Topic 2 - Nucleic acids Flashcards
Function of DNA and RNA
- DNA holds genetic information
- RNA transfers genetic information from DNA to ribosomes. Ribosomes are formed from RNA and proteins
Structure of DNA nucleotide
- Contains pentose sugar, nitrogenous base and a phosphate group
- deoxyribose
- adenine, thymine, guanine or cytosine
Structure of RNA nucleotide
- Contains pentose sugar, nitrogenous base and a phosphate group
- ribose
- adenine, uracil, guanine or cytosine
Structure of DNA molecule
- 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
Structure of RNA molecule
- Polynucleotide chain
- RNA molecules joined together by condensation reactions forming phosphodiester bonds
- Single RNA polynucleotide strand
Difference between DNA and RNA molecules
- 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
Structure of DNA related to it’s functions:
- 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
Process of DNA replication
- DNA helicase breaks hydrogen bonds between bases, unwinded double helix
- = two strands which both act as templates
- free floating DNA nucleotides attracted to exposed bases via specific complementary base pairing, hydrogen bonds form (a-t, g-c)
- DNA polymerase joins adjacent nucleotides on new strand by condensation, forming phosphodiester bonds (= sugar phosphate backbone)
- Replication is semi-conservative - each new strand forms contains one original/template strand and one new strand
- Ensure genetic continuity between generations of cells
DNA polymerase moves in opposite directions along DNA strands
- 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)
Evidence of semi conservative replication (Meselson and Stahl)
- 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.
The structure of ATP (adenosine triphosphate)
- Ribose
- Molecule of adenine
- 3 phosphate groups
- Nucleotide derivative
ATP hydrolysis
- 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)
ATP condensation
- ADP + Pi –> ATP
- Catalysed by the enzyme ATP synthase
- Happens during respiration or photosynthesis
- Also called phosphorylation of ADP
The properties of ATP that make it a suitable immediate source of energy
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)
How hydrogen bonding occurs between water molecules
- 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
Properties of water that make it important
- High specific heat capacity
- High latent heat of evaporation
- Cohesive
- Solvent
- Metabolite
High specific heat capacity explanation and importance
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
High latent heat of evaporation explanation and importance
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
Cohesive explanation and importance
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
Solvent explanation and importance
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
Metabolite explanation and importance
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
Inorganic ions
- 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
Phosphate: chemical symbol and role
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
Hydrogen: chemical symbol and role
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
Iron chemical symbol and role
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+
Sodium chemical symbol and role
Chemical symbol:
Na+
Role:
- Co transport of glucose and amino acids across cell membranes
- Involved in generating nerve impulses and muscle contraction
