D1.2 Protein synthesis Flashcards
What unique properties does a protein rely on
which amino acids are used in its construction
the sequence of the amino acids
What catalyses the formation of mRNA
RNA polymerase and the mRNA is formed through the process transcription
what is mRNA
a complementary copy of the genetic code of a gene
what happens to the template strand in transcription
becomes the template for transcription and a single stranded molecule of RNA is formed by complementary base pairing
what happens to the mRNA after transcription
travels into the cytoplasm and passes to ribosomes for synthesis of proteins
in transcription, why are hydrogen bonds between strands broken
allows the double helix of a particular gene to be unwinded
what happens to cells that do not divide during the lifetime of the organism (somatic cells)
their base sequences must be conserved throughout the life of the organism to ensure the ongoing functioning of the cells through transcription and translation
what is transcription in terms of gene expression
the first stage of gene expression where gene can be switched on or off. Organisms can control which gene is expressed
also related to when and where proteins are coded for
where is gene expression completed
in the process of translation at ribosomes where sequence of bases within DNA is expressed to form proteins
what is Transfer RNA responsible for
translating a three base sequence into an amino acid sequence
what is the shape of tRNA
clover leaf shape
there are different tRNAs for each of the 20 amino acids
What is the features of the tRNA
at the end is a site where one particular amino acid can be bonded covalently
At the other end, there is a sequence of three bases called an anticodon, which is complementary to the codon of mRNA that codes for the specific amino acid
how does the amino acid become attached to the tRNA
by an enzyme that requires ATP. they are specific to particular amino acids which is a way of making sure the correct amino acids are used in the sequence
where does mRNA bind to the ribosome
during translation, mRNA binds to the small subunit of the ribosome so two tRNAs can bind simultaneously to the large subunit
how does a ribosome move along the mRNA
moves along reading the codons ( moves in steps of 3)from the start codon
The sequence of the three bases in the codons is complementary to the sequence of bases in the anticodon
what happens in the ribosome, mRNA, tRNA during translation
for each mRNA codon, the complementary anticodon of the tRNA-amino acid complex slots into place and held by hydrogen bonds
the amino acids of the neighbouring tRNA- amino acid complex are joined by peptide linkages which frees the first tRNA
process continues until stop codon is reached
how does similarity of codons and amino acids support idea of common origin of life
process of reading code and protein synthesis is very similar in prokaryotes and eukaryotes.
Referred to as universality of the genetic code
what is degeneracy of the genetic code
most amino acids are coded by more than one codon
degenerate code provides enough different to code for all amino acids and possibility of mutation
due to degeneracy, what is the likely outcome of a mutation in a single base of a codon
likely it does not change the info required for the protein very much, so there is not much of an effect
a codon size of three gives how many combinations of amino acids
64 combinations which has the ability to also cope with any expansion in the number of amino acids during evolution
what is mutation
when there are changes to the sequence of nucleotides in DNA
what is a point mutation
occurs when a single base pair is added, deleted or changed within a molecule
what can happen when an amino acid in the sequence of a protein is changed
the properties of the protein can be altered drastically
what is a common example of a point mutation
sickle cell anaemia
what happens in sickle cell anaemia
base A becomes T which leads to hydrophobic spot in a hydrophilic section of the protein
haemoglobin molecules can the clump together, distorting RBC into sickle chapes, and cannot transport oxygen or move, preventing blood circulation
what do people with sickle cells suffer from
anaemia due to lack of transport of oxygen
some can be mildly anaemic
if someone has both alleles for sickle cell, they can have serious heart and kidney problems
What does RNA polymerase require to start synthesis of a new RNA strand
requires a free 3’ OH group
in what direction are the codons of mRNA read during translation
read from the 5’ end to the 3’ end by tRNAs
what happens before mRNA can be transcribed by the enzyme RNA polymerase
it binds with a small group of proteins known as general transcription factors at a sequence of bases known as the promoter
only when the complex has been formed, can transcription be started
Where to promoter regions occur
on DNA strands before the start of a genes sequence of bases
What does RNA polymerase do once transcription has been initiated?
