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Biology > Topic 7 > Flashcards

Topic 7 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are the purines?

A

Guanine & Adenine -> they contain 2 rings in their structure

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2
Q

What are the pyrimidines?

A

T & C -> they contain 1 ring in their structure

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3
Q

What are the enzymes involved in DNA replication?

A
  • DNA gyrase
  • DNA helicase
  • DNA polymerase (III)
  • DNA polymerase (I)
  • DNA ligase
  • DNA primase
  • SSB proteins(not an enzyme but important)
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4
Q

The regions of DNA that do not code for any proteins are what?

A
  • introns
  • telomeres
  • genes for tRNA’s
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5
Q

What are tandem repeats?

A

sequences of non-coding DNA, normally the length of 2-5 base pairs, that are repeated numerous times in a head-tail manner

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6
Q

Lagging strand

A

the strand of DNA that is replicated discontinuity in small fragments in the 5’3’ direction away from the replication fork

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7
Q

Leading strand

A

the strand of DNA that is being replicated continuously in the 5’3’ direction by continuous polymerisation at the 3’ growing tip

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8
Q

Enhancers

A

sequences that increase the rate of transcription (when a protein is bound to it)

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9
Q

Silencers

A

sequences that inhibit transcription (when a protein is bound to it)

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10
Q

Promoter

A

a promoter is a short DNA sequence situated just before a gene, which acts as a binding point for the RNA polymerase enzyme

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11
Q

Operator

A

a region of DNA that can regulate transcription, typically inhibiting the transcription gene

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12
Q

Methylation

A

the addition of methyl groups to DNA

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13
Q

what is the effect of methylation?

A

DNA is more tightly bound to the histone which makes the DNA less accessible to transcription factors -> can inhibit transcription

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14
Q

Acetylation

A

addition of acetyl groups to histones

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15
Q

what is the effect of acetylation?

A

causes the DNA to bind less tightly to the histones

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16
Q

Events that occur to form mature mRNA

A
  • capping
  • polyadenylation
  • splicing
17
Q

Capping

A
  • involves the addition of a methyl group to the 5’-end of the transcribed RNA
  • the methylated cap provides protection against degradation by exonucleases
  • allows the transcript to be recognised by the cells transitional machinery
18
Q

Polyadenylation

A
  • describes the addition of a ling chain of adenine nucleotides to the 3’-end of the transcript
  • the poly-A tail improves the stability of the RNA transcript and facilitates its export from the nucleus
19
Q

Splicing

A
  • can happen in different ways to the same gene

- introns are removed & the non-coding exons are fused together to form a continuous sequence

20
Q

Alternative splicing

A
  • the removal of extrons
  • The selective removal of specific exons will result in the formation of different polypeptides from a single gene sequence
21
Q

translation occurs in 3 distinct stages:

A
  • initiation
  • elongation
  • termination
22
Q

Initiation

A

involves the assembly of the components that carry out the process

23
Q

What happens in initiation/

A
  • small ribosomal unit binds to the 5’-end of the mRNA & moves along until it reaches the start start codon (AUG)
  • next, the appropriate tRNA molecule binds to the codon via its anticodon (according to complementary base pairing)
  • finally, the large ribosomal subunit aligns itself to the tRNA molecule at the P site & forms a complex w the small subunit
24
Q

What happens in Elongation

A
  • a second tRNA molecule pairs w the next codon in the ribosomal A site
  • the amino acid in the P site is covalently attached via a peptide bond (condensation reaction) to the amino acid in the A site
  • the tRNA in the P site is not deacylated (no amino acid), while the tRNA in site A carries the peptide chain
  • the ribosome moves along the the mRNA strand by 1 codon position (in a 5’→3’ direction)
  • the deacylated tRNA moves into the E site & is then released, while the tRNA carrying the peptide chain moves to the P site
  • another tRNA molecule is attached to the next codon in the now occupied A site, & the process is then repeated
25
Q

Termination

A

involves the disassembly of the components

26
Q

What happens in termination?

A
  • elongation continues until in a repeating cycle until the ribosome reaches the codon stop
  • These codons do not recruit a tRNA molecule, but instead recruit a release factor that signals for translation to stop
  • The polypeptide is released and the ribosome disassembles back into its two independent subunits
  • All of these components can be reused for another translation complex.
27
Q

Why translation can occur immediately after transcription in prokaryotes

A
  • due to absence of nuclear membrane
  • In prokaryotes ribosomes can be adjacent to the chromosomes, whereas in eukaryotes the mRNA needs to be relocated from the nucleus to the cytoplasm (through the nuclear membrane)
  • mRNA is not modified(spliced) in prokaryotes
28
Q

What is a polysome/polyribosome?

A

is a structure that consists of multiple ribosomes attached to a single mRNA

29
Q

What is protein destination determined by?

A

he presence or absence of an initial signal sequence on a nascent polypeptide chain

30
Q

DNA helicase

A
  • unwinds and separates DNA strands by breaking the hydrogen bonds between base pairs
  • occurs at specific regions (origins of replication)
31
Q

DNA gyrase

A
  • moves in advance of DNA helicase & relieves torsional strain created by the unwinding of DNA
  • relaxes the positive supercoils via neg supercoiling that would otherwise form
32
Q

DNA ligase

A

joins the Okazaki fragments together to form a continuous strand
- covalently joins the sugar-phosphate backbones together w a phosphodiester bond

33
Q

DNA polymerase I

A

lagging strand is synthesised in a series of Okazaki fragments- thus multiple RNA primers along its length
-DNA pol I removes the RNA primers, replacing them w DNA nucleotides

34
Q

RNA primase

A
  • generates a short RNA primer on the template strands

- provides an initiation point for DNA polymerase III, which can extend a nucleotide chain but not start one

35
Q

SSB

A

bind to the DNA strands after separation - prevent strands from re-annealing

  • prevent the single stranded DNA from being digested by nucleases
  • they are dislodged form the strand when a new complementary strand is synthesised
36
Q

What is X-ray diffraction?

A

when x-ray is directed at a material, some of it is scattered by that material

37
Q

What supports complementary base pairing?

A
  • X-ray diffraction
  • the electrical charges of adenine & thymine are compatible allowing the hydrogen bonds to form between them
  • pairing of C w G allows for 3 hydro bonds to form between them
38
Q

How does X-ray diffraction support complementary base pairing?

A

it showed that the DNA helix is both tightly packaged & regular, therefore pyramids need to be paired w purines

Biology (28 decks)

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