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Introduction to Genetics & Biochemistry > The Genetic Code & Transcription > Flashcards

The Genetic Code & Transcription Flashcards

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1
Q

Who proposed the central dogma of molecular genetics and what is it?

A

Francis Crick proposed that genetic information moves in one direction only.

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2
Q

How many nucelotides form a codon?

A

Three.

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3
Q

True or false? It doesn’t matter what order the nucleotides are in in a codon.

A

False. The order of nucleotides in a codon is critical!

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4
Q

Each codon codes for a specific…..?

A

Amino acid.

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5
Q

How many codons are there? Given that there are twenty amino acids, whatr does this mean?

A

There are sixty-four codons in total. Some codons have other functions and some do not code for an amino acid at all.

Most amino acids are specified by more than one codon.

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6
Q

The codon ATG codes for methionine, but it also acts as a ……………… signal?

A

ATG acts as a start signal to intiate the process of transcription.

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7
Q

What do the codons TAA, TGA and TAG have in common?

A

They are all nonsense codons. They do not code for an amino acid, instead they act as a stop signal for transcription.

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8
Q

What is ‘third base wobble’?

A

‘Third base wobble’ is when the third nucleotide in a codon is redundant, e.g. ACT, ACC, ACA and ACG all code for threonine.

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9
Q

What is a reading frame?

A

The reading frame is a set of three codons, set off by the ATG start codon.

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10
Q

What happens if a reading frame mutation happens?

A

A mutation of the wrong reading frame can be really severe compared to a single base change as it can alter the whole sequence completely.

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11
Q

How can the insertion of one nucleotide affect the reading frame?

A

The insertion of one nucelotide in the ‘wrong’ place can shift the whole reading frame, often with drastic consequences!

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12
Q

How do we know that the universal genetic code must have developed early on in the evolution of life?

A

(Almost) all genes in eukaryotes and bacteria share the same genetic code.

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13
Q

Name an exception in the universal genetic code.

A

Mitochondria have their own chromosomes and synthesise their own proteins. They are thought to have originally been a bacterium that became symbiotic during the evolution of the first eukaryotic cells.

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14
Q

Why does the genetic code need to be ‘punctuated’ by start and stop signals?

A

To set the reading frame. Without clear signals to start and stop transcription, there are multiple possible reading frames.

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15
Q

If every cell in humans is genetically identical, why are they morphologically different?

A

Although every cell contains the same genetic information, different genes are expressed (switched on or off) depending on the intended function of the cell. This determines the proteins that the cell makes.

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16
Q

What is gene regulation?

A

The ability of a cell to control the regulation of each gene.

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17
Q

Name three factors that can affect gene expression.

A
  1. Transcription rate.
  2. Translation.
  3. mRNA storage.
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18
Q

Proteins cannot be modified after they have been made. True or false?

A

False.

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19
Q

In eukaryotes, there is an extra step where …………… is processed into ………….. and gene expression can be controlled by deciding whether to allow ……………. out into the …………….. .

A

Pre-mRNA, mRNA, mRNA, cytoplasm.

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20
Q

Is this RNA polymerase 1, 2, or 3?

Transcribes most ribosomal RNA (rRNA).

A

RNA polymerase 1.

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21
Q

Is this RNA polymerase 1, 2, or 3?

Transcribes messenger RNA (mRNA).

A

RNA polymerase 2.

22
Q

Is this RNA polymerase 1, 2, or 3?

Transcribes transfer RNA (tRNA) and one small ribosomal RNA (rRNA).

A

RNA polymerase 3.

23
Q

RNA polymerases are large, complex ……………. made up of about ten …………….. .

A

Enzymes, proteins.

24
Q

True or false? The structure of the genes transcribed by each type of RNA polymerase differs, as does the process of expression?

A

True.

25
Q

The genes transcribed by which RNA polymerase are the most important in distinguishing one cell from another?

A

RNA polymerase 2.

26
Q

True or false? Prokaryotes have different RNA polymerases which synthesise different RNA?

A

False. In prokaryotes the same RNA polymerase synthesises both mRNA and non-coding RNA.

