Gene expression from gene to protein Flashcards
1
Q
Gene expression
A
the process by which DNA directs the synthesis of proteins through RNA through 2 stages
- transcription and
- translation
2
Q
What do gene sequences encode for
A
RNA
3
Q
What does RNA typically encode for?
A
Synthesis of proteins
4
Q
3 stages of transcription:
A
- Initiation
- Elongation
- Termination
5
Q
Initiation of translation (3)
A
- ribosomal subunit binds with initiator tRNA and mRNA
- the subunit moves along the mRNA until it reaches the start codon signalled for by (AUG) which codes for Met
- Initiation factor proteins bring in the large subunit of the ribosome to complete the translation initiation complex
6
Q
Elongation (translation)
A
- the ribosome moves along the mRNA, reading codons and adding the corresponding amino acids to the growing polypeptide chain
- Translocation occurs, moving tRNA from A to P to E to be released
7
Q
Termination (translation)
A
- When the ribosome reaches a stop codon its A site accepts a release factor
- the release factor promotes hydrolysis of the bonds and frees the polypeptide
- ribosomal subunits dissociate
8
Q
Initiation (transcription)
A
- starts at the promoter
- RNA polymerase binds to promotor and unwinds section of DNA
- RNA synthesis is initiated
9
Q
Elongation steps (transcription)
A
- RNA polymerase moves along the DNA strand, “unzipping” the DNA 10-20 bases at a time and elongating the RNA transcript
- Nucleotides are added to the 3’ end
- A gene can be transcribed simultaneously by several RNA polymerases
- DNA reforms its double helix
10
Q
How fast is transcription in eukaryotes?
A
40 nucleotides per second
11
Q
Termination (transcription) in Bacteria vs Eukaryotes
A
RNA polymerase releases DNA and RNA transcript is free.
Bacteria:
- RNA polymerase stops transcription at the end of the terminator
- mRNA can be translated without further modification
Eukaryotes:
- Polyadenylation signal sequence added to the tail and the transcript is released 10-35 nucleotides after.
12
Q
Hydrolysis
A
- where a H2O molecule is added to the mRNA strand instead of an amino acid
- this breaks the bond and release the protein (amino acid chain).
13
Q
Transcription
A
the transfer of information from DNA to messenger RNA (mRNA).
14
Q
Translation
A
- synthesis of a protein under instruction from mRNA
- transfers information from mRNA to a polypeptide, changing from the language of nucleotides to that of amino acids.
15
Q
Ribosomes are …
A
- the sites of translation of mRNA into proteins
- ( synthesis of a polypeptide. )
16
Q
Messenger RNA (mRNA)
A
a type of RNA (synthesized using a DNA template) that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.
17
Q
Primary transcript
A
the initial RNA transcript of any gene.
18
Q
Triplet code
A
a sequence of three nucleotides (a triplet) in DNA or mRNA that codes for a specific amino acid
19
Q
Template strand
A
one strand from the DNA strands that provides the pattern (or template) for the sequence of nucleotides in an RNA transcript.
20
Q
Codon
A
- 3 mRNA bases
- specifies amino acid
- customarily written in the 5’ to 3’ direction.
21
Q
Reading frame
A
- the specific way a sequence of nucleotides in DNA or RNA is divided into codons for translation into a protein.
- There are three possible reading frames, and the correct one is established by a start codon (usually AUG
22
Q
Why is the correct reading frame important?
A
So that the protein product is produced correctly
23
Q
Promoter
A
the DNA sequence where RNA polymerase attaches and initiates transcription.
24
Q
RNA polymerase
A
- Enzyme that catalyses RNA synthesis
- joins RNA nucleotides that are complementary to the DNA template strand in a 5’ to 3’ direction, with Uracil replacing thymine
25
Terminator
the sequence that signals the end of transcription.
26
Transcription unit
the sequence of DNA that is transcribed into one RNA molecule.
27
Start point
the nucleotide where RNA synthesis actually begins.
28
Transcription factors
- Proteins that can bind to DNA sequences, regulating whether transcription can occur or not and hence controlling which genes are expressed and when
29
Transcription initiation complex
- Assembly of transcription factors that forms at the promotor region of a DNA strand.
