-it discrete a advantageous/ deleterious alleles and controls the spread and frequency of alleles within a gene pool
-it determines the spread of an allele within the gene pool
-selection pressures are either BIOTIC or ABIOTIC
What are some biotic factors to natural selection?
-number of predators
-number of prey
-pathogens (bacterial)
-lack of food availability
-presence of a mate
What are some abiotic factors to natural selection?
-PH of soil
-humidity
-light intensity
-temperature
-salinity (how salty water is)
What are biotic and abiotic factors and how much of an effect do they have?
-biotic is living factors
-these have a bigger impact on a big population
-abiotic are non living factors
-these have the same impact on a small or large population
What are the different types of selection?
-directional, stabilising and disruptive
What are the types of adaptations and give examples
-anatomical (how they look)-Arctic foxes have thicker fur than warmer climate foxes
-physiological (how their body works)-kangaroos oxidise fats instead of carbs for extra water
-behavioural (how they behave)- swallows migrate in autumn for better weather
Compare and contrast trNA and mRNA (5)
-mRNA doesn’t have hydrogen bonds but tRNA does
-mRNA is linear by tRNA has a clover leaf structure
-both are single stranded
-both are made from nucleotides
-forming phosphodiester bonds
What 4 things does a tRNA molecule contain?
-sugar phosphate backbone
-amino acid binding/attachment site
-hydrogen bonds between complimentary base pairs
-anticodons
Describe stabilising selection
-selection agains both extremes, (occurs when the environment is stable and favours the average, it reduces variability)
-only mean phenotype will have reproductive success
-alleles for mean phenotype are passed onto future generations in greater numbers
-over time the frequency of mean alleles coding for the mean phenotype increases
-alleles coding for both extremes phenotypes decrease
Draw a graph for stabilising selection
Draw a graph for stabilising selection
Give an example of stabilising selection
-birth weight in humans
(-selection agains birth extremes -high and low birthweights)
(-Mean phenotype of medium birthweight will be more likely to survive and reproduce)
(-alleles for medium birthweight are passed onto future generations )
(Overtime, frequency of the allele coding for medium birthweight increases)
(Alleles for both extremes- high and low birthweights decrease)
What are selection pressures and what can they do?
- determine the spread of an allele within a gene pool
-They can be biotic or abiotic
-They can dictate advantageous/deleterious alleles
Describe directional selection
-Selection for only one extreme
-Individuals with advantageous alleles have increased reproductive success
-Alleles for one extreme are passed onto future generations in greater numbers
-overtime, frequency of this extreme allele coding for extreme phenotype increases
-alleles coding for the other extreme phenotype decreases within the population
Give an example of directional selection
-antibiotic resistance in bacteria
(-variation due to mutation to create new advantageous alleles that give antibiotic resistance
-Selection for advantageous phenotype of antibiotic resistance and against non-resistant bacteria if antibiotics are taken
-Antibiotic resistant bacteria are more likely to survive and reproduce
-Alleles for antibiotic resistance is passed on to future generation
-Overtime, the frequency of the allele coding for antibiotic resistance increases
-increase in antibiotic resistant bacteria in the population)
Draw a graph for directional selection
Draw a graph for directional selection
What is the only way you can make a new allele?
through mutation (new combinations of alleles are made through meiosis and sexual reproduction)
What can mutations provide?
-Selective advantage
-Neutral
-Selective disadvantage
Explain how selection occurs in living organisms (6)
-(named example) variation due to mutation
-Different environmental/abiotic/biotic conditions/selection pressures
-Selection for different/advantageous features/characteristics/mutations/alleles
-Differential reproductive success/organism survive and reproduce
-leads to change in allelic frequency
-Occur over a long period of time
What is evolution by natural selection?
A change in the allelic frequency within a population
What was you always state about the population in terms of selection?
That the allelic frequency increases/decrease
How can you count bacteria?
Through serial dilution
How do you conduct serial dilutions?
-A culture medium holds millions of bacteria
-By taking one part of this culture, medium and mixing nine parts sterile water you complete a 1/10 dilution
-This divides the number of bacteria in the culture medium by 10
-You can continue this process to create a serial dilution
-By taking one ML of the previous resolution and adding it to 9ML of sterile water (this creates a 1/100)
What is the equation for the number of bacteria in the original culture medium?
Number of colonies x dilution factor
Work out the number of bacteria colonies if there is 17 colonies and a 1/1000 dilution factor
-do the number of colonies x dilution factor
-17 x 10,000= 170,000
-The original culture medium contains 1,700,000 bacteria colonies
What will happen if you use a serial dilution which is too low to cut the number of bacteria?
-The count is unlikely to be reproducible and accurate
- As there are too many cells so they will be overlapping
What will happen if you use the serial dilution which is too high to count the number of bacteria?
It will lead to the original dilution being so diluted that there will be ?? remaining bacteria present to see
How can you calculate the number of bacteria on a logarithmic scale?
Log x (y)
x = number of divisions
y= number of bacteria
Explain how a gene codes for a protein (2)
-Basic sequence on DNA determines the sequence of amino acids
-Homologous chromosomes are pairs of chromosomes within the same genes
