Topic 4.1 - The Genetic Code and Protein Synthesis Flashcards
Includes DNA, genes and chromosomes, and transcription and translation. (78 cards)
1
Q
What is the basic function of DNA?
A
Used to store genetic information
(all instructions organism needs to grow and develop from fertilised egg to adult)
2
Q
What is the main function of RNA?
A
Transfer genetic information from DNA to ribosomes
3
Q
What do ribosomes do?
A
Read RNA to make polypeptides in process called translation
4
Q
What are ribosomes made from?
A
RNA and proteins
5
Q
What 3 things does a nucleotide consist of?
A
- Nitrogen-containing organic base
- Pentose sugar
- Phosphate group
6
Q
What are monomers that make up DNA & RNA?
A
Nucleotides
7
Q
How are polynucleotides formed?
A
- Nucleotides join via condensation reaction between phosphate group of one nucleotide and sugar of another
- This forms a phosphodiester bond
8
Q
What is a chain of sugar and phosphates called?
A
Sugar-phosphate backbone
9
Q
What is the pentose sugar in a DNA nucleotide?
A
Deoxyribose
10
Q
Each DNA nucleotide has same sugar & phosphate group but a different…
A
nitrogen base
11
Q
Name the 4 possible bases in a DNA nucleotide
A
- Adenine (A)
- Thymine (T)
- Cytosine (C)
- Guanine (G)
12
Q
What is the pentose sugar in a RNA nucleotide?
A
Ribose
13
Q
Name the 4 possible bases in a RNA nucleotide
A
- Adenine (A)
- Uracil (U)
- Cytosine (C)
- Guanine (G)
14
Q
Describe how the structure of DNA is formed
A
- 2 DNA polynucleotide strands join together by hydrogen bonding between complementary base pairs
- 2 hydrogen bonds form between A & T, and 3 hydrogen bonds form between C & G
- 2 antiparallel polynucleotide strands twist to form DNA double-helix
15
Q
What does adenine pair with?
A
Thymine (A - T)
16
Q
What does cytosine pair with?
A
guanine (C - G)
17
Q
There is always _____ amounts of A & T in DNA molecule and C & G
A
EQUAL
18
Q
Describe the structure of RNA
A
Made from single polynucleotide chain = much shorter than most DNA polynucleotides
19
Q
Name 3 Types of RNA in every cell
A
- tRNA
- rRNA
- mRNA
20
Q
What does rRNA do?
A
Type of RNA that makes up ribosomes
21
Q
Explain how the structure of DNA is related to its functions (6)
A
- Double helix protects bases from corruption
- Large molecule so can store lots of genetic information
- Helix/coiled so compact
- Double stranded so replication can occur semi-conservatively
- (Weak) H-bonds for replication
- Many H-bonds so stable
- Complementary base pairing so accurate identical copies can be made
- Base sequence allows information to be stored
22
Q
Explain why the replication of DNA is described as semi-conservative (2)
A
- Each strand copied / acts as a template
- DNA has one new strand & one orginial
23
Q
Describe stage 1 of semi-conservative replication
A
DNA helicase breaks H bonds between bases = backbone is unzipped = helix unwinds
24
Q
Describe stage 2 of semi-conservative replication
A
Each original single strand acts as template for new strand:
Free nucleotides are attached to their complementary base on the backbone (orginal strand)
25
Describe stage 3 of semi-conservative replication
* Condensation reactions join nucleotides - catalysed by enzyme DNA polymerase
* H bonds form between bases (on original and new strands)
26
Describe stage 4 of semi-conservative replication
Each new DNA molecule contains one strand from original DNA molecule and one new strand
(Double strand twists again)
27
What are the differences between eukaryotic DNA and prokaryotic DNA?
Nuclear eukaryotic DNA is linear & associated with proteins. Whereas prokaryotic DNA is much shorter and circular, and not associated with proteins.
28
What is the name of the proteins that DNA associates with?
histones
29
What do histone proteins do?
Help support the DNA
30
DNA molecules and histone are coiled up very tightly to make _____ \_\_\_\_\_\_\_\_
compact chromosomes
31
What is the DNA in mitochondria and chloroplast (in eukaryotes) like?
Similar to prokaryotic DNA because its circular and shorter than DNA in nucleus & it's not associated with histone proteins
32
How does prokaryotic DNA fit into cells?
Condenses to fit in cell by supercoiling
33
What is a gene?
Sequence of DNA bases that codes for either a polypeptide or functional RNA
34
What do different polypeptides have?
They have different no. and order of amino acids
35
What determines the order of amino acids in a polypeptide?
The order of bases in a gene
36
What is each amino acid coded by?
A sequence of 3 bases in gene = called triplet or codon
37
What is meant by a cell's genome?
The complete set of genes in the cell
38
What is meant by a cell's proteome?
