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A Level Biology > Chapter 3 - Nucleotides > Flashcards

Chapter 3 - Nucleotides Flashcards

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1
Q

double ringed structures?

A

PURINES

Guanine, Adenie

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2
Q

single ringed structures?

A

pYrimidines
thYmine
cYtosine
Uracil

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3
Q

2 reasons why base pairing is so specific?

A

1- Purines pair with pyrimidines
2- G: C base pairs have 3H bonds
- A:T base pairs have 2H bonds

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4
Q

base pairing memory trick?

A

C is the third letter of alphabet

TA2 - Tattoo

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5
Q

the 2 DNA strands are _____ and form a ____ ______ molecule. this is ___ ______

A

anti parallel, double helix

right handed

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6
Q

function of DNA?

A
  1. allows cells to divide, bc it can replicate

2. contains the genetic code - instructions for protei synthesis

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7
Q

Extracting DNA from plant cells - chop/ grind/ liquidise

A
  • breaks down cell walls allowing DNA to exit the cellss
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8
Q

Extracting DNA from plant cells -place in water bath @60 for 5 mins

A
  • when cells are damaged, enzymes are released which easily break down DNA
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9
Q

Extracting DNA from plant cells - filter the blended mixture

A

broken down cells contain a mixture of organelles and cell fragments

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10
Q

Extracting DNA from plant cells - detergent

A

DNA is in the nucleus, behind the plasma membrane and the nuclear envelope

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11
Q

Extracting DNA from plant cells -addition of protease enzymes

A

DNA is closely associated with histone proteins

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12
Q

Extracting DNA from plant cells -add ice cold ethanol

A

DNA is soluble in water so you can’t see it in solution

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13
Q

what did meselson and stahl do?

A
  • grew e-coli cells in Nitrogen 15 medium for many generations
  • analyse DNA with density gradient centrifugation
  • Then put sample of E-coli in Nitrogen 14 medium for 1 generation
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14
Q

what is semi conservative DNA replication?

A
  • DNA molecule separates into 2 strands
  • Each old strand is used as a template
  • Free nucleotides are added to each strand using rules of complementary base pairing
  • 2 molecules of DNA are formed, each consisting of 1 new strand and 1 old
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15
Q

DNA replication problem?

A

free nucleotides can be only be added to the 3’ and not 5’ end

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16
Q

what does DNA ligase do?

A

forms phosphodiester bonds between Okazaki fragments completing the strand

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17
Q

Replication bubbles?

A

DNA replicates from multiple origins of replication forming replication bubbles

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18
Q

the genetic code - universal

A

the fact that all life shares a universal genetic code is one of the most powerful pieces of evidence that life has evolved from a common ancestor

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19
Q

the genetic code - triplet code

A
  • 20 amino acids which all proteins are made from

- triplet code - 64 AAs can be coded for - more than enough (4x4x4 = 64)

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20
Q

the genetic code - degeneracy

A

some AAs have more than one triplet coding for them. This gives the genetic code some capacity for absorbing mutations without any effect
- also gives for stop triplets - 3 of these

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21
Q

the genetic code - non - overlapping

A
  • a gene always starts with the same triplet - called the start codon. this ensures that the code is always read ‘in frame’
22
Q

the start codon…

A

sets the reading frame and ensures that triplets do not overlap

23
Q

which strand is read in transcription?

A

DNA has 2 strands - antisense & sense. The antisense stand is read by RNA polymerase in the process of transcription to form RNA

24
Q

Protein synthesis?

A

how a specific sequence of bases in DNA is converted to a specific sequence of AAs in a protein

25
Q

2 processes in protein synthesis?

A
  1. Transcription: DNA -> mRNA

2. Translation; mRNA -> protein

26
Q

tRNA?

A

tRNA transfers specific amino acids from the cytoplasm to the ribosome during translation
- the codon anticodon base pairing determines which specific AAs is transferred

27
Q

what is a gene?

A

A section of DNA that contains the complete sequence of bases (codons) to code for an entire protein

28
Q

What is rRNA important for?

A
  • maintaining structural stability of the protein synthesis sequence
  • plays a biochemical role in catalysing the reaction
29
Q

What is a nucleotide?

A

a molecule composed of a pentose sugar, phosphate group, nitrogenous base. it is the monomer unit of nucleic acids

30
Q

what is a polynucleotide?

A

a polymer made up of many nucleotide monomers joined together by a series of condensation reactions

31
Q

What did Watson & Crick discover?

A

DNA was composed of 2 very long polynucleotide chains twisted into a double helix

32
Q

the double helix of DNA is …

A

anti parallel meaning the strands of DNA run in opp directions to each other

33
Q

RNA is ___ stranded and shorter than ___

A

single, DNA

34
Q

DNA rep takes place during which stage of cell cycle?

A

inter-phase, phase before cell begins to /

35
Q

key:

A
  • synthesis happens from 5’ to 3’

- new nucleotide added to 3’

36
Q

DNA helicase ?

A

Is an enzyme that catalyses the breaking of H bonds between the complementary organic bases in DNA

37
Q

DNA polymerase?

A

the enzyme that catalyses the formation of phosphodiester bonds and the adjoining od adjacent new nucleotide

38
Q

Semi conservative replication definition?

A

the method in which DNA replicates creating 2 molecules of DNA that consist of 1 original DNA strand and one newly synthesised DNA strand

39
Q

leading strand

A
  • RNA polymerase can only add new nucleotides in 3’ to 5’ direction
  • allows one strand to be synthesised continuously
40
Q

lagging strand?

A

synthesis of other strand is discontinuous as DNA polymerase moves away from the strand

41
Q

Okazaki fragments?

A

lagging strand is synthesised in short sections called Okazaki fragments

42
Q

What is functional RNA?

A

The RNA that has a functional role in an organism other than coding for proteins

43
Q

Transcription def?

A

the process of making messenger RNA from a DNA template

44
Q

Translation def?

A

The process of making proteins by forming a specific sequence of amino acids based on coded instructions in the mRNA

45
Q

what is the genetic code?

A

the specific sequence of bases in DNA or RNA that codes for a sequence of AAs during protei synthesis

46
Q

codon definition?

A

a codon is a specific sequence of 3 bases of RNA and DNA that code for a specific amino acid

47
Q

3 stop codons are:

A

TAG, TAA, TGA

- do not code for any AAs, causing translation to cease

48
Q

why does tRNA have a clover leaf shape?

A

bc it can form complementary base paris with itself

49
Q

what does the degeneracy of the genetic code mean for tRNA?

A

tRNAs with diff anticodons can bind to the same amino acid

50
Q

what is a ribozyme?

A
  • The RNA that exists in the large subunit is called a catalyse which catalyses the formation of peptide bonds as polypeptides are formed
  • as this catalyst is an RNA molecule, not protein, it’s called a ribozyme instead of enzyme
51
Q

How does translation end ?

A
  • no tRNA molecules with complementary anti-codons for the stop codons
  • so when stop codon is reached, no tRNAs can bind and the synthesised polypeptide is released from the last tRNA molecule
52
Q

what is a sense strand?

A

the only one out of the 2 strands that contains the codons that are used to code for AAs

A Level Biology (28 decks)

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