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Biology Alevel > Nucleotides And DNA > Flashcards

Nucleotides And DNA Flashcards

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1
Q

What does a nucleotide consist of?

A

PENTOSE sugar
Nitrogen base
Phosphate group

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2
Q

What are the four bases?

A

Adenine
Cytosine
Guanine
Thymine

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3
Q

Components of RNA nucleotide?

A

Ribose sugar (Pentose) , with OH group (more susceptible to hydrolysis - makes a better transport molecule)
Phosphate group
1/4 bases

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4
Q

What are purines and pyrimidines?

A

PURINES : bases A and G - double ring structure
PYRIMIDINES : C and T - single ring structure

Purine can only pair with pyramidines due to size differences

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5
Q

How are nucleotides bonded together to form DNA/RNA ?

A
  • joined tgt via condensation reactions
    Condensation reaction occurs between PHOSPHATE GROUP and PENTOSE sugar
  • forms phosphodeister bond
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6
Q

What is the sugar phosphate backbone?

A

Chain of alternating phosphate groups and Pentose sugars , due to many phosphodister bonds

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7
Q

What is energy required for in living organisms ?

A

Anabolic reactions (building larger molecules from smaller molecules)
Moving substances across the cell membrane or moving substances within the cell
Muscle contraction– to coordinate movement at the whole-organism level
The conduction of nerve impulses

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8
Q

What is ATP?

A

energy-carrying molecule that provides the energy to drive many processes inside living cells
- type of nucleic acid

Ribose sugar , phosphate and base (adenine)

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9
Q

Adenosine nucleotide made when combined with 1, 2 and 3 phosphate groups?

A

1: AMP - adenosine monophosphate
2: ADP - adenosine diphosphate
3: ATP - adenosine triphosphate

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10
Q

Structure of DNA?

A

Made of 2 polynucleotide strands , running in opposite directions - ANTIPARALLEL (phosphodiester bonds link 5- carbon on sugar molecule to phosphate group on same molecule, which is also bonded to 3- carbon of sugar on next nucleotide)

THE POLYNUCLEOTIDE STRANDS made from deoxyribose sugars and phosphate groups bonded together (phosphodiester bond) to form the sugar - phosphate backbone

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11
Q

How are the bases held together in DNA?

A

A and T - 2 hydrogen bonds
G and C - 3 hydrogen bonds

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12
Q

What is semi conservative replication?

A
  • occurs in preparation for mitosis as DNA molecules must be doubled before mitosis

1) enzyme helicase unwinds helix - breaks Hydrogen bonds between bases , so 2 single polynucleotide DNA stands made
2) these single strands act as a TEMPLATE for formation of new strand made from free nucleotides (attracted to exposed DNA bases)
3) new nucleotides are joined together by enzyme DNA POLYMERASE , catalysing condensation reaction between deoxyribose sugar and phosphate groups to form new strand - forms sugar-phosphate backbone on new DNA strand
- DNA polymerase breaks off 2 extra phosphate/use energy released to create phosphodiester bonds
4) original strand /new strand join tgt through hydrogen bonds between base pairs

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13
Q

What is a gene?

A

sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, that in turn make up a specific polypeptide (protein)

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14
Q

What does each sequence of 3 bases code for?

A

Sequence of Amino acids

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15
Q

What’s meant by a non overlapping genetic code?

A

Every base is only Read once

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16
Q

Why is the code degenerate?

A

64 different codons (triplets) but only 20 different amino acids - multiple codons can code for same amino acids

17
Q

How is the genetic code universal?

A

Same triplet code codes for same amino acids in all living things

18
Q

What is transcription ?

A
  • hydrogen bonds between bases break and part of DNA unwinds - 2 separate strands
  • One of the DNA strands is used as a template by RNA polymerase to make the mRNA molecule
  • Free nucleotides line up by complementary base pairing
  • adjacent nucleotides are joined by phosphodiester bonds made by RNA polymerase which moves along DNA - forms single stranded molecule of mRNA
  • as RNA polymerase passes, the DNA strands reform their double helix structure
  • mRNA then detaches from DNA TEMPLATE once stop codon is reached and moves out of the nucleus through a pore and attaches to a ribosome in the cytoplasm
19
Q

What is translation?

A
  • mRNA attaches to a ribosome and transfer RNA collects amino acids from the cytoplasm and carries them to the ribosome
  • tRNA attaches itself to mRNA by complementary base pairing - 2 tRNA molecules attach to mRNA at once
  • The amino acids attached to two tRNA molecules join by a peptide bond - formation is catalysed by rRNA and then tRNA molecules detach themselve, leaving them behind
    • process repeated as ribosome moves along mRNA strand until stop codon reached leading to the formation of a polypeptide chain
20
Q

Differences between dna replication and transcription

A
  • in transcription, only small section of DNA unzips (where gene is located)
  • from 2 daughter strands of DNA vs one strand of mRNA
  • RNA /DNA free nucleotides
  • DNA vs RNA polymerase
  • different helicase enzymes
21
Q

PRACTICAL: DNA purification

A
  1. Place the ethanol in a freezer 24 hours before starting the investigation
  2. Cut up the onion into small pieces (5 mm × 5 mm) - break down cell walls
  3. Add the washing-up liquid to 90 cm³ of tap water in a beaker
    Add some of the onion pieces to the beaker
  4. Place the beaker in a water bath at 60 °C for 15 minutes - detergent/high temp damages phospholipid bilayer releasing DNA
  5. Cool the mixture in an ice-water bath for 5 minutes, stirring it continually- lower temperature prevent breaking down if DNA
  6. Pour the mixture into a blender and blend for 5 seconds - breaks cell walls/membranes releasing more DNA
  7. Using the filter paper, filter the mixture into another beaker
  8. Pour 10 cm³ of the filtrate into a test tube and add 2-3 drops of protease enzyme, mixing well - removes proteins - leaves DNA
  9. Carefully add the ice-cold ethanol to the test tube and wait 2-3 minutes
    Nucleic acids are insoluble in ice-cold ethanol and so the DNA forms a precipitate white layer) at the top of the test tube mixture
22
Q

How is DNA and RNA different?

A

→ RNA contains ribose sugar
→ nucleotides in RNA form single polynucleotide strand
→ RNA contains uracil instead of thymine

23
Q

What are histones and their function

A
  • Histones are DNA-binding proteins.
    DNA wraps around histones

Function : package DNA

24
Q

Components of DNA nucleotides?

A

A deoxyribose sugar with hydrogen at the 2’ position
A phosphate group
One of four nitrogenous bases

25
Q

Semi conservative ?

A

One strand is new,one strand is original
Each DNA strand acts a template

Biology Alevel (24 decks)

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