Protein Synthesis🥩 Flashcards
(69 cards)
1
Q
What is genetic code?
A
The information required to determine all the characteristics of an organism
2
Q
What is a protein?
A
A large polypeptide consisting of 1 or more polypeptide chains, made up of 100s of amino acids
3
Q
What is a polypeptide?
A
A polymer consisting of a chain of amino acid monomers joined by peptide bonds
4
Q
What is a gene?
A
A length of DNA that codes for a polypeptide or a length of RNA that is involved in regulating gene expression
5
Q
What is a genome?
A
The entire DNA sequence of an organism
6
Q
What is a locus?
A
A specific position on a chromosome occupied by a specific gene
7
Q
How many amino acids are there?
A
20
8
Q
How many combinations of codons does a triplet code provide?
A
64 (4^3)
9
Q
What is the triplet code?
A
- A three base code
- As there are only 20 amino acids, each amino acid has more than one codon that codes for it
- 3 DNA bases code for one amino acid
- Non-overlapping
10
Q
What did the frame shift experiments show?
A
- Using enzymes, they added or deleted nucleotide bases in the DNA of a viruses that infects bacteria
- They found that when 1 or 2 bases were added/deleted, the viruses were unable to infect the bacteria
- But when 3 bases were added/deleted, the virus was able to infect the bacteria
- Concluded that’s adding/removing 1 or 2 bases caused a ‘frame shift’ which inactivated the gene
- However, adding or removing 3 bases only partially affected the gene
- The results also showed that the code is non-overlapping
11
Q
What does non-overlapping mean?
A
•Each triplet DNA specifies one amino acid
•Each base is part of only one triplet, so is involved in specifying only one amino acid
•Requires a longer sequence of bases than overlapping code
-however, changing one base has small or no effect
12
Q
What does overlapping mean?
A
- A much shorter length of DNA would code for a polypeptide
* If one central base was changed, all three codons in the mRNA would be different
13
Q
What are mutagens?
A
- Factors that increase mutation rate
- E.g. ionising radiation - gamma, UV, x-rays
- E.g. chemicals - polycyclic hydrocarbons
- E.g. carcinogens - mutagens that lead to cancer
14
Q
What are proto-oncogenes?
A
- Can mutate to become oncogenes
* Can lead to uncontrolled cell division - tumour
15
Q
What is a codon?
A
- The three bases that code for an amino acid
* Form a unit of genetic code in a DNA or RNA molecule
16
Q
What’s the advantage of having more than one codon for many amino acids?
A
If there is a mutation and a base changes, the same amino acid may still be produced
17
Q
What does degenerate mean?
A
When there are many triplets that code for the same amino acids
- means mutations aren’t always significant
18
Q
What are the three types of mutations?
A
- Substitution
- Deletion
- Insertion
19
Q
Why is substitution not always serious?
A
Degenerate code means the amino acid in the polypeptide may not be changed
-3D structure may not change, so function of protein may not change
20
Q
What is a mutation?
A
- Spontaneous, random events that change genetic material
* May not affect phenotype
21
Q
What are the main features of the genetic code?
A
- Triplet code
- Linear code
- Degenerate code
- Punctuation codons
- Almost universal
22
Q
Explain the triplet code
A
- Each of the 20 a.acids is represented by a three letter abbreviation
- Base triplet in DNA
- Codon in mRNA
23
Q
Explain the linear code
A
- Reads from a starting point to a finishing point
* Codon is always read from 5’ -> 3’
24
Q
Explain the degenerate code
A
- More codons than amino acids
* Most amino acids are coded for by more than one codon
25
Explain punctuation codons
* Start and end of a coding sequence in a cistron is determined by specific codons
* Start
* Stop
26
What is the start codon?
* AUG
| * Code for methionine
27
What are the stop codons?
* UAA
* UAG
* UGA
28
Explain the idea of the genetic code being almost universal
* Most organisms share the same code
* Chloroplast and mitochondria DNA have a slightly modified code
* Other exceptions to the universal genetic code are rare
29
What are cistrons?
Sections of DNA which contain info needed to make a particular polypeptide
30
What is the start codon?
Methionine
Met
AUG
31
What are the three stop codons?
UAA
UAG
UGA
32
What is the codon for glutamine?
Gln
| CAG and CAA
33
What are the codons for Alanine?
Ala
| GCU, GCC, GCA, GCG
34
What is the one gene - one polypeptide hypothesis?
* Proteins can consist of more than one polypeptide chain, each determined by the action of a different gene
* A gene is a specific sequence of DNA bases that codes for a specific polypeptide
* BEEN DISPROVED
35
Why is the one gene - one polypeptide hypothesis wrong?
* Some proteins are made of more than one polypeptide chains
| * More than one gene may be needed to produce the protein
36
What is an intron?
* A sequence of nucleotides that lies between the cistrons that code for polypeptides
* ’Intrude’ into the cistron
* Not expressed in the final protein
37
What is an exon?
* The regions of the DNA that contain the code for proteins
* Remaining sections after the introns have been cut out and removed from the pre-mRNA
* ‘Expressed’
38
What is an antisense strand?
