Lecture 5 - Part 2 - Transcription and translation Flashcards
1
Q
Why look at transcription and translation
A
It explains how nucleic acids construct proteins
2
Q
How many chromosomes does each human have
A
46 chromosomes ( 23 pairs )
3
Q
What is a chromosome and how is it formed
A
- ## DNA, wrapped up and packaged, wound around other proteins into these X shaped parcels and twisted/further folded
4
Q
What are histones
A
Proteins that condense/ coil and structure the DNA of eukaryotic cell nuclei into units called nucleosomes
5
Q
What are the core histones
A
H2A, H2B, H3 and H4 `
6
Q
What does the histone octamer consist of
A
2 copies of each histone protein
7
Q
What is the nucleosome core formed of
A
Two H2A-H2B dimers and a
H3-H4 tetramer
8
Q
How is nucleosome formed and what does each one consist of
A
DNA coils twice aroundtheoctamer
8 histone proteins
9
Q
What anchors nucleosome together
A
Histone H1
10
Q
What are nucleotides
A
Building blocks of nucleic acids
11
Q
What is the structure of nucleotide
A
-Nitrogenous base
-5C sugar can be..
Ribose = RNA
Deoxyribose = DNA
-Phosphate group
12
Q
What gives the structral element of nucleotide
A
Sugar and phosphate
13
Q
What does base do
A
Encodes genetic information
14
Q
What’s the sugar for DNA
A
Deoxyribose
15
Q
What’s the sugar for RNA
A
Ribose
16
Q
What is the 5 carbon sugar and how are carbon atoms labelled
A
Pentose ring
Carbon atoms in pentose ring labelled 1-5 clockwise from Oxygen
17
Q
How is ribose and deoxyribose struucturally different
A
For Ribose -OH group at 2’ postiion
18
Q
What determines genetic information
A
Sequence of bases on DNA
19
Q
What carbon number is phosphate group attached to
A
5th carbon
20
Q
What are the 4 bases in DNA
A
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
21
Q
What are bases classed as
A
Purines or Pyrimadines
22
Q
Which bases are Purines
A
Adenine and guanine
23
Q
Which bases are Pyrimadines
A
cytosine and thymine
24
Q
How many interlocking nitrogen-containing rings does purine contain
A
Two
25
How many interlocking nitrogen-containing rings does pyramidine contain
One
26
What carbon number are bases joined to sugar
C1
27
What bond is formed between phosphate group and ribose sugar
Phosphodiester bond
28
How are DNA bases on strands held together
Hydrogen bonds
29
Which bases are complementary
A + T
| C + G
30
How many hydrogen bond between A + T
2
31
How many hydrogen bond between C + G
3
32
Properties of the DNA double Helix
- Two helical polynucleotide chains are coiled around a common axis
- The chains run in opposite directions – antiparallel
- Complementary bases are held together by hydrogen bonds on the inside
- Planes of the Bases are at 90° to axis
- A phosphate-deoxyribose polymer composes the outside backbone of the DNA = phosphodiester bonds
- Nitrogenous bases are covalently bonded to the 1' carbon of the deoxyribose
- The individual hydrogen bonds are weak but the large number of them confer stability
33
Is all DNA contained within chromosomes
No
34
What is independent in terms of DNA
Mitochondria
| They contain their own DNA which encode the mitochondrial proteins and some ribosomal RNA.
35
How many genes does mitochondria contain
37
| Essential for normal mitochondrial function
36
Uses of genes in mitochondria
- Direct the synthesis of enzymes involved in oxidative phosphorylation (ATP production)
- Synthesis of transfer RNA (tRNA)
- Synthesis of ribosomal RNA (rRNA)
- These RNA’s help assemble amino acids into functioning proteins
37
How does our genetic code translate into what we are
By transcription and translation
38
Summary of transcription and translation
The genetic code from DNA is ‘copied’ (transcribed) into shorter sequences (RNA), which are then ‘read’ (translated) by a ribosome which generates a sequence of amino acids, the chains that form proteins.