Full range of proteins that the cell is able to produce
39
Most DNA in eukaryotic cells _____ code for polypeptides
does not
40
In eukaryotic DNA, genes that code for _______ contain sections that...
In eukaryotic DNA, genes that code for _polypeptides_ contain sections that **don't code for amino acids**
41
What are introns?
Sections of DNA that don't code for amino acids
42
Can there be several introns within a gene?
Yes
43
What are exons?
Bits of gene that do code for amino acids
44
When are introns are removed?
During transcription
45
Prokaryotic DNA doesn't have \_\_\_\_
introns
46
What are multiple
tandem repeats?
DNA sequences that repeated over and over again
e.g. CCTTCCTTCCTT
47
Multiple repeats ____ code for amino acids & are called ______ \_\_\_\_
Multiple repeats _don't_ code for amino acids & are called _non-coding_ _repeats_
48
What is meant by the term allele?
Order of bases in each alleles is slightly different ∴ they code for slightly different versions of the same polypeptide (genes with the same locus)
49
What is homologous pair?
Pair of matching chromosomes: both chromosomes are same size & have same genes (BUT could have different alleles)
50
Where are alleles coding for the same characteristic found on chromsomes in a homologous pair?
Found at same fixed position (locus) on each chromosome in a homologous pair
51
Explain why DNA helicase is important in DNA replication (2)
* Breaks H-bonds
* (So) nucleotides can attach/strands can act as templates
52
Draw 2 nucleotides joining together
53
When is mRNA made?
During transcription
54
Describe the structure of mRNA
It's a single polynucleotide strand (& has groups of 3 adjacent bases)
55
What does tRNA do?
Carries amino acids that are used to make proteins to ribosomes
(involved in translation)
56
What does mRNA do?
Carries genetic code from DNA to ribosomes & is then used to make a protein during translation
57
Describe the structure of tRNA
It's a single polynucleotide strand that's folded into clover shape
58
How does tRNA stay in a clover shape?
H-bonds between specific base pairs hold it in shape
59
What does every tRNA molecule have? (2x)
* Anticodon at one end - specific sequence of 3 bases
* An amino acid binding site at other end
60
What is the main thing that happens in transcription?
mRNA copy of gene is made from DNA
61
In eukaryotic cells, where does transcription takes place?
Nucleus
62
Describe the stages in transcription
1. DNA helicase (in eukaryotes) breaks H-bonds between 2 DNA strands (in beginning of a gene)
2. Only one DNA strand acts as a template (to make mRNA copy)
3. Free bases in RNA nucleotides are attracted to exposed bases
4. Attraction occurs according to complementary base pairing (therefore mRNA strand becomes a complementary copy of DNA template strand)
5. RNA nucleotides are joined together by RNA polymerase
6. (In eukaryotes) mRNA moves out through nuclear pore
63
Where does transcription take place in prokaryotes?
Cytoplasm
64
When does the RNA polymerase stop making mRNA and detachs from DNA in transcription?
When RNA polymerase reaches a particular sequence of DNA called stop signal
65
Where does translation occur in both eukaryotes and prokaryotes?
At ribosomes in cytoplasm
66
What is the main thing occuring during translation?
Amino acids are joined together to make polypeptide chain, following the sequence of codons (triplets) carried by mRNA
67
Describe the stages in translation
1. mRNA moves into cytoplasm & attaches to ribosome
2. tRNA carry amino acids to it
3. Specific tRNA molecule for specific amino acid
4. Anitcodon of tRNA binds to complementary codon on mRNA (attaches by specific base pairing)
5. Peptide bond forms between amino acids
6. tRNA detaches and collects another amino acid
7. Ribosome moves along mRNA = forming a long polypeptide chain
68
What determines how the folded protein structure of protein will be?
Position of R groups in polypeptide chain
69
What is the genetic code?
Sequence of base triplets (codons) in mRNA which code for specific amino acids
70
Name 3 qualities of the genetic code
1. Non-overlapping
2. Degenerate
3. Universal
71
Describe how genetic code is non-overlapping
Each base triplet is read in sequence only once
72
Describe how genetic code is degenerate
Some amino acids are coded by more than one base triplet
e.g. tyrosine can be coded for by UAU or UAC
73
Describe how genetic code is universal
Same specific base triplets code for same amino acids in all living things
e.g. UAU codes for tyrosine in all organisms
74
What are start/stop signals (or codons)?
Triplets that tell the cell when to start/stop production of a protein
75
What is pre-mRNA?
mRNA strands containing introns and exons
76
Why does pre-mRNA contain introns and exons?
Introns and exons are both copied into mRNA during transcription
77
Name and describe the process how pre-mRNA is made into mRNA
Process called splicing occurs: introns are removed and exons join together = forming mRNA strands
78
What does transcription make in prokaryotes?
mRNA - it's produced directly from DNA without splicing
