Topic 1B: More Biological Molecules Flashcards
What is the structure of a nucleotide?
- Pentose sugar
- Nitrogenous base
- Phosphate group
What is the structure of a DNA nucleotide?
- Deoxyribose
- Nitrogenous base –> Adenine, Thymine, Cytosine, Guanine
- Phosphate group
What is the structure of a RNA nucleotide?
- Ribose
- Nitrogenous base –> Adenine, Uracil, Cytosine, Guanine
- Phosphate group
How do polynucleotides form?
- Condensation reaction between the phosphate group of one nucleotide and the sugar of the next
- Forms phosphodiester bonds to form the sugar-phosphate backbone
Which bases are pyrimidines and and how many rings do they have?
- Cytosine, Thymine
- 1 ring
Which bases are purines and how many rings do they have?
- Adenine, Guanine
- 2 rings
Which bases bond to which and with how many bonds?
- A - T –> 2 bonds
- C - G –> 3 bonds
- All bonds = hydrogen bonds
How is DNA structured?
- Complimentary base pairing between strands
- Strands are antiparallel so the structure twists to a double helix shape
How is RNA different to DNA?
- U not T
- Single stranded
- Much shorter
What is the model for DNA replication called and how does it work?
- Semi-conservative model
- Each daughter DNA has one parent strand and one new strand
How does DNA replication occur?
- DNA helicase breaks H bonds between base pairs to separate the strands
- Each strand acts as a template as free nucleotides move in to bond to a complimentary base
- DNA polymerase forms phosphodiester bonds between the free nucleotides to make the sugar-phosphate backbone of the new complimentary strand
How does DNA polymerase work on each strand differently?
- The active site of DNA polymerase is only complimentary to the 3’ end
- As the strands are antiparallel the enzyme works in different directions on each
- This makes a leading strand and a lagging strand
Which scientists did the investigation to give evidence for DNA replication as the semi-conservative model?
Meselson and Stahl
Which isotopes of nitrogen are used to give evidence in DNA replication?
14N and 15N
How does the experiment work to give evidence of DNA replication?
- Bases = nitrogenous so takes in N in DNA replication
- As different isotopes are used the DNA has differing masses
- This can be found using a centrifuge to separate the strands by density
- This provides evidence of semi-conservative DNA replication
Describe the generations of DNA replication in nitrogen isotopes
- G0 = 100% 15N 15N –> all heavy –> all settle to the bottom
- G1 = each strand is half new with lighter N and half is old with heavier N –> 100% 15N 14N –> all settles slightly further up
- G2 = now 2 are fully lighter N and 2 are split –> 50% 15N 14N, 50% 14N 14N –> half settles further up than the other half
- G3 = only 2 in 8 have half heavy –> 75% 14N 14N, 25% 15N 14N –> bigger settlement further up than a smaller one
What about the structure of water makes it special?
- It is a polar molecule
- O side = slightly -ve
- H side = slightly +ve
What is hydrogen bonding?
- The slightly -ve O attract the slightly +ve H of other water molecules
How is water a metabolite?
- Metabolic reactions usually involve condensation or hydrolysis –> water is an essential part of this
How does high latent heat of vaporisation help water?
- Takes lots of energy to break all the hydrogen bonds in water for it to evaporate
- Useful for living organisms –> use water evaporation in sweat to cool down –> takes lots of energy with it with as minimal water loss as possible
How does high specific heat capacity help water?
- Hydrogen bonds between water molecules can absorb lots of energy
- Water doesn’t have rapid temp changes –> stable living environment
- Also water in an organism has a fairly constant temperature
How is water a good solvent?
- Many substances are ionic so have charged particles –> these are attracted to the polar ends of water so that they are totally surrounded by water molecules
What is cohesion and how does this relate to water?
- Cohesion = attraction between molecules of the same type
- Water molecules are very cohesive because they are polar
- Helps water to flow to transport substances
- Has high surface tension –> sweat forms droplets + animals like pond skaters can ‘walk’ on water
What is the structure of ATP?
- Adenine base
- Ribose sugar
- 3 phosphate groups
- Called a nucleotide derivative as it is a modified version of a nucleotide
How is ATP produced?
- When energy is released from glucose it is used to make ATP
How is ATP used?
- When energy is needed ATP is hydrolysed to ADP and Pi
- The phosphate bond is broken releasing energy
- Catalysed by ATP hydrolase
- Can be coupled to an energy requiring reaction to be directly put to use
- ATP can be resynthesised by ATP synthase
What is the inorganic phosphate used for?
- Can be added to another compound to make it more reactive –> phosphorylation
What are inorganic ions and where are they usually found?
- Charged atoms
- Don’t usually contain carbon
- Found in solution in cytoplasm and bodily fluids
What are iron ions used for?
- Fe 2+
- Haemoglobin = 4 different polypeptides each with an iron ion in the centre
- Fe 2+ binds to oxygen –> temporarily becomes Fe 3+ until the oxygen is released
What do hydrogen ions do?
- H +
- pH is based on concentration of H+ ions and enzyme controlled reactions are affected by pH
What do Sodium ions do?
- Na +
- Help glucose or amino acids to be transported into a cell by co transport
What do phosphate ions do?
- Po4 3-
- When attached to another molecule they are a phosphate group
- Phosphate groups are in DNA, RNA, ATP
- In DNA + RNA they allow nucleotides to join to polynucleotides
