nucleic Acids dna Flashcards
Describe the role of DNA polymerase in DNA replication
Joins nucleotides (to form new strand)
Name two scientists who proposed models of the chemical structure of DNA and DNA replication
Watson and Crick
Role of single stranded DNA fragments and DNA nucleotides in semi-conservative replication
Template
Determines order of nucleotides
Forms complementary pairs A-T/C-G
Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA.
Prokaryotic DNA is circular, SMALLER/SHORTER , not associated with histones and has no introns
Deacribe the main role of DNA (2)
• Carries the genetic code
• instructions for making proteins/codes for primary structure of proteins
Controls cells activities
The nucleic acid which never leaves the nucleus in a eukaryotic cell is…
DNA
Grasshoppers and humans have very similar percentages of each base in their DNA but are not the same class of organism. Use your knowledge of Dna structure and function to explain this
•Grasshoppers and humans have a different sequence of bases which therefore produce different proteins
Describe the term frame-shift mutation and evaluate impact of this mutation on phenotype of the organism
A frame shift mutation is
• A deletion or addition of a base
• That occurs during DNA replication
• Causes all downstream triplets to shift by one base
EFFECTS
• It results in a different protein being synthesised
• Likely loss of function for that gene or possible new function arising from the new protein
• If mutation occurs in an intron, it is possible that there is no effect
Suggest why most mutations in eukaryotic cells are regarded as neutral
• The mutation has no effect on the phenotype of the organism
• They occur in the genes are not expressed in that cell
• They occur in introns
• They are silent mutations
Identify 2 environmental factors that increase rate of mutation and describe their interaction with DNA
DNA reactive chemicals such as some bacteria viruses
• High energy ionising radiation E.g- X-rays and gamma rays
• Toxic chemicals such as benzene bromine
• They interfere with base pairing
The 2 strands of DNA are described as antiparallel. Explain meaning of antiparallel
Two strands run alongside each other, but in opposite directions
Why can nucleotides only be added in a 5’ to 3’ direction
• DNA polymerase has a specific active site that only binds to the 5’ , 5’ and 3’ are different shapes
Suggest a structural feature of DNA that boosts its protection from chemical attack
• Dna has a double helix
• so compact
Compare the structures and functions of DNA and RNA
FUNCTIONS
• Dna carries genetic information WHEREAS Rna transfers the genetic information to the ribosomes
SIMILARITIES
• Both are polymers of nucleotides
• Both have phosphodiester bonds/sugar phosphate backbone
• Both have 4 bases
DIFFERENCES
• DNA contains deoxyribose sugar whereas Rna contains ribose sugar
• Rna molecules are smaller than DNA
• DNA contains thymine bases, RNA contains uracil bases
Other than use for replication, give one advantage of DNA molecules having 2 strands
• Provides stability
• protects bases (from mutations)
Describe and explain the structure of DNA
-sugar phosphate backbone/double stranded so provides strength/stability/protects bases
• large molecule so can store lots of information
• helical- so compact
• base sequence allows information to be stored
• Double stranded so replication can occur semi-conservatively
• Complementary base pairing (A-T and C-G) so accurate replication
• many hydrogen bonds so stable
Why does DNA replicate semi-conservatively
• This ensures genetic continuity
Mesellson and Stahl experiment steps
•Bacteria were cultured on a heavy nitrogen (15N) medium
•Bacteria took up this nitrogen and used it to synthesise DNA bases
•After the Dna is extracted and spun in a centrifuge it settled near the bottom of the tube
• The bacteria is then transferred to light nitrogen medium
• After period of time DNA extracted and centrifuged, it settled in an intermediate position
Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein
• Change in primary structure changes sequence of amino acids
• So hydrogen,disulphide and ionic bonds form in different positions
• This alters the tertiary structure of the enzyme
Active site no longer complementary to substrate
• So no E-Z complexes can be formed
Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA.
- Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip;
- Two strands, so both can act as templates;
- Complementary base pairing allows accurate replication
Differences between DNA and RNA
DNA has deoxyribose, thymine, and is double-stranded. RNA has ribose, uracil, and is single-stranded
State and explain the property of water that can help to buffer changes in temperature
Water has high specific heat capacity.
So it takes a lot of energy to change temperature.
Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)
•ATP is an immediate source of energy
•ATP only releases a small amount of energy at a time
Explain 5 properties of water
Metabolite in condensation reactions
A solvent so metabolic reactions can occur
High specific heat capacity so buffers changes in temperature
Latent heat of vaporisation so provides a cooling effect
Cohesion so supports columns of water
Cohesion so produces surfaces tension for small organisms
