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BIO HL > D1.2 Protein synthesis > Flashcards

D1.2 Protein synthesis Flashcards

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1
Q

What unique properties does a protein rely on

A

which amino acids are used in its construction
the sequence of the amino acids

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2
Q

What catalyses the formation of mRNA

A

RNA polymerase and the mRNA is formed through the process transcription

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3
Q

what is mRNA

A

a complementary copy of the genetic code of a gene

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4
Q

what happens to the template strand in transcription

A

becomes the template for transcription and a single stranded molecule of RNA is formed by complementary base pairing

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5
Q

what happens to the mRNA after transcription

A

travels into the cytoplasm and passes to ribosomes for synthesis of proteins

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6
Q

in transcription, why are hydrogen bonds between strands broken

A

allows the double helix of a particular gene to be unwinded

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7
Q

what happens to cells that do not divide during the lifetime of the organism (somatic cells)

A

their base sequences must be conserved throughout the life of the organism to ensure the ongoing functioning of the cells through transcription and translation

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8
Q

what is transcription in terms of gene expression

A

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

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9
Q

where is gene expression completed

A

in the process of translation at ribosomes where sequence of bases within DNA is expressed to form proteins

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10
Q

what is Transfer RNA responsible for

A

translating a three base sequence into an amino acid sequence

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11
Q

what is the shape of tRNA

A

clover leaf shape
there are different tRNAs for each of the 20 amino acids

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12
Q

What is the features of the tRNA

A

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

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13
Q

how does the amino acid become attached to the tRNA

A

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

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14
Q

where does mRNA bind to the ribosome

A

during translation, mRNA binds to the small subunit of the ribosome so two tRNAs can bind simultaneously to the large subunit

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15
Q

how does a ribosome move along the mRNA

A

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

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16
Q

what happens in the ribosome, mRNA, tRNA during translation

A

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

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17
Q

how does similarity of codons and amino acids support idea of common origin of life

A

process of reading code and protein synthesis is very similar in prokaryotes and eukaryotes.
Referred to as universality of the genetic code

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18
Q

what is degeneracy of the genetic code

A

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

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19
Q

due to degeneracy, what is the likely outcome of a mutation in a single base of a codon

A

likely it does not change the info required for the protein very much, so there is not much of an effect

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20
Q

a codon size of three gives how many combinations of amino acids

A

64 combinations which has the ability to also cope with any expansion in the number of amino acids during evolution

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21
Q

what is mutation

A

when there are changes to the sequence of nucleotides in DNA

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22
Q

what is a point mutation

A

occurs when a single base pair is added, deleted or changed within a molecule

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23
Q

what can happen when an amino acid in the sequence of a protein is changed

A

the properties of the protein can be altered drastically

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24
Q

what is a common example of a point mutation

A

sickle cell anaemia

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25
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
26
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
27
What does RNA polymerase require to start synthesis of a new RNA strand
requires a free 3' OH group
28
in what direction are the codons of mRNA read during translation
read from the 5' end to the 3' end by tRNAs
29
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
30
Where to promoter regions occur
on DNA strands before the start of a genes sequence of bases
31
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
32
how can rate of transcription be increased/decreased
by binding of specific transcription factors on the enhancer site for the gene
33
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
34
what are introns
non coding nucleotide sequences, which can also interrupts the exons of genes
35
what are telomeres
special nucleotide sequence, usually repetition of a short nucleotide sequence seal the ends of DNA and stop erosion of genes
36
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
37
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
38
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
39
what are exons
sections of genes that carry meaningful info
40
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
41
what is the process of removing introns known as
splicing
42
what is alternative splicing
they can join together different combination of exons to form different types of polypeptides from a single gene
43
how is the process of post transcriptional modification completed
ends of the mRNA are modified to increase the stability of the molecule
44
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
45
how is the 5' end capped off in post transcriptional modification
capped off by addition of 5' modified guanine nucleotide
46
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
47
what are isoforms
two different types of proteins
48
due to alternative splicing what is a possible result
number of proteins produced can be greater than the number of genes present
49
how are amino acids activated for protein synthesis
combination with a short length of tRNA through an activation process involving ATP
50
how many different tRNA molecules are there
20, one for each amino acid
51
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
52
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
53
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
54
what is the structure of the ribosome
consists of a large and a small subunit, both composed of RNA and a protein
55
what are the three sites in the ribosome where tRNAs interact
A site ( first) P site ( second) E site ( third)
56
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)
57
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
58
function of the E site in the ribosome
tRNA leaves the ribosome, following transfer of its amino acid to the growing protein chain
59
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
60
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
61
how is translation terminated
a stop codon is reached, the completed polypeptide is released from the ribosome
62
what is post translational modification
many polypeptides must be modified before they can function
63
what is an example of post translational modification
insulin goes from pre-pro insulin to pro insulin and then to insulin
64
what is done to maintain the proteome
proteins are continually synthesized by translation and broken down by hydrolysis reactions
65
what is the result of proteome being maintained
constant turnover of proteins, ensures maintenance of optimally functioning proteins
66
what are proteasomes
the carry out breakdown of proteins they degrade proteins that are damaged, misfolded or no longer needed
67
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

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