4.2 DNA and protein synthesis Flashcards
1
Q
What is a gene?
A
(a) A sequence of DNA (nucleotides) bases that codes for a polypeptide.
2
Q
What is a genome?
A
The complete set of genes present in the cell.
3
Q
Is the full genome present within every cell?
A
Yes!
4
Q
Is every gene expressed in every cell?
A
No!
5
Q
What does which genes are expressed depend on?
A
The cell type
6
Q
What is the proteome?
A
The full range of proteins that a cell is able to produce
7
Q
Is the proteome normally larger than the genome of an organism?
A
Yes!
8
Q
Why is the proteome normally larger than the genome?
A
The large amount of post-translational modification of proteins
9
Q
Is each gene capable of producing multiple different proteins?
A
Yes!
10
Q
Why is each gene capable of producing multiple different proteins?
A
Alternative splicing
11
Q
Is RNA a polynucleotide?
A
Yes
12
Q
What bases does RNA contain?
A
A+U and C+G
13
Q
What sugar does RNA contain?
A
Ribose
14
Q
Is RNA double or single stranded?
A
Single
15
Q
What type of bonds are the sugar-phosphate bonds in RNA?
A
Covalent bonds
16
Q
What do the phosphodiester bonds link in RNA?
A
- The 5-carbon of one ribose sugar molecule, to the phosphate group of the same nucleotide.
- Which in turn is linked to the 3-carbon of the ribose sugar of the next nucleotide.
17
Q
Give an example of RNA:
A
mRNA
18
Q
Is mRNA single stranded?
A
Yes
19
Q
Does mRNA contain a sugar-phosphate backbone?
A
Yes
20
Q
mRNA contains exposed _______ bases.
A
Unpaired
21
Q
Is tRNA single or double stranded?
A
Single
22
Q
Does tRNA have a sugar phosphate backbone?
A
Yes
23
Q
What shape does tRNA have?
A
A folded shape.
24
Q
How is tRNA a folded shape?
A
There are hydrogen bonds between some of the complementary bases
25
Where do amino acids bind to tRNA?
A specific region of the molecule.
26
What is the specific anticodon found on the tRNA molecule complimentary to?
A specific codon on an mRNA molecule
27
What are the two stages of protein synthesis?
- Transcription
- Translation
28
Summary of transcription:
- DNA is transcribed
- An mRNA molecule is produced
29
Summary of translation?
- mRNA is translated - an amino acid sequence is produced.
30
Where does transcription occur?
Nucleus
31
What enzyme catalyses part of the DNA molecule being unwound?
Helicase
32
How can a DNA molecule be unwound?
By breaking the hydrogen bonds between the complementary base pairs.
33
What does helicase do (transcription)?
Unwinds part of the DNA molecule
34
What does unwinding part of the DNA molecule do?
Exposes the gene (that codes for a particular polypeptide) to be transcribed.
35
How is a complimentary copy of the code from the gene made?
By building a single-stranded nucleic acid molecule known as mRNA.
36
How is a complementary copy of the gene made?
- Free activated RNA nucleotides pair up.
- With their complementary bases on one strand of the DNA molecule.
37
How do the free activated RNA nucleotides pair up?
Via hydrogen bonds
38
What enzyme bonds the sugar-phosphate groups of these RNA nucleotides together?
RNA polymerase
39
What does RNA polymerase do?
Bonds the sugar-phosphate groups of these RNA nucleotides together
40
What does RNA polymerase form?
The sugar-phosphate backbone of the mRNA molecule.
41
What happens once the gene has been transcribed?
- The hydrogen bonds between the mRNA and DNA strands break
- The double stranded DNA molecule re-forms
42
How does the mRNA molecule leave the nucleus?
Via a pore in the nuclear envelope.
43
When does the mRNA molecule leave the nucleus?
Once the gene has been transcribed.
44
Do free activated RNA nucleotides pair up with exposed bases on one or both strands of the DNA molecule?
One
45
What is the template strand?
The strand of DNA with which free activated RNA nucleotides pair up with its exposed bases.
46
What is the non-template strand?
The strand of the DNA molecule that is not transcribed
47
Can the genome in EUKARYOTIC cells contain non-coding section?
Yes!
48
What are the 2 places the non-coding DNA can be found in the genome in eukaryotic cells?
- Between genes
- Within genes
49
How is non-coding DNA found BETWEEN genes?
