Protein synthesis, DNA and Genetic Variation- ARN Flashcards
(65 cards)
1
Q
What is a gene
A
A section of DNA that codes for the sequence of amino acids in a polypeptide and functional RNA.
2
Q
True or False: All sections of DNA code for genes
A
False
3
Q
What is meant by the locus of a gene?
A
The location of a gene on a strand of DNA or a chromosome
4
Q
What are the four features of the genetic code?
A
Universal
Non-overlapping
Degenerate
Triplet Code
5
Q
Why is the genetic code described as universal?
A
The same codons code for the same amino acids in all living organisms
6
Q
Why is the genetic code described as non-overlapping?
A
Each triplet is separate from each other, so each base is only read once.
7
Q
Why is the genetic code described as degenerate?
A
Lacks a pattern as more than one triplet can code for the same amino acid
8
Q
Why is the genetic code described as having a triplet code?
A
Three bases code for one amino acid in a 5’ to 3’ direction
9
Q
What are introns?
A
Non coding sequences of bases
10
Q
What is a codon?
A
Triplet of bases on mRNA that codes for a specific amino acid.
11
Q
What are exons?
A
Coding sequences of bases
12
Q
What is splicing?
A
The process where introns in a pre-mRNA molecule are removed, and the remaining exons are joined together to form mature mRNA
13
Q
What is a chromosome?
A
A package of DNA containing part of or all the genetic material of an organism
14
Q
Differences between eukaryotic and prokaryotic DNA
A
- Eukaryotic DNA is long, prokaryotic is short
- Eukaryotic DNA linear, prokaryotic DNA is circular
- Eukaryotic DNA is associated with histones, prokaryotic DNA is not
- Eukaryotic DNA has introns, prokaryotic DNA doesn’t
- Eukaryotic DNA is in a nucleus ,prokaryotic DNA is not
15
Q
Do chloroplasts have introns?
A
Yes
16
Q
Properties of Prokaryotic, Mitochondrial and Chloroplast DNA
A
- Short
- Circular
- Not associated with histones
- No introns in prokaryotic and mitochondrial DNA
- No nucleus
17
Q
What is transcription?
A
Transcription Is the process of making mRNA from a DNA template strand.
18
Q
Describe the process of transcription
A
- DNA Helicase separates strands by breaking H bonds between bases
- Free RNA nucleotides are attracted to the template strand
- Complementary base pairing (A to T, C to G, U to A, G to C)
- Adjacent RNA nucleotides are joined by RNA Polymerase
- Hydrogen bonds reformed.
- pre mRNA is formed. Pre-mRNA is the first form of RNA created through transcription in protein synthesis. It contains introns and exons.
- Pre mRNA is spliced to form mRNA
19
Q
Why is there no splicing involved in the transcription of prokaryotic DNA?
A
There are no introns
20
Q
What is an anticodon?
A
Triplet of bases on tRNA that is complimentary to a codon on mRNA
21
Q
What is tRNA?
A
Transfer RNA is a small RNA molecule that carries specific amino acids to the ribosome. Its anticodon is specific to the amino acid it carries. It is folded by H bonds and has a clover leaf shape
22
Q
Describe the process of translation
A
- mRNA associates with a ribosome
- Ribosome finds start codon
- tRNA carries a specific amino acid (attaching an amino acid to tRNA requires ATP)
- Anticodon on tRNA matches with a codon on mRNA.
- Ribosome moves onto next codon
- Process is repeated and amino acids join by
peptide bonds, using energy from ATP.
23
Q
What is meiosis?
A
Cell division to form gametes
24
Q
What is a gamete?
A
A haploid sex cell
25
What is a haploid?
A cell that contains a single set of unpaired chromosomes, half the number of chromosomes or one of each homologous pair. It is represented by n
26
What is a diploid?
A cell with a complete set of chromosomes. Represented by 2n
27
What is fertilisation?
Fusion of two haploid gametes to form a zygote
28
What is an allele
A variant of a gene at a specific locus on a chromosome
29
Features of meiotic cell division that contribute to genetic variation
- Chiasmata/crossing over (which produces recombinant DNA),
- Independent assortment
- Random segregation.
29
Why must gametes be haploids?
In order to restore the chromosome number at fertilisation
30
Differences between meiosis and mitosis
- Meiosis forms gametes, mitosis is for growth and repair
- 2 divisions in meiosis, 1 in mitosis
- 4 daughter cells as a result of meiosis, 2 for mitosis
- Genetically diverse daughter cells in meiosis, genetically identical cells in mitosis
31
Prophase I:
- Chromosomes condense and become visible then they pair up with their homologous pairs.
- Homologous pairs pair up and transfer sections of their DNA; this is known as crossing over.
- Crossed over chromosomes are known as chiasmata.
- Once crossed over they are referred to as recombinant chromosomes
32
How does crossing over add genetic variation?
Crossing over/chiasmata add genetic variation as sister chromatids are no longer identical.
