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OCR A level Biology > 2.1.3 - Nucleotides and Nucleic Acids > Flashcards

2.1.3 - Nucleotides and Nucleic Acids Flashcards

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1
Q

What is a nucleotide made of

A

Pentose monosaccharide
Phosphate Group PO4 2-
Nitrogenous base

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2
Q

Phosphodiester bonds

A

Formed in a condensation reaction between nucleotides
Phosphate group at 5’ forms covalent bond with hydroxyl group 3’ (H2O)
Forms a long, strong sugar-phosphate backbone with a base attached to each sugar

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3
Q

Difference between ribose and deoxyribose

A

Deoxyribose doesn’t have an oxygen atom at 2’

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4
Q

Bases

A

Adenine
Cytosine
Guanine
Thymine/ uracil

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5
Q

Pyrimidines

A

Smaller bases
Single carbon ring structures
Thymine/ Cytosine

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6
Q

Purine

A

Larger bases
Double carbon ring structures
Adenine/ Guanine

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7
Q

How do bases pair up

A

A purine with a pyramidine
Cytosine pairs with guanine - 3 H bonds
Adenine pairs with thymine (uracil - RNA) - 2 H bonds

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8
Q

Structure of DNA

A

Hydrogen bonding between complementary bases
Double helix composed of two twisted antiparallel strands (phosphate group 5’ - OH 3’/ OH 3’ - phosphate group 5’)
Each strand is a polynucleotide

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9
Q

Why are polynucleotide chains parallel

A

Complementary base pairing rule:
When a small pyramidine base binds to a larger purine base a constant distance between the DNA ‘backbones’

There will also always be equal amounts of A, T, C, G

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10
Q

Types of RNA

A 
Messenger RNA (mRNA)
Transfer RNA (tRNA) 
Ribosomal RNA (rRNA)
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11
Q

mRNA

A

Carries the code held in the genes to the ribosomes where the code is used to manufacture proteins

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12
Q

tRNA

A

Transports amino acids to the ribosomes

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13
Q

rRNA

A

Makes up the ribosomes along w/ protein complexes

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14
Q

Phosophorylated nucleotides

A

ADP and ATP
Contain a pentose sugar (ribose)
A nitrogenous base (adenine)
2/ 3 inorganic phosphates

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15
Q

Semi conservative replication

A

One old strand and one new strand

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16
Q

Process of semi-conservation replication

A

Helicase causes the DNA to untwist and breaks the hydrogen bonds between bases
Polynucleotides with exposed bases act as new template for new double strands
Free DNA nucleotide bases pair with their complementary bases - H bonds
DNA polymerase catalyses the formation of phosphodiester bonds between the nucleotides and also checks base pairing
Sugar phosphate backbone reforms
Each new molecule then twists to form it’s double helix

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17
Q

Purpose of DNA replication

A

Genetic info needs to be conserved with accuracy so each cell from cell division has the correct amount of genes

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18
Q

Continuous replication

A

DNA polymerase binds to the end of a strand
Free DNA nucleotides added without any breaks
This occurs in the leading strand (3’ to 5’)

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19
Q

Discontinuous replication

A

DNA polymerase cannot bind to the end of a strand (5’- 3’)
Free DNA nucleotides are added in sections (Okazaki fragments)
Sections are later joined by DNA ligase

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20
Q

Mutations

A

Incorrect sequences may occur in the newly-copied strand
Errors happen randomly and spontaneously
Leads to change in the sequence of bases

21
Q

Codon

A

Triplet of bases that code for an amino acid

22
Q

Genetic code

A

Triplet code

23
Q

Genetic code is universal

A

All organisms use this same code

24
Q

Degenerate code

A

64 different codons possible (444) but only 20 amino acids
An amino acid can be coded for by more than one codon

25
Q

Non-overlapping

A

DNA base sequence is read from base 1 not base 2 or 3

26
Q

Nature of genetic code

A

Triplet code
Non-overlapping
Degenerate
Universal

27
Q

Synthesis of polypeptide

A

Transcription

Translation

28
Q

Transcription

A

Conversion of the genetic code to a sequence of nucleotides in mRNA
Reading the code and producing a messenger molecule to carry the code out to the cytoplasm

29
Q

Translation

A

Converting the code in mRNA to a sequence of amino acids

30
Q

Gene

A

A length of DNA that codes for one polypeptide

31
Q

Start codon

A

Signals the start of a sequence that codes for a protein

32
Q

Stop codons

A

There are 3 codons that do not code for any amino acids and signal the end of a sequence

33
Q

Process of transcription

A

DNA strands separate (same process as replication)
Sense strand contains code for protein (5’ to 3’)
Free RNA nucleotides base pair to complementary bases exposed on antisense/ template strand (3’ to 5’) - used to build copy of coding strand
RNA polymerase joins bases to form single-strand RNA (phosphodiester bonds)
mRNA detaches from DNA template and strands reform helix. mRNA leaves through nuclear pores and enters cytoplasm

34
Q

Process of translation

A

mRNA enters ribosomal groove and binds to small subunit in ribosomes
tRNA molecule carrying amino acid binds to mRNA start codon and another binds to next mRNA codon with complementary anti codons (max. 2) - these form H bonds
Peptidyl transferase causes a peptide bond to form between amino acids
Ribosome moves along mRNA, releasing first tRNA
Process stops when ribosome reaches end of mRNA with stop codon and detaches

35
Q

Conservative model

A

Proposed that that the original DNA served as a complete template so that the resulting DNA was completely new

36
Q

Dispersive model

A

Proposed that the two new DNA molecules had part new and part old DNA interspersed throughout them

37
Q

Transcription unit

A

Comprises of at least one gene but often more

38
Q

mRNA vs complementary DNA sequence

A

They’re the same but T is replaced by U

39
Q

How many base pairs are there in one full turn of the DNA double helix

A

10

40
Q

Why is the double helix structure of DNA important

A

Keep DNA stable
Enables it to fit much info in a small space
Protects bases in the middle

41
Q

Role of DNA ligase

A

Joins sugar-phosphate backbone of DNA
Catalyses formation of phosphodiester bonds
Joins promoter to gene and promoter and gene to plasmids

42
Q

How is the replication fork formed

A

When the helicase starts to break H bonds between the bases on the two antiparallel strands

43
Q

Okazaki fragments

A

Short single stranded DNA molecule complementary to DNA on lagging strand

44
Q

Do start codons code for an amino acid

A

Yes only stop codons do not

45
Q

DNA polymerase

A

Reads in the 3’ to 5’ direction and builds in the 5’ to 3’ direction

46
Q

DNA extraction procedure

A

Grind sample in pestle and mortar - break cell wall
Add detergent - breaks down csm
Add salt - breaks H bonds between DNA and water
Add protease - breaks down histones
Add ethanol - causes DNA to ppt out of sol to be collected using a glass rod

47
Q

What types of activity does the cell require energy for

A

Synthesis e.g protein
Transport
Movement - sliding filament model

48
Q

What makes ATP a good immediate energy store

A

The interconversion of ATP and ADP is constantly happening so not much ATP is required

49
Q

Properties of ATP

A

Small - moves easily in and out of cells
Water-soluble - energy requiring processes happen in aq
Easily regenerated
Releases energy is small quantities - energy not wasted as heat
Contains bonds between phosphates w/ intermediate energy - large enough to meet needs of cellular reactions

OCR A level Biology (25 decks)

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