Section 1- Nucleic acids Flashcards
What is the semi-conservative model in DNA replication?
Original DNA molecule splits into 2 separate stands
Strands acted as templates
1 old strand, 1 new strand
Who proposed the evidence for the semi-conservative model?
Watson and Crick
What was the Meselson and Stahl experiment into semi-conservative replication?
Used 2x Nitrogen isotopes
- Grew E.Coli for several generations in each isotope
- DNA isolated and centrifuged
DNA formed separate bands according to densities - E.Coli from 15N moved with 14N
After 1 generation band in between space formed
What are individual nucleotides made up of?
Pentose sugar
Phosphate group
Nitrogen-containing organic base
What reaction occurs to produce a nucleotide?
Condensation reaction
What bond is formed between nucloetides?
Phosphodiester bond
What is the sugar in RNA?
Ribose sugar
What bond joins 2 DNA strands?
Hydrogen bond
In 1953, what did Watson and Crick discover?
Structure of DNA
Why is DNA a stable molecule?
Phosphodiester backbone protects more chemically reactive organic bases inside double helix.
3 Hydrogen bonds between C-G, the higher proportion of G-C pairings, the more stable the DNA molecule.
How is a DNA molecule adapted to carry out its functions?
Very stable structure which passes from generation to generation without significant change
Hydrogen bonds allow separation during DNA replication
Extremely large so carries large amount of genetic material
Why can nucleic acids only be synthesised in the 5’-to-3’ direction?
DNA polymerase can only attach nucleotides to the hydroxyl group on the 3’ carbon molecule.
What is the pentose sugars in DNA & RNA?
DNA: deoxyribose
RNA: ribose
What is the role of DNA in living cells?
Base sequence of genes codes for functional RNA & amino acid sequence of polypeptides.
Genetic information determines inherited characteristics
Which bases are purine and which are pyrimidine?
A & G = 2-ring purine
T & C & U = 1-ring pyrimidine
What is the process of semi-conservative DNA replication?
- DNA helicase breaks H-bonds between base pairs.
- Each strand acts as a template.
- Free nucleotides attach to exposed bases by complementary base pairing.
- DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand.
- Hydrogen bonds form.
Why is the process of DNA replication described as semi-conservative?
Half the original DNA is built into the new DNA strand
If an inhibitor of DNA polymerase were introduced into a cell, what would the effect on DNA replication be?
Linking together of new nucleotides could not take place.
What is the structure of ATP?
Adenine
Ribose
3 phosphates
What is the role of ATP in cells?
ATP hydrolase catalyses ATP into ADP + Pi
Energy released is coupled to metabolic reactions
Phosphate group phosphorylates compounds to make them more reactive.
How is ATP resynthesised in cells?
ATP synthase catalyses condensation reaction between ADP + Pi
During photosynthesis and respiration.
Why is ATP suitable as the ‘energy currency’ of cells?
High energy bonds between phosphate groups
Small amounts of energy released at a time = less waste
Single-step hydrolysis = energy available quickly
Readily resynthesised
What are the 3 ways a phosphate molecule is added to ADP to make ATP?
In chlorophyll containing plant cells during photosynthesis (photophosphorylation)
In plant and animal cells during respiration (oxidative phosphorylation)
In plant and animal cells when phosphate groups are transferred from donor molecules to ADP
Why is ATP a better immediate energy source than glucose?
Each ATP molecule releases more energy than each glucose molecule
The hydrolysis of ATP to ADP is a single reaction that releases immediate energy.
Breakdown of glucose is long series of reactions.
What processes is ATP in cells used for?
Metabolic processes
Movement
Active transport
Secretion
Activation of molecules
Why is ATP referred to as an ‘immediate energy source’?
ATP releases its energy very rapidly.
Energy is released in a single step and is transferred directly to the reaction requiring it.
How can ATP make an enzyme-catalysed reaction take place more readily?
ATP provides a phosphate that can attach to another molecule, making it more reactive and so lowering its activation energy.
Enzymes have less ‘work’ to do and so function more readily.
What are 3 roles of ATP in plant cells?
Building up macromolecules
Active transport
Secretions
Activation of molecules
Why is water a polar molecule?
O is more electronegative that H so attracts the electron density in the covalent bond more strongly.
What are 4 biologically important properties of water?
Metabolite- used for hydrolysis reaction
Solvent for chemical reaction in the body - readily dissolves other substances
High specific heat capacity
High latent heat of vaporisation
Cohesion between molecules
Why is water significant to living organsims?
Solvent for polar molecules during metabolic reactions
Enables organisms to avoid fluctuations in core temperature
Cohesion-tension of water molecules in transpiration stream
What are inorganic ions and where are they found in the body?
Ions that do not contain carbon atoms
Found in cytoplasm
May be in high or very low concentrations
What is the role of hydrogen ions in the body?
High concentration of Hydrogen ions = low pH
Hydrogen ions interact with Hydrogen bonds & ionic bonds in tertiary structure of proteins which can cause them to denature
What is the role of iron ions in the body?
Iron ions bond to porphyrin ring to form haem group in haemoglobin
What is the role of sodium ions in the body?
Involved in co-transport of absorption of glucose and amino acids
What is the role of phosphate ions in the body?
Component of: DNA ATP NADP cAMP
Why is having a high latent heat of vaporisation important in living organisms?
Cooling effect by evaporation
What are 2 ways in which the properties of ATP make it a suitable source of energy in biological processes?
Energy released in small amounts
Soluble
Involves a single reaction
Apart from respiration, what are uses of ATP?
Active transport
To produce glycogen
Exocytosis
Cell division
DNA synthesis
What is the role of DNA polymerase in DNA replication?
Joins nucleotides
How does ice floating on the top of a pond help organisms to survive?
Ice is less dense as molecules spread out
Molecules form lattice
Causes an insulating layer
Water doesn’t freeze so organisms can still move
How does water acting as a solvent for ions such as nitrates, help organisms to survive in ponds?
Ions are polar which interact with water
Plants uptake minerals for amino acids
