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Genetics And Evolution > Transcription, Splicing, Translation > Flashcards

Transcription, Splicing, Translation Flashcards

1
Q

Where does transcription take place in eukaryotes?

A

Nucleus

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2
Q

Where does transcription take place in prokaryotes?

A

Cytoplasm

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3
Q

Where does translation take place in eukaryotes?

A

Cytoplasm

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4
Q

Where does translation take place in prokaryotes?

A

Cytoplasm

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5
Q

What is transcription?

A

Gene expression- using the gene as a template to synthesise RNA

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6
Q

What is translation?

A

Using RNA as a template to synthesise a protein

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7
Q

What are the 3 essential components of transcription?

A

Protein coding gene

RNA polymerase

NTPs (Nucleoside Triphosphates)

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8
Q

What are the 3 stages of transcription?

A

Initiation
Elongation
Termination

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9
Q

What is a promotor?

A

Specific DNA sequence, starts transcription

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10
Q

What is a terminator?

A

Specific DNA sequence, determines end of RNA transcript

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11
Q

What bacterial RNA polymerase structure?

A

Five polypeptides (protein subunits)
Alpha (2 copies), beta, beta and sigma (halo enzyme)
Sigma subunit can dissociate. (Core enzyme)

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12
Q

What part of RNA polymerase binds to DNA?

A

Sigma subunit

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13
Q

What is a nucleoside?

A

Base attached to the ribose sugar

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14
Q

What are the 4 NTPs for the 4 bases?

A

Uridine triphosphate for uracil

Cytidine triphosphate for Cytosine

Adenosine triphosphate for adenine

Guanosine triphosphate for guanine

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15
Q

What happens in initiation of transcription?

A

Occurs at promoter

RNA polymerase binds to promoter and begins to unwind the DNA

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16
Q

What happens in elongation of transcription?

A

RNA polymerase moves along the DNA template

RNA strand grows by addition of NTPs to its 3’ end in the unwound region

As DNA + RNA transcripts exits, RNA polymerase is removed from the DNA template, and DNA rewinds

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17
Q

What happens in termination of transcription?

A

When RNA polymerase reaches termination site, RNA transcript is released from template

RNA polymerase dissociates from DNA and can perform other rounds of transcription

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18
Q

What are the similarities between replication and transcription?

A

General steps involve initiation, elongation and termination (from 5’ to 3’ end)

Both involve enzymes that synthesise a new nucleic acid strand complemtary to DNA template

Large multicomponent initiation complexes

Adhere to Watson-Crick base pairing rules

Both of them are highly regulated

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19
Q

What are the differences between replication and transcription?

A

Only a portion of the genome is transcribed to RNA in transcription, whereas the entire genome must be replicated for DNA replication

Transcription copies one strand of DNA making one mRNA strand but replication copies both strands of DNA making two new semi conservative DNA strands

Ribonucleotides are used in transcription, whereas deoxyribonucleotides are used in replication

U replaces T as a complementary base for A in transcription

No primer involved in transcription

RNA polymerase used in transcription, DNA polymerase used in replication

No proof reading in transcription, whereas there is in replication

End product: DNA has twi strands whilst RNA has one

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20
Q

What are important components for initiation of eukaryotic transcription?

A

TATA box- DNA sequence within the promoter region of DNA

Transcription factors- Proteins that bind to DNA and influence transcription

RNA polymerase (with sigma sub unit)

21
Q

How far upstream is the TATA box from the transcriptional start point?

A

Approx 25 nucleotides upstream

22
Q

What do the transcription factors in transcription do?

A

One TF recognises the TATA box and binds

Additional TFs recognise the bound TF and bind

RNA polymerase recognises the TFs, enabling it to bind to DNA in the correct position and orientation

Additional TFs bind to DNA with RNA polymerase. Makes a transcription initiation complex

RNA polymerase unwinds the DNA double helix, and RNA synthesis begins at the start codom on template strand

23
Q

What are the important components for termination of eukaryotic transcription?

