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Biology > Topic 2 - Nucleic acids > Flashcards

Topic 2 - Nucleic acids Flashcards

1
Q

Function of DNA and RNA

A
  • DNA holds genetic information
  • RNA transfers genetic information from DNA to ribosomes. Ribosomes are formed from RNA and proteins
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2
Q

Structure of DNA nucleotide

A
  • Contains pentose sugar, nitrogenous base and a phosphate group
  • deoxyribose
  • adenine, thymine, guanine or cytosine
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3
Q

Structure of RNA nucleotide

A
  • Contains pentose sugar, nitrogenous base and a phosphate group
  • ribose
  • adenine, uracil, guanine or cytosine
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4
Q

Structure of DNA molecule

A
  • polynucleotide chain
  • DNA nucleotides joined together by condensation reactions forming phosphodiester bonds
  • 2 strands joined in antiparallel, held together by hydrogen bonds between specific complementary base pairs, twisting into a double helix
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5
Q

Structure of RNA molecule

A
  • Polynucleotide chain
  • RNA molecules joined together by condensation reactions forming phosphodiester bonds
  • Single RNA polynucleotide strand
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6
Q

Difference between DNA and RNA molecules

A
  • DNA molecules have the pentose sugar deoxyribose whereas RNA nucleotides have the pentose sugar ribose
  • DNA nucleotides can have the base thymine, whereas RNA nucleotides have uracil instead
  • DNA molecules are double stranded (double helix) whereas RNA molecules are single stranded
  • DNA is longer whereas RNA is shorter
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7
Q

Structure of DNA related to it’s functions:

A
  • Double stranded - both strands can act as templates for semi-conservative replication
  • Weak hydrogen bonds between bases - can be unzipped for replication
  • Complementary base pairing - accurate replication
  • Many hydrogen bonds between bases - stable/strong molecule
  • Double helix with sugar phosphate backbone - protects bases / H bonds
  • Long molecule - store lots of genetic infomation (that codes for polypeptides)
  • Double helix (coiled) - compact
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8
Q

Process of DNA replication

A
  1. DNA helicase breaks hydrogen bonds between bases, unwinded double helix
  2. = two strands which both act as templates
  3. free floating DNA nucleotides attracted to exposed bases via specific complementary base pairing, hydrogen bonds form (a-t, g-c)
  4. DNA polymerase joins adjacent nucleotides on new strand by condensation, forming phosphodiester bonds (= sugar phosphate backbone)
  5. Replication is semi-conservative - each new strand forms contains one original/template strand and one new strand
  6. Ensure genetic continuity between generations of cells
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9
Q

DNA polymerase moves in opposite directions along DNA strands

A
  • DNA has antiparallel strands
  • DNA polymerase is an enzyme with a specific shaped active site which can only bind to substrate with a complementary shape
  • Can only bind to and add nucleotides to the phosphate (3’) end of the developing trend (so works in a 5’ to 3’ direction)
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10
Q

Evidence of semi conservative replication (Meselson and Stahl)

A
  • Bacteria grown in a nutrient solution containing heavy nitrogen (15N) for several generations
  • nitrogen incorporate into bacterial DNA bases
  • Bacteria then transferred to a nutrient solution containing light nitrogen (14N) and called to grow and divide twice.
  • During this process, DNA from different samples of bacteria was extracted, suspended in a solution in separate tubes was spun in a centrifuge.

Sample 1. DNA from bacteria grown for several generations in nutrient solution containing 15N
–> DNA molecules contain 2 ‘heavy’ strands

Sample 2. DNA from bacteria grown originally in a nutrient solution containing 15N, then transferred for one division to a solution containing 14N
–> DNA molecules contain 1 original ‘heavy’ and 1 new ‘light’ strand

Sample 3. DNA from bacteria grown originally in a nutrient solution 15N, then transferred for two divisions to a solution containing 14N
–> 50% DNA molecules contain 1 ‘heavy’ strand and 1 new ‘light’ strand, 50% contain both ‘light’ strands.