33
Describe crossing over or the formation of chiasmata
Homologous pairs pair up and transfer sections of their DNA
34
What is meant by chiasmata
Crossed over chromosomes
35
What is meant by recombinant chromosomes?
Chromosomes after they have crossed over and transferred DNA
36
Metaphase I:
- Chromosomes line up in pairs in the middle of the cell and independent assortment occurs.
- Spindle fibres form and attach to chromosomes by their centromere.
37
What is independent assortment?
Independent assortment is the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I.
38
What is random segregation?
The random distribution of homologous chromosomes to different gametes during meiosis
39
Anaphase I
Homologous pairs are pulled to opposite poles of the cell, unlike mitosis where spindle fibres separate sister chromatids .
40
Telophase I
Cytokinesis, 2 cells form with 23 double chromosomes. After meiosis I, you’re down to 2 haploid cells.
41
Prophase II
Chromosomes condense and become visible.
42
Metaphase II
Chromosomes line up in the middle of the cell and attach to spindle fibres by their centromeres.
43
Anaphase II
Spindle fibres contract and separate sister chromatids, pulling them to opposite poles of the cell
44
Telophase II
Cytokinesis, 2 cells form with 23 single arm chromosomes. After meiosis II, you have 4 haploid cells.
45
What is non-disjunction?
Failed separation of homologous pairs or sister chromatids leading to the incorrect number of chromosomes in gametes.
46
Is non-disjunction more severe in meiosis I or II and why?
Non-disjunction in meiosis 1 is more severe as it means every daughter cell is affected, whereas in meiosis 2 it is less severe.
47
What is a mutation?
Random change in the DNA base sequence
48
How can a mutation in the DNA base sequence affect the function of a protein
A change in the base sequence alters the primary structure of a protein and therefore can affect its final shape and function
49
Mutations are most likely to occur during which stage of the cell cycle
During interphase as this is when DNA replication occurs
50
What is substitution mutation?
When one base is substituted for another
51
Insertion mutation
An extra base is inserted into the sequence. These mutations are worse as it alters all following codons, leading to a frameshift
52
Deletion mutation
A base is deleted from the sequence. This also leads to a frameshift
53
Which types of mutation lead to a frameshift?
Insertion and mutation
54
Mutagenic agents are:
Things that increase the chances of mutations
55
Examples of mutagenic agents
* High energy radiation
* Alpha/Beta/Gamma radiation
* X-rays/cosmic rays
* UV light
* Carcinogens e.g. smoking/alcohol
* Mustard gas
* Tar
56
Reasons mutations could be harmless
* The genetic code is degenerate, so if a base is substituted for example, it could still code for the same amino acid.
* Occur in introns.
57
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. (6 marks)
1. Homologous chromosomes pair up/Bivalents form
2. Crossing over occurs/Chiasmata form
3. This produces new combinations of alleles
4. Chromosomes separated by spindle fibres
5. At random (due to independent assortment)
6. Produces varying combinations of chromosomes
7. Chromatids separated at meiosis 2
58
Describe the process of crossing over and explain how it results in genetic diversity. (4 marks)
1. Homologous chromosome pairs associate
2. Chiasmata form
3. Sections of alleles are exchanged
4. Producing new combinations of alleles
5. Producing recombinant chromosomes
59
Describe how messenger RNA is produced in a plant cell (5 marks)
1. The DNA strands separated by DNA helicase breaking the H bonds.
2. Only template strand is used to make mRNA
3. Complementary base pairing
4. Adjacent RNA nucleotides joined by RNA polymerase
5. Pre-mRNA forms
6. Splicing/introns removed to form mRNA.
60
Contrast the structure of DNA and mRNA (3 marks)
1. DNA is double stranded, mRNA is single stranded
2. DNA is very long, mRNA is short
3. Thymine in DNA, Uracil in mRNA
4. Deoxyribose vs Ribose
5. DNA has base pairing mRNA doesn’t
6. DNA has introns, mRNA doesn’t
61
Starting with mRNA in the cytoplasm describe how translation leads to the production of a polypeptide. Do not include description of transcription and splicing (6 marks):
1. mRNA associates with a ribosome
2. Ribosome finds start codon
3. tRNA carries a specific amino acid
4. Anticodon on tRNA complementary to the codon on mRNA attaches
5. Ribosome moves onto next codon
6. Process repeated and amino acids join by peptide bonds using energy from ATP
62
Describe the role of tRNA in the process of translation (3):
1. tRNA anticodon complementary to codon
2. tRNA brings specific amino acid to ribosome
3. Allows for correct sequence of amino acids along polypeptide
63
Give 2 differences between the structure of mRNA and tRNA (2)
1. mRNA is longer/has more nucleotides
2. mRNA is a straight molecule, tRNA is a clover leaf shape
3. mRNA contains no base pairs/H bonds, but tRNA has some paired bases/H bonds
4. Many different mRNAs but only few (20) tRNAs
5. mRNA has no amino acids binding site but tRNA does
6. tRNA has anticodons, mRNA doesn’t
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