- Initiates RNA synthesis
30
TATA box
- a specific DNA sequence at the promoter region of Eukaryotic genes that signals initation of transcription
31
RNA processing
both ends of the primary transcript are altered and certain interior sections of the RNA molecule are cut out and the remaining parts are spliced together.
32
Poly-A-tail
a string of adenine nucleotides that are added to the 3' end of the RNA transcript in the termination stage.
- added for protection
33
5' cap
a modified form of guanine (G) nucleotide added onto the 5' end after transcription of the first 20-40 nucleotides.
34
Introns
- Long segments of noncoding nucleotide sequences.
- They are intervening sequences that occur within the boundaries of eukaryotic genes.
35
Exons
- remaining coding regions that are expressed in proteins synthesis.
36
RNA splicing
- Removal of introns and joining of exons after a primary transcript is made of a gene
- occurs before the mRNA leaves the nucleus.
37
Alternative RNA splicing
- a type of eukaryotic gene regulation at the RNA-processing level
- different mRNA molecules are produced from the same primary transcript depending on which RNA segments are treated as exons and which as introns.
38
Relationship between number of genes and number of proteins
An organism can produce a greater number of proteins than the number of its genes
39
Spliceosome
small RNAs which form a large complex made of proteins that removes introns.
40
Ribozymes
RNA molecules that function as enzymes.
41
Transfer RNA (tRNA)
- molecules that carry amino acids to ribosomes where they are added to a growing polypeptide.
- each carries a specific amino acid
- each has an anticodon that base-pairs to its complementary mRNA codon
42
Functions of tRNA
- Aminoacyl-tRNA matches tRNA to amino acid
- match is made between the tRNA anticodon and mRNA codon
43
Anticodon
the particular nucleotide triplet attached to each tRNA that pairs to a specific mRNA codon.
44
Aminoacyl-tRNA synthetase
a family of enzymes that carry out the correct matching up of tRNA and amino acid.
45
Wobble
- flexible pairing that enables the third nucleotide base of some tRNA anticodons to pair with more than one codon.
46
Ribosomal RNA (rRNA)
- Makes up ribosomes
- Responsible for protein synthesis
47
3 Ribosome binding sites:
A, P and E sites
48
P site
holds the tRNA carrying the growing polypeptide chain.
49
A site
holds the tRNA carrying the next amino acid to be added the the chain.
50
E site
the exit site, where discharged tRNAs leave the ribosome.
51
Signal peptide
a sequence of about 20 amino acids at or near the leading end of the polypeptide
52
Signal-recognition particle (SRP)
particle that functions as an escort that brings the ribosome to a receptor protein built into the ER membrane.
53
Mutations
changes in the genetic information of a cell.
54
Point mutations
a mutation in a single nucleotide pair of a gene.
55
Nucleotide-pair substitution
the replacement of one nucleotide and its partner with another pair of nucleotides.
56
Silent mutations
a mutation that has no observable effect on the phenotype.
57
Missense mutation
a nucleotide-pair substitution that results in a codon that codes for a different amino acid.
58
Nonsense mutation
- when a point mutation changes an amino acid codon into a stop codon prematurely halting the translation of the polypeptide chain and usually creating a nonfunctional protein.
59
Insertions and deletions
are additions or losses of nucleotide pairs in a gene.
60
Frameshift mutations
a mutation that will occur whenever the number of nucleotides inserted or deleted is not a multiple of three. It creates extensive missense and nonsense mutations.
61
Mutagens
a number of physical and chemical agents that interact with DNA in ways that cause mutations.
62
What do alterations to the shape or number of chromosomes cause?
Genetic disorders such as spontaneous abortion (miscarriage) or developmental disorders
63
What are the nucleotide base pairs
- adenine and thymine (DNA) or Uracil (RNA)
- cytosine and guanine
64
How many amino acids are there?
20
65
Number of triplets and the 2 things they code for:
64 triplets
- 61 code for amino acids
- 3 code for "stop" to end translation
66
What is meant by, "the genetic code is redundant but not ambiguous"?
- redundant: an amino acid can be specified by more than one codon
- not ambiguous: each codon only specifies one amino acid