moves along the DNA untwisting the helix as it goes and exposing the nucleotides, allowing RNA nucleotides to pair, forming a mRNA strand
how can rate of transcription be increased/decreased
by binding of specific transcription factors on the enhancer site for the gene
Much of DNA is not used for protein synthesis, or regulation of genes. What do these non gene regions consist of
introns
telomeres
genes for tRNA
major lengths of non coding DNA
what are introns
non coding nucleotide sequences, which can also interrupts the exons of genes
what are telomeres
special nucleotide sequence, usually repetition of a short nucleotide sequence
seal the ends of DNA and stop erosion of genes
what are genes for tRNA in the non gene regions of chromosomes
code for relatively short lengths of RNA that are formed in the nucleus and pass out into the cytoplasm
amino acids are transported to supply a growing polypeptide in the ribosome
what are the major lengths of non coding DNA
when short sequence of bases are repeated many times, they often occur in clusters, known as Variable Number tandem repeats
How do telomeres stop erosion of genes
protect chromosomal ends by binding proteins to form telomere caps
stop the end of chromosomes attaching to each other, avoiding cell death
recognition sites for the enzyme telomerase enables telomeres to lengthen
what are exons
sections of genes that carry meaningful info
how are introns removed from the mRNA in post transcriptional modification
introns spliced out using spliceosomes
spliceosomes recognise highly conserved regions between the 3’ end of the exon and the 5’ end of the intron, then cleave phosphodiester bond between the nucleotides
exons then joined together to form one polypeptide from the gene
what is the process of removing introns known as
splicing
what is alternative splicing
they can join together different combination of exons to form different types of polypeptides from a single gene
how is the process of post transcriptional modification completed
ends of the mRNA are modified to increase the stability of the molecule
what is polyadenylation
poly A polymerase adds a chain of adenine nucleotides known as a poly A tail to mRNA molecule.
3’ end of the pre mRNA is cleaved to a free hydroxyl group
how is the 5’ end capped off in post transcriptional modification
capped off by addition of 5’ modified guanine nucleotide
what is the result of capping off both ends in post transcriptional modification
mature mRNA is formed that will be protected from enzymatic degradation in the cytoplasm
means a single gene can code for more than one type of polypeptide
what are isoforms
two different types of proteins
due to alternative splicing what is a possible result
number of proteins produced can be greater than the number of genes present
how are amino acids activated for protein synthesis
combination with a short length of tRNA through an activation process involving ATP
how many different tRNA molecules are there
20, one for each amino acid
how do different tRNA molecules differ
they all have clover leaf shape, but they differ in the sequence of bases, known as anticodons which is exposed on one of the clover leaves
where is each of the amino acids attached to the tRNA molecule
attached to the 3’ terminal of its specific tRNA molecule by a tRNA activating enzyme
what are the steps of amino acid activation
specific amino acid and a molecule of ATP binds to a tRNA activating enzyme, amino acid activated by hydrolysis of ATP and the bonding of AMP, two phosphate groups linked together are released
tRNA specific to the amino acid binds to the active site of the enzyme
amino acid binds to the attachment site on the tRNA, and then the AMP is released
the activated tRNA with attached amino acid is released from the enzyme
what is the structure of the ribosome
consists of a large and a small subunit, both composed of RNA and a protein
what are the three sites in the ribosome where tRNAs interact
A site ( first)
P site ( second)
E site ( third)
what is the function A site in the ribosome
a codon of the incoming mRNA binds to a specifc tRNA-amino acid through its anticodon ( complementary base pairing)
function of the P site in the ribosome
amino acid attached to its tRNA is condensed with the growing polypeptide chain by formation of a peptide linkage
function of the E site in the ribosome
tRNA leaves the ribosome, following transfer of its amino acid to the growing protein chain
how is translation initiated
translation begins when an mRNA molecule binds with the small ribosomal subunit at the 5’ end of the mRNA. joined by the initiator tRNA. followed by attachment of a large ribosomal unit. Initiator tRNA occupies the P site in the assembled ribosome
the next codon of the tRNA present in the A site, is available to a tRNA with the appropriate anticodon
two activated amino acids are put into position and a peptide bond forms between them by a condensation reaction
reaction is catalysed by enzymes present in large subunit
process of elongating the peptide in translation
ribosome moves three bases along the mRNA
tRNA in P site moves to the E site and is released, bringing the next codon to occupy the A site, allowing a tRNA with the appropriate anticodon to bind to that codon, bringing other amino acids
while a.a held together, peptide bond is formed
polypeptide is formed and emerges from large subunit
how is translation terminated
a stop codon is reached, the completed polypeptide is released from the ribosome
what is post translational modification
many polypeptides must be modified before they can function
what is an example of post translational modification
insulin
goes from pre-pro insulin to pro insulin and then to insulin
what is done to maintain the proteome
proteins are continually synthesized by translation and broken down by hydrolysis reactions
what is the result of proteome being maintained
constant turnover of proteins, ensures maintenance of optimally functioning proteins
what are proteasomes
the carry out breakdown of proteins
they degrade proteins that are damaged, misfolded or no longer needed
how are proteins marked for degradation
by attachment of regulatory proteins known as ubiquitin, binds to proteasome which feeds the protein into the core particle where it is broken down into peptides
peptides are further processed to provide amino acids for new proteins