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11
Q

The structure of ATP (adenosine triphosphate)

A
  • Ribose
  • Molecule of adenine
  • 3 phosphate groups
  • Nucleotide derivative
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12
Q

ATP hydrolysis

A
  • ATP –> ADP + Pi
  • Catalysed by the enzyme ATP hydrolase
  • Can be coupled to energy requiring reactions within cells, to provide energy for active transport, protein synthesis, etc.
  • The inorganic phosphate released can be used to phosphorylate other compounds e.g. glucose, often making them more reactive (i.e. lowers the activation energy)
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13
Q

ATP condensation

A
  • ADP + Pi –> ATP
  • Catalysed by the enzyme ATP synthase
  • Happens during respiration or photosynthesis
  • Also called phosphorylation of ADP
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14
Q

The properties of ATP that make it a suitable immediate source of energy

A

IMPORTANT - ATP cannot be stored
- ATP releases energy in small, manageable amounts (no energy wasted)
- Only one bond is hydrolysed (single reaction) to release energy (which is why energy release is immediate)

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15
Q

How hydrogen bonding occurs between water molecules

A
  • Water is a polar molecule (oxygen molecule has a partial negative charge; hydrogen atoms have a partial positive charge)
  • Slightly negatively charged oxygen atoms attract slightly positive charged hydrogen atoms of other water molecules
  • Hydrogen bonds form between water molecules
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16
Q

Properties of water that make it important

A
  • High specific heat capacity
  • High latent heat of evaporation
  • Cohesive
  • Solvent
  • Metabolite
17
Q

High specific heat capacity explanation and importance

A

Explanation:
- Polar so many H bonds form between water molecules
- These allow water to absorb a relatively large amount of heat energy before its temperature changes

Importance:
- Good habitat for aquatic organisms
- Organisms most made of water so helps to maintain a constant internal body temperature - important as temperature affects enzyme activity

18
Q

High latent heat of evaporation explanation and importance

A

Explanation:
- Polar so many H bonds form between water molecules
- These can absorb a lot of energy before breaking, when water evaporates

Importance:
- Evaporation of small amount of water (e.g. sweat) is an efficient cooling mechanism
- Helping organisms maintain constant body temperature

19
Q

Cohesive explanation and importance

A

Explanation:
- Polar so many H bonds form between water molecules
- So water molecules tend to stick together

Importance:
- Column of water doesn’t break when pulled up a narrow tube e.g. xylem during transpiration
- Produces surface tension at an air water surface so invertebrates can walk on water e.g. pond skaters

20
Q

Solvent explanation and importance

A

Explanation:
- Polar (has a slightly positive and negative ends)
- Can separate (dissolve) ionic compounds

Importance:
Can dissolve other substances e.g. inorganic ions, enzymes, urea, etc. so water…
- Acts as a medium for metabolic reactions (which can happen in water)
- Acts as a transport medium e.g. in xylem to transport nitrates which are needed to make amino acids

21
Q

Metabolite explanation and importance

A

Explanation:
- Water is reactive

Importance:
Condensation releases H2O and forms a chemical bond; hydrolysis requires H2O to break a bond; e.g. amino acids joined by condensation reactions for form polypeptides

22
Q

Inorganic ions

A
  • Occur is solution in the cytoplasms and body fluids of organisms
  • Some in high concentrations and others in very low concentrations
  • Each type of ion has a specific role, depending on it properties
23
Q

Phosphate: chemical symbol and role

A

Chemical symbol:
PO4-3

Role:
Attached to other molecules as a phosphate group for example:
- In DNA nucleotides, enabling nucleotides to join together forming phosphodiester bonds
- In ATP - bonds between these store / release energy

24
Q

Hydrogen: chemical symbol and role

A

Chemical symbol:
H+

Role:
Maintain pH levels in the body
- Too much H+ = acidic (low pH)
- Too little H+ = alkaline (high pH)
- Affects rate of enzyme controlled reactions as can cause enzymes to denature

25
Q

Iron chemical symbol and role

A

Chemical symbol:
Fe2+

Role:
- Component of (haem group of) haemoglobin which is contained in red blood cells
- Transports oxygen around the body - oxygen temporarily binds to it, so it becomes Fe3+

26
Q

Sodium chemical symbol and role

A

Chemical symbol:
Na+

Role:
- Co transport of glucose and amino acids across cell membranes
- Involved in generating nerve impulses and muscle contraction

Biology (16 decks)

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