As non-coding multiple repeats
50
How is non-coding DNA found WITHIN genes?
As introns
51
When is pre-mRNA produced?
During transcription, when a gene is transcribed (all introns and exons)
52
What does pre-mRNA contain?
The introns and exons of a certain gene
53
When does splicing occur?
Before the pre-mRNA exits the nucleus
54
What happens to the non-coding sections during splicing?
They are removed
55
What happens to the coding sections during splicing?
They are joined together
56
What does mRNA contain (after splicing)?
Only exons (the coding sequences)
57
What is alternative splicing?
- The exons of genes can be spliced in many different ways.
- To produce different mature mRNA molecule.
58
What does mRNA mean?
A single eukaryotic gene can code for more than one polypeptide chain.
59
Where does translation occur?
In the cytoplasm
60
What does mRNA do once it has left the nucleus?
It attaches to a ribosome
61
Where are tRNA molecules located?
Free, in the cytoplasm
62
What is on either end of a tRNA molecule?
- On one end there is an anticodon.
- On the other, there is a region where a specific amino acid can attach
63
How many different tRNA molecules are there?
At least 20
64
What do tRNA molecules bind with?
Their specific amino acids
65
What do the tRNA molecules do once they have bound with their specific amino acids?
They bring them to the mRNA molecule on the ribosome
66
What does the anticodon on each tRNA molecule bind to?
The complementary codon on the mRNA molecule
67
How many tRNA molecules fit onto a ribosome at one time?
2
68
Because 2 tRNA molecules can fit on the ribosome at one time, what happens to the amino acids?
2 amino acids are brought side by side
69
What bond is formed between the 2 side-by-side amino acids?
A peptide bond
70
What does the formation of a peptide bond require?
Energy, in the form of ATP
71
When does translation continue until?
A stop codon is reached
72
What is a triplet?
A sequence of three DNA bases that codes for a specific amino acid
73
What is a codon?
Sequence of three mRNA bases that codes for a specific amino acid
74
What is an anticodon?
A sequence of three tRNA bases that are complementary to a codon
75
Is the genetic code degenerate, and what does it mean?
Yes - multiple mRNA codons can code for the same amino acid
76
What does the fact that the genetic code is degenerate mean?
A change in the genetic code doesn't necessarily result in a change in the amino acid sequence
77
What does the start codon do?
- Marks the start of the protein
- Therefore initiates the process of translation (from the right location).
78
What does the stop codon do?
Causes translation to terminate at the end of the protein
79
Does the stop codon code for any amino acids?
NO
80
Is the genetic code non-overlapping, and what does this mean?
Yes - each base is only read once in the codon it is part of.
81
Describe two differences between the structure of a tRNA molecule and the structure of an mRNA molecule.
- tRNA is 'clover leaf shape', mRNA is linear
- tRNA has hydrogen bonds, mRNA does not
82
Describe and explain a difference in the structure of pre-mRNA and mRNA.
- mRNA has no introns/has (only) exons
- Due to splicing
83
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation.
- tRNA brings specific amino acid to ribosome
- Anticodon on tRNA binds to codon on mRNA
- Amino acids join by condensation reaction
84
Describe how mRNA is produced from an exposed template strand of DNA.
- Free RNA nucleotides form complementary base pairs
- Phosphodiester bonds form
- Catalysed by RNA polymerase
85
Define the term exon.
Base sequence coding for a polypeptide
86
Describe how mRNA is formed by transcription in eukaryotes. (LONG)
- Hydrogen bonds between DNA bases break
- One DNA strand acts as a template
- Free RNA nucleotides align by complementary base pairing
- Uracil base pairs with adenine
- RNA polymerase joins adjacent RNA nucleotides
- By phosphodiester bonds
87
Describe how a polypeptide is formed by translation of mRNA.
- mRNA attaches to ribosomes
- tRNA anticodons bind to complementary mRNA codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds (using ATP)
- tRNA released after amino acid joined to polypeptide
- The ribosome moves along the mRNA to form the polypeptide
88
What is the proteome of a cell?
The full range of different proteins that a cell is able to produce
89
Describe the process of transcription (8 steps).
DNA helicase unwinds DNA double helix
by breaking the hydrogen bonds between the base pairs and strand seperates
Only one strand acts as a template.
Free RNA nucleotides align next to their complementary bases on the template strand and form temporary hydrogen bonds (uracil replaces thymine).
