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gene expression Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is a gene?

A

A gene is a discrete unit of hereditary information that consists of specific nucleotide sequence in DNA

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2
Q

If 2 nucleotides code for 1 amino acid, how many types of amino acids does it contain?

A

4^2=16, insufficient to code for 20 different amino acids

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3
Q

What is the smallest unit of nucleotides needed to sufficiently code for all 20 amino acids?

A

3

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4
Q

Name the 5 features of the genetic code.

A

It is a triplet code, it is degenerate, it is punctuated, it is non-overlapping and it is universal.

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5
Q

More than one mRNA codon code for the same amino acid. True/False.

A

True. The first two of the three nucleotides in the codon are usually the same. (Degenerate)

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6
Q

Each triplet is transcribed into one mRNA codon. True/False.

A

True. DNA triplet code is transcribed into mRNA before protein is made. mRNA codons are complementary to DNA triplets on the template strand. (Triplet code)

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7
Q

There are only stop codons for the start and end of translation. True/False.

A

False. There are start and stop codons for start and end of translation. The presence of start codon AUG signals start of translation of mRNA into amino acids. The stop codons UAA, UGA, UAG act as stop signals for termination of polypeptide chain during translation. (Punctuated)

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8
Q

The stop codon codes for amino acids. True/False.

A

False. The stop codon does not code for any amino acid. (Punctuated)

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9
Q

What does it mean by the genetic code is non-overlapping?

A

The reading frame for each triplet is fixed and the codons do not overlap. (Non-overlapping)

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10
Q

The genetic coded is used in all organisms. True/False/

A

True. (Universal)

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11
Q

What is transcription?

A

It is the synthesis of RNA using the DNA template strand.

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12
Q

Where does transcription take place?

A

It takes place in the nucleus of eukaryotic cells and cytoplasm of prokaryotes.

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13
Q

What is a promoter?

A

It is a region of DNA upstream, where RNA polymerase and transcription factors attach to and initiate transcription.

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14
Q

In eukaryotes, there is a DNA sequence within the promoter called the…

A

TATA box. It is recognised by transcription factors and RNA polymerase. It is rich in Adenine and Thymine. (Eukaryotes)

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15
Q

In prokaryotes, the DNA sequence within the promotor is recognised by…

A

Only RNA polymerase known as the Pribnow box.

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16
Q

What is the RNA-Coding region?

A

It is the region of DNA that is transcribed into an RNA molecule.

17
Q

Are there coding and non coding regions within transcription unit in eukaryotes and prokaryotes?

A

Eukaryotes - There are coding (exons) and non-coding regions (introns) within the transcription unit.
Prokaryotes - There are only coding regions.

18
Q

What is the terminator?

A

It is the sequence of DNA downstream of the transcription start site that signals the end of transcription.

19
Q

How does transcription initiation occur in eukaryotes?

A

First, the transcription factors recognise and attach to the TATA box in the promoter.

The bound transcription factors facilitate the binding of RNA polymerase to the promoter.

A transcription initiation complex is formed.

RNA polymerase undergoes conformational change and this allows it to be bound in the correct orientation.

The RNA polymerase will unwind and unzip the DNA molecule and starts transcribing the template strand.

20
Q

How does transcription initiation occur in prokaryotes?

A

Only RNA polymerase recognises and binds to the Pribnow Box in the promotor to initiate transcription.

21
Q

How does elongation occur in both eukaryotes and prokaryotes?

A

RNA polymerase moves along the DNA template strand in the 3’ to 5’ direction. It takes up the free ribonucleotides by complementary base pairing.

RNA polymerase catalyses the formation of phosphodiester bonds between adjacent ribonucleotides.

mRNA is synthesised in the 5’ to 3’ direction due to antiparallel nature.

22
Q

Why does RNA polymerase not need primer unlike DNA polymerase?

A

It does not require an existing free 3’OH group to add ribonucleotides.

23
Q

How does termination occur in eukaryotes?

A

Occurs within a terminator region with no well defined sequence.

Transcription is terminated only after RNA polymerase transcribes the DNA sequence which codes for a polyadenylation signal.

Takes about 10-35 nucleotides downstream.

Proteins will cause RNA polymerase to detach from the DNA, releasing the RNA strand.

24
Q

What is the product of transcription called?

A

RNA transcript.

25
Q

Describe the function of 5’UTR and 3’UTR.

A

5’UTR: facilitates binding of small ribosomal subunit on mRNA, increasing translational efficiency.

3’UTR: maintain stability of mRNA.

26
Q

How does termination occur in prokaryotes?

A

RNA polymerase transcribes a terminator sequence. It functions as a termination signal, causing RNA polymerase to detach from DNA and release the RNA strand.
Does not contain introns.

27
Q

Post transcriptional modification occurs in both eukaryotes and prokaryotes. True/False.

A

False. It only occurs in eukaryotes after transcription and before translation.

28
Q

Outline what happens during post transcriptional modification.

A

After transcription occurs in the nucleus, mRNA needs to be transported out through nuclear pore for translation to occur in the cytoplasm.

To allow transport of mRNA and regulation of gene expression, PTM must first occur in the nucleus. Pre-mRNA undergoes 3 PTMs.

  1. Addition of 5’ modified GTP Cap
    - Modified guanosine triphosphate is added to the 5’ end of the pre-mRNA.
  2. RNA splicing
  3. Addition of 3’ Poly (A) Tail
29
Q

What is an mRNA molecule that has no completed and completed post transcriptional modification respectively?

A

Not completed - pre mRNA.

Completed - mature mRNA.

30
Q

Name 3 functions of addition the 5’ GTP Cap.

A
  1. Facilitates the export of mature mRNA
  2. Prevents degeneration of mRNA
  3. Helps ribosome attach to the 5’ end during translation

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