27
Q

What is the main difference between the promoter in prokaryotes and eukaryotes?

A

Prokaryotes - RNA synthesis always starts at the same point on the DNA. This point is a ‘promoter’ and the RNA polymerase binds directly to it.

Eukaryotes - In eukaryotes, several transcription factors (proteins) must bind to the promoter, the RNA polymerase then binds to these transcription factors.

28
Q

At what three points can the the expression of prokaryotic genes be controlled?

How does this differ from eukaryotic gene expression?

A

Transcription, translation and post-translation.

Eukaryotic gene expression has an extra level of control where RNA is processed post-transcription.

29
Q

At which four points can eukaryotic gene processing be controlled?

How does this differ from prokayotic gene expression?

A

Transcription, RNA processing, translation and post-translation.

Prokaryotic gene expression does not have the RNA processing step.

30
Q

Which step in the gene expression can be described as:

‘The process where DNA is copied into RNA using RNA polymerase’?

A

Transcription - the first step.

31
Q

When DNA is being transcribed, the mRNA mRNA has the same codons as the coding strand - but with one of the nucleotides replaced. Which one? What replaces it?

A

Thymine in DNA is replaced by uracil in mRNA.

32
Q

Is RNA growth in the 5’ to 3’ direction or the 3’ to 5’ direction?

A

RNA growth is always in the 5’ to 3’ direction.

33
Q

Genes are always copied from one strand of DNA - what is this strand called?

A

The coding strand.

34
Q

True or false? The coding strands of different genes are always on the same strand of a chromosome?

A

False. The coding strands of different genes can be on different strands of a chromosome.

35
Q

What are introns and exons?

A

Introns are non-coding sequences of DNA which interrupt the coding exons. They exons have to be spliced together to create an uninterrupted sequence.

36
Q

Describe the process of splicing.

A

Splicing occurs when coding exons are interrupted by non-coding sequences of introns. These introns are cut out and the exons spliced together to create a uninterrupted sequence.

37
Q

Where are the poly a tail and 5’ cap added to the mature mRNA transcript?

A

In the nucleus.

38
Q

The poly A tail added to mature mRNA is not present in DNA - what is it amd where does it come from?

A

It is a repeated sequence of adenine nucleotides which are added by an enzyme.

39
Q

In E.Coli, ……………….. proteins are made from a ……………. strand of mRNA.

A

Multiple, single.

40
Q

What is located from -300 to +1 of the coding strand of eukaryotic DNA?

A

The promoter region.

41
Q

The core promoter of eukaryotic DNA is located from -25 to +1 of the coding DNA strand. It is made of which two conserved sequences, which are always present?

A

The TATA box and the transcriptional startr site (+1).

42
Q

What is commonly located at -300 to -50 of the coding strand of DNA?

A

Regulatory elements, which can influence a gene being turned on and off.

43
Q

True or false? Transcription elongation is very similar in prokaryotes and eukaryotes.

A

True. During transcription elongation the DNA double helix rewinds after transcription.

44
Q

Prokaryotic transcription termination can be …….. -independent or ………….. -dependent.

A

Rho.

45
Q

What process does the following describe? Does it occur in prokaryotes or eukaryotes?

Transcription stops when RNA forms a hairpin loop followed by a uracil poly-tail.

A

This is prokaryotic rho-independent transcription termination.

46
Q

What is being described here? Does it occur in prokaryotes or eukaryotes?

A protein termination factor interacts with the elongating RNA transcript and disrupts the interaction between the DNA template and RNA transcript.

A

Prokaryotic rho-dependent transcription termination.

47
Q

Is transcription termination in eukaryotic DNA fully understood?

A

No.

48
Q

What do we know about eukaryotic transcription termination?

A

The RNA transcripts are cleaved by specific endonucleases and a poly (A) tail is added by polymerase.

49
Q

Where in the cell does transcription and translation take place in prokaryotes?

A

In the cytosol.

50
Q

Where in the cell does eukaryotic transcription and translation take place?

A

Transcription (and RNA editing) - in the nucleus.

Translation - in the cytosol.

Introduction to Genetics & Biochemistry (9 decks)

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