RNA polymerase joins the adjacent nucleotides together by forming phosphodiester bonds in a condensation reaction.
RNA polymerase reaches stop codon, mRNA (prokaryotes) or pre-mRNA (eukaryotes) detaches from DNA.
This forms pre-mRNA in eukaryotic cells and mRNA in prokaryotic cells.
Then the pre-mRNA is spliced (introns removed) to form mRNA.
90
Describe the process of translation (8 steps).
1. mRNA attaches to ribosomes after leaving nucleus through cytoplasm
2. tRNA anticodons bind to complementary mRNA codons
3. tRNA brings a specific amino acid
4. Amino acids join by peptide bonds between 2 amino acids- requires ATP
5. Amino acids join together with the use of ATP - by condensation reaction
6. tRNA released after amino acid joined to polypeptide
7. continue until stop codon
8. The ribosome moves along the mRNA to form the polypeptide
91
Mutation 1 leads to the production of a non-functional protein. Explain why. (3)
(Mutation) changes triplets
Changes amino acid sequence
Affects hydrogen / ionic / sulfur bond
Changes tertiary structure of protein
92
give the two types of ,molecules forms which a ribosomes is made from
rRNA and protein
93
give 4 structural differences between a DNA molecule and an MRNA molecule
DNA has deoxyribose, mRNA has ribose;
DNA has thymine, mRNA has uracil;
DNA long, mRNA short;
DNA is double-stranded, mRNA is single-stranded
Accept ‘double helix’ for ‘double stranded’ and ‘single helix’ for ‘single stranded’
DNA has hydrogen bonds, mRNA has no hydrogen bonds
OR
DNA has (complementary) base pairing, mRNA does not;
94
name 2 biological molecules that can be coded for by a gene, dont include a polypeptide or a protein
pre mRNA
rRNA
tRNA
95
(c) Scientists investigated the structure of the endoplasmic reticulum.
The table below shows some of the scientists’ results.
Type of endoplasmic reticulum Percentage of endoplasmic reticulum made of phospholipids
Rough 46.8
Smooth 52.5
Use the data in the table to suggest how the structure of rough endoplasmic reticulum is different from the structure of smooth endoplasmic reticulum and how this is related to their functions.
Less phospholipids in rough OR More protein/glycoprotein in rough OR Presence of ribosomes in rough;
Rough ER - production/transport of proteins;
Smooth ER - production/modification/packaging/transport of lipids;
96
(a) Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation.
a) 1. tRNA brings specific amino acid (to ribosome);
2. Anticodon (on tRNA) binds to codon (on mRNA);
3. Amino acids join by condensation reaction (using ATP).
97
(b) Describe how the production of messenger RNA (mRNA) in a eukaryote cell is different from the production of mRNA in a prokaryote cell.
______________________
1. Pre-mRNA (only) produced in eukaryote;
2. Splicing only occurs in eukaryote;
3. Introns removed in eukaryote OR introns not present in prokaryote.
98
(c) Scientists produced a short, single-stranded, artificial nucleic acid, called PNA. The PNA binds to a small section of DNA.
The scientists introduced PNA into cells and discovered that these cells produced less mRNA than cells that did not contain PNA.
Suggest how PNA affected the transcription of the section of DNA.
1. PNA is complementary to DNA;
2. Preventing/reducing RNA polymerase activity/binding.
(d) 1. Releases/provides energy;
2. Peptide bonds form between amino acids OR amino acid joins to tRNA.
99
(d) Describe the role of ATP in the process of translation in protein synthesis.
1. Releases/provides energy;
2. Peptide bonds form between amino acids OR amino acid joins to tRNA.
100
(c) Describe two differences between the structure of a tRNA molecule and the structure of an mRNA molecule.
1. tRNA is 'clover leaf shape', mRNA is linear;
2. tRNA has hydrogen bonds, mRNA does not;
3. tRNA has an amino acid binding site, mRNA does not;
4. tRNA has anticodon, mRNA has codon.
101
(d) In a eukaryotic cell, the structure of the mRNA used in translation is different from the structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecule
d) 1. mRNA fewer nucleotides OR Pre-mRNA more nucleotides;
2. Because of splicing.
102
(a) Describe how mRNA is produced from an exposed template strand of DNA.
Do not include DNA helicase or splicing in your answer.
1. Free RNA nucleotides form complementary base pairs;
2. Phosphodiester bonds form;
3. By action of RNA polymerase