A

Polyadenylation signal sequence- DNA sequence within the termination site region of DNA. Codes for polyadenylation signal in mRNA

Enzyme- recognises polyadenylation signal and releases mRNA from RNA polymerase

25
What are the additions to mRNA ends?
5' cap: -Added during transcription while mRNA is still being transcribed. -It's a chemically modified molecule of GTP ( guanosine triphosphate) -It facilitates binding of mRNA to an enzyme (ribosome) for translation AND protects mRNA from being digested by ribonucleases 3' tail: -Added immediately after mRNA transcript has been released from RNA polymerase -It's a poly A tail, 100-300 adenine nucleotides -Exports mRNA from nucleus to cytoplasm -Stabilises mRNA
26
What is an intron and which cells have them?
Non coding sequence of DNA Eukaryotes have them
27
What process removes introns and what molecules do this?
Splicing Done by Small nuclear ribonucleoproteins (snRNPs)
28
What happens in splicing?
snRNPs bind to consensus sequences near the 5' and 3' splice sites Other snRNPs also attach at additional points along the pre-mRNA snRNPs join together to form a spliceosome Intron loops out Spliceosome cuts pre-mRNA at 5' intron/exon boundary The free 3' OH group at the end of the cut exon reacts with the 5' phosphate group of another exon 3' exon cleaved and splices to 5' exon, makes mature mRNA Intron degraded into the nucleus
29
What are the two steps of RNA processing?
Additions to pre-mRNA ends Removal of introns
30
Is transcription the control point of gene expression?
The amount of transcription determines how much protein is made
31
32
What are the important components of translation?
mRNA tRNA- links information in mRNA codons with specific amino acids in protein Amino acids Ribosomes- catalyzes the formation of peptide bonds between amino acids
33
What is a codon?
Series of 3 nucleotides in mRNA that codes for an amino acid
34
What is the start codon?
AUG
35
What are the 3 stop codons?
UAA UAG UGA
36
What are the 3 stages of translation?
Initiation Elongation Termination
37
What happens in initiation of translation?
Ribosome small subunit attaches to mRNA Ribosome small subunit moves along the mRNA until it reaches the start codon. AUG is always the start codon Methione charges tRNA containing complementary sequence to start codon binds to the start codon. Fiesta amino acid in the polypeptide chain is methionine. The combination of mRNA, ribosome small sub unit and tRNA forms the initiation complex Ribsome large sub unit joins the initiation complex. The large sub unit has 3 specific sites- A (anticodon), P (polypeptide), E (exit) Methionine charges tRNA occupies the P site The A site is aligned with next mRNA codon
38
What happens in elongation of translation?
Anticodon of an incoming tRNA binds to the codon at the A site of the ribosome Proline is linked to Methionine by peptidyl transferase activity of the ribosome large sub unit Peptidyl transferase undergoes 2 reactions- 1.break home between amino acid and its tRNA in P site. 2. form bond between that amino acid and the amino acid attached to its tRNA in A site Free tRNA is moved to E site and releases as the ribosome moves along to the next codon Growing polypeptide chain moves to the P site
39
What happens in termination of translation?
A release factor binds to the complex when a stop codon enters the A site Release factor disconnects the polypeptide from the tRNA in the P site Remaining components separate
40
What happens after translation?
Information in the amino acid sequence gives it one of two possible sets of further instructions: 1. Stay within the cell- Complete translation and be released to an organelle or remain in the cytosol 2. Stop translation, go to the endoplasmic reticulum and finish synthesis there before transport out the cell
41
How are polypeptide chains modified?
Proteolysis Glycosylation Phosphorylation
42
What is proteolysis?
Cutting the polypeptide allowing the fragments to fold into different shapes
43
What is glycosylation?
Addition of sugars to polypeptide, important for targeting and recognition Forms glycoproteins Catalysed by enzymes in the ER and golgi apparatus
44
What is phosphorylation?
Addition of phosphate groups, alter the shape of the protein Catalysed by protein kinases Charged phosphate groups change the confirmation of a protein Important for cell signalling
45
When can regulation of gene expression happen?
Before transcription During transcription After transcription, but before translation During translation After translation
46
What two regulatory proteins are involved in regulation of gene expression?
Repressor proteins- negative regulation Activator proteins- positive regulation
47
What is negative regulation?
Binding of repressor protein blocks transcription (stops RNA polymerase from binding to promoter)
48
What is positive regulation?
Binding of activator protein stimulates transcription (allows RNA polymerase to bind to the promoter)

Genetics And Evolution (10 decks)

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