39
What is RNA
Sequence of nucleotides
40
How is RNA different from DNA
- Ribose sugar rather than deoxyribose
- RNA is single stranded
- Thymine is substituted for Uracil
41
What base does Uracil replace
Thymine
| Cytosine and Uracil - pyramidine - bases joined to C1 of ribose sugar
42
Transcription and translation flow diagram
DNA - mRNA - Polypeptide
43
What is transcription
The production of messenger RNA (mRNA) by the enzyme RNA polymerase, and the processing of the resulting mRNA molecule.
44
What are the 4 steps of Transcription
Initiation.
Elongation.
Termination.
Processing.
45
Transcription - Initiation
The DNA molecule unwinds and separates to form a small open complex. RNA polymerase (enzyme) binds to the promoter of the template strand.
46
What does transcription factors do
Bind to the TBP which binds to TATA box (promoter)
47
Transcription - elongation
RNA polymerase II moves along the template strand, synthesising an mRNA molecule
Phosphate Group - Joins 3’ to 5’ Carbon with a Phosphodiester bond
48
Transcription - Termination
Addition of additional adenine nucleotides at the 3' of the RNA transcript (a process referred to as polyadenylation). Creates the poly (A) tail
- Gets to end of gene that it wants to read
- Stops reading gene and adds a load of adenine's ( poly - A - tail to the end of RNA - polyadenylation
49
What's polyadenylation
Addition of adenine nucleotides at the 3' of the RNA transcript
50
Transcription - Processing
- RNA splicing removes Introns
| - mRNA) is produced, this can now leave the nucleus through nuclear pores
51
What are genes composed of
Introns and exons
52
What are introns
non-coding sequences - not essential for making protein
53
What are exons
Coding sequences - are expressed - produce proteins
54
What does splicing do
Remove introns - non coding regions from RNA and seal blocks together
55
What's translation
mRNA that has left the Nucleus is used as a TEMPLATE to assemble a chain of amino acids (polypeptide) with a specific sequence.
56
What 2 components does translation require
- Ribosomes
| - tRNA
57
What are 4 steps of translation
Initiation.
Elongation.
Termination.
Post-translation processing of the protein
58
What does translation involve
- Conversion of the nucleotide sequence of mRNA into an amino acid sequence of a protein
59
What is ribosome made of
65% rRNA and 35% protein
60
Where places are ribosome found
Nuclear envelope
R.E.R
Free floating in cytosol
61
Function of ribosomes in translation
- Catalyse the assembly of protein chains (they’re enzymes)
- Read mRNA sequences, and bind tRNA which are bound in turn to an amino acid.
- Place amino acids next to each other in a sequence that will form the protein read from the mRNA code. You
62
What do ribosomes consist of
Large and small subunits
63
What do ribosomes have
Binding site for mRNA and 3 binding sites for tRNA
-Combination of R groups sticking out from protein creates environment with 3 specific pockets which will recruit something in, bind to it and pass onto next pocket
64
Function/role of tRNA in translation
Helps decode mRNA strand
| functioning at the binding sites in ribosomes during translation
65
What are proteins built from
Amino acids, specified by 3 nucleotide mRNA sequences called codons
66
What does each codon represent
A particular amino acid and each codon is recognised by specific tRNA
67
Structure of tRNA
- 3 hairpin loops
- One of these hairpin loops contains a sequence – the anticodon – complimentary to the mRNA codon
- Each tRNA is covalently linked to its corresponding amino acid
68
What happens when tRNA recognises and binds to its corresponding codon in the ribosome
The tRNA transfers the appropriate amino acid to the end of the growing amino acid chain
69
What do tRNA and ribosome do
Continue to decode the mRNA molecule until the entire sequence is translated into a protein
70
Translation - Initiation
- The small ribosome subunit binds at the 5' end of the mRNA molecule and moves in a 3' direction.
- It keep moving until it reads a start codon (AUG).
- It then forms a complex with the large unit of the ribosome complex and recruits a tRNA.