Transcribing/coding strand
39
What is a sense strand?
Non-transcribing strand
40
What is mRNA?
* Messenger RNA
* Carries genetic information to ribosomes in the cytoplasm, where it is used to make the polypeptides that make up a protein
* 3 bases makes a codon
41
What is tRNA?
* Transfer RNA
* Transports amino acids to the ribosomes during protein synthesis
* About 20 groups, each specific for one kind of a.acid and consists of a single polynucleotide strand of RNA, about 80 bases long
* Strand is folded to form a clover-leaf arrangement held in place by hydrogen bonds between complementary bases
* Requires ATP
* One end acts as an attachment site for a specific a.acid (depends on anticodon)
* Anticodon contains 3 bases which are complementary to the codon for the a.acid it carries
42
What is rRNA?
* Combines with proteins to make ribosomes
| * Synthesised in the nucleolar organiser and then exported to the cytoplasm
43
What is transcription?
Conversion of the genetic code to a sequence of nucleotides in mRNA
44
Transcription process (excluding post-transcription)
* DNA unwinds and unzips and H bonds break due to helicase
* DNA acts as a template
* Bases are exposed in the antisense strand
* RNA polymerase catalyses the addition of free RNA nucleotides to form a complementary strand of mRNA
* Adjacent RNA nucleotides join by condensation reactions
* Bases of RNA are joined to produce a complete single-stranded molecule
45
Post-transcription process
* Hydrogen bonds between the two strands of DNA reform
* mRNA formed is known as pre-mRNA
* Introns are removed from pre-mRNA to form functional mRNA (from extrons)
* mRNA molecule leaves nucleus through the nuclear pore and travels to a ribosome in the cytoplasm
46
What is the role of helicase?
* Breaks hydrogen bonds that hold the double helix together
| * Exposes the bases in the antisense strand
47
What is the role of polymerase?
* Copies a DNA sequence into an RNA sequence
| * Proof reading
48
What is the central dogma of biology?
* DNA (replication)
* RNA (transcription)
* PROTEINS (translation)
49
What is the advantage of differential splicing?
It can join different combinations of exons together and produce different polypeptide s
50
What is purpose of transcription?
To transfer the code for the polypeptide from DNA to mRNA so it can be transported to the ribosome
51
What is the purpose of translation?
* tRNA is used to transfer amino acids to the ribosome
| * Translation is the conversion of the code in mRNA to a sequence of amino acids
52
What is activation?
* Specific amino acid joins to the amino acid attachment site on the tRNA molecule
* Requires ATP
53
Process of translation
•Large subunit of the ribosome has 2 binding sites so 2 RNA molecules can bind at a time
•The 2 a.acids carried by tRNA are connected by a peptide bond formed by a condensation reaction, catalysed by a ribosome enzyme (ATP is required)
•1st tRNA leaves ribosome and 2nd replaces it
•Another tRNA with the next a.acid in the sequence can then bind
•Codon on mRNA is complementary to the anticodon on the newly arrived tRNA molecule
-briefly form a codon-anticodon complex
•Ribosomes move along mRNA, reading each codon - specific a.acid is added to the growing polypeptide chain
•Translation stops when a stop codon is reached
•The 2 subunits of the ribosome separate and the polypeptide chain leaves the ribosome
54
What is a polyzone?
A chain of ribosomes carrying out translation
55
What is a point mutation?
•A mutation affecting only one or very few nucleotides in a gene sequence
56
What is a missense mutation? (Point mutation)
A point mutation which causes the amino acid to change
| -can be beneficial/harmless/deleterious
57
What is sickle cell anaemia? (Deleterious missense mutation)
* A mutation in coding for B chain of Hb
* Glutamic acid is replaced by Valine
* RBC becomes sickle shaped as Valine is hydrophobic
* RBC cannot carry enough O2 and can easily get stuck in the capillaries and block them
58
What is a nonsense mutation? (Point mutation)
There is an early stop codon in the mRNA which causes the protein to become truncated (shorter)
59
What is Duchenne muscular dystrophy? (Nonsense mutation)
Inherited by X chromosome so more common in men
60
What is a silent mutation? (Point mutation)
Does not change due to code being degenerate
61
What are frame shift mutations?
* Insertions and deletions (Indel mutations)
| * Cause a shift in the whole sequence - all codons are altered
62
What is Thalassemia? (Frame shift mutation)
•Deletion
63
Why is it important that RNA consists only of exons?
* Exons contain the code for proteins so are expressed
| * If introns are included a different protein structure would be produced
64
What effect would a mutation in an intron have on the protein?
No effect as introns are not translated
65
What effect would a mutation in an exon have on the protein?
It would cause a change in amino acid sequence, which causes a different amino acid in the polypeptide chain
66
Why does a ribosome contain the greatest percentage of RNA?
rRNA is a constituent of a ribosome
67
Why might the base sequence of mRNA be different from the sequence of pre-mRNA?
Introns in the pre-mRNA are spliced
68
Where does transcription occur in an animal cell?
In the nucleus
69
Why can deletion be bad?
* Affects all codons
| * More likely to affect the position of stop/start codons