71
Trancription - Elongation
- Following codons of the mRNA chain determine which tRNA molecule next is recruited into the ribosome. This enters binding site A as the first tRNA moves into site P.
- A new peptide bond is formed between amino acids at other end of tRNAs
- The small subunit moves a distance of a codon along the mRNA chain ejecting the spent tRNA molecule
- The next tRNA molecule binds to the A-site on the ribosome
- Steps continue and create a polypeptide
72
Translation - Termination
- vTranslation in terminated when the ribosomal complex reads a stop codon (either UAA, UAG, UGA).
- This codon binds a release factor and results in hydrolysis of the last amino acid (–COOH) when the ribosomal release factor is read
- The release factor disconnects the polypeptide from the tRNA in the P-site
- The ribsome dissociates into its two separate subunits
73
Gene expression
- Multiple identical RNA copies can be made from the same gene
- Each RNA molecule can direct the synthesis of many identical protein molecules
- Each gene can be transcribed and translated with different efficiency
- RNA polymerase requires transcription factors - genes are up or down regulated by transcription factors
- Transcription and translation are regulated
74
Controlling gene expression - Transcription control
- The most common type of genetic regulation
- Turning on and off of mRNA formation
- The rate at which DNA is being read and turned into RNA
- Regulated by availability of transcription factors
75
Controlling gene expression - Post - Transcription control
Regulation of the processing of a pre-mRNA into a mature mRNA
- Regulation of splicing enzymes
76
Controlling gene expression - Translational Control
Regulation of the rate of Initiation - availability of ribosomes, tRNA - limit how much RNA into protein
77
Controlling gene expression - Post Translational Control
Regulation of the modification of an immature or inactive protein to form an active protein
i.e. how it processes through golgi and modified with lipids and sugars
78
What happens to genetic material ( chain )
It's split up into 20,000 different regions - each one = gene - contains genetic code to make one protein
79
What does TATA box represent
Binding/promoter region of genetic code
80
What do transcription factors do
Recruit enzyme - RNA polymerase II
81
What does RNA polymerase II do
- Opens up DNA and starts transcription process - starts reading of genetic code and produce RNA chain
- Binds to the promoter of the template strand
82
What does RNA polymerase II do in elongation
Unwinds double helix and reads 1 chain of DNA and recruits in free floating nucleotides and pieces in complementary base. e.g. C and G
83
What happens once the nitrogenous base has binded to its complementary base
Creates a chain of RNA which is complementary to DNA sequence
84
How are RNA's binded together
Condensation reaction
85
What does splicing produce
mRNA - template strand
86
What does mRNA bind with during translation
Ribosome
87
What is mRNA used for in translation
A template to produce protein
88
What does ribosome recruit
tRNA
89
What is gene
Sequence of bases
90
How are bases read
In groups of 3 - codon - triplet
91
What are triplets of bases referred to in mRNA
Codons
92
What is each codon specific for
Certain amino acid
93
Where is RNA produced
Nucleus
94
What creates the hairpin loops in tRNA
Hydrogen bonding
95
What is anticodon
Sequence of 3 bases in a row which then specific sequence.
96
How many different types of tRNA's
64
97
What is start codon for every protein in body
AUG
98
What happens when start codon is read
Ribosome brings in tRNA and starts translation
99
When does termination happen
When there's a stop codon
100
What do stop codon's represent
Not amino acid, instead its represents tRNA not bind to amino acid
101
What is post translation processing of protein
Can be modified afterwards
| Go into golgi apparatus - add sugars
102
Why regulate gene expression ( transcription and translation)
Don't need every protein identified in genetic material being produced at the same rate all the time - inefficient
103
What is one way of regulating gene expression
Binding of transcription factors - change rate at which RNA is being produced and therefore rate at which protein is being produced from that
104
How are transcription factors activated
- Cleaving off region
| Phosphorylating/dephosphorylating
105
What happens when transcription factors are active
Migrate into nucleus and bind to DNA and initiate transcription
