Necleotides And Nucleic Acids Flashcards
purines
Two carbon ringed bases
Adenine
Guanine
Pyrimidines
Single carbon ring bases
Thymine
Cytosine
Uracil (in RNA)
Describe formation of DNA (6)
Nucleotides linked together by condensation
Double helix; antiparallel strands
Complementary base Pairs held by weak hydrogen bonds
Phosphodiester bonds between phosphate and pentose
5’ at one end, 3’ at the other
5’ to 3’ leading
3’ to 5 lagging
How is DNA structure suites for its role (3)
Polymer; a lot of information stored
Bass sequence; allows coding for information
Double stranded; accurate replication and makes the molecule stable
State the three theorised methods of DNA replication
Conservative
Semi-conservative
Dispersive
Semi-conservative replication, explain why it is the most efficient form of replication?
Original stand serves as template for a new complementary strand
50% old strand, 50% new
- Allows few errors to be made as original DNA acts as a template.
- Errors can be more easily corrected as original strand is still present
- New strand would see errors more likely to be ignored.
Name the enzymes involved in replication
DNA Helicase
DNA polymerase
DNA ligase
DNA Primase
DNA Helicase
Separates DNA strands by cutting through HBonda
Uses energy from ATP hydrolysis
DNA Polymerase
Catalyses the formation of phosphodiester bonds between nucleotides
Therefore causing deoxyribonucleotides to form DNA strands
Can only move from 5’ to 3’
DNA ligase
Links two DNA strands with double strand break
Structure of nucleotide
Phosphate links at 5th C on sugar forms- also links with OH group at 3rd C
Pentose sugar( ribose or deoxyribose )
Base; purine or pyrimidines
Okazaki fragments
Short piece of DNA created on lagging strand
Difference between continuous and discontinuous replication
Continuous;
Moves from 5’ to 3’
DNA polymerase binds to the end
Free nucleotides are added with no breaks
Discontinuous;
3’ to 5’ so DNA cannot bind to end
Free DNA added in sections
Forms Okazaki fragments which are sealed by DNA ligase
Why does DNA not catalyse the joining of Okazaki fragments
Enzymes are substrate specific
Nucleotides have a different shape on Okazako fragments compared to normal nucleotides
How many different types of codons are possible
64
What is the start codon
AUG
What are the 3 termination codons
UAA
UAG
UGA
Triplet(codon)
Three consecutive nucleotides
Gene
Chain of codons with a start and stop.
Transcription unit
Genes collectively coding for an end product
Briefly describe DNA replication
- DNA unzips via DNA Helicase
New DNA strands formed by free nucleotides forming complementary bonds
DNA polymerase adds nucleotides from 5’ to 3’ on leading strand
3’ to 5’ on lagging strand via Okazaki fragments
Stands rewinds together
Antisense
3’ to 5’ strand during transcription
Codes for mRNA therefore complementary to
mRNA and Sense strand
Contains anti-codons which code for the same as antisense
Sense strand
5’ to 3’ strand during transcription
Codons code for same amino acids as mRNA
Complementary to antisense
Codes for protein but not used in proteins synthesis
Anticodon
Attaches to tRNA
Complementary to mRNA codons
Ribosome in Translation
Large and small subunits
Almost same amount of protein
Forms rRNA
Small subunits bind to mRNA during translation
rRNA
Maintains structural stability of protein synthesis sequence
tRNA
Folded to allow attachment of anti codon
Carries amino acid according to anticodon
What structure does the sequence of amino acids form
Primary
Describe transcription (6)
- ) DNA unwinds and unzips using DNA helicase to break hydrogen bonds between base pairs.
- ) Strands separate into sense (5’ to 3’) and antisense (3’ to 5’) strands.
- ) Antisense strand acts as a template for the free complementary RNA nucleotides to bind to.
- ) RNA Polymerase form phosphodiester bonds between RNA nucleotides until the gene ends to form mRNA
- ) mRNA detaches from DNA. DNA rewinds into helical structure.
- ) mRNA leaves the nucleus via nuclear pore, into the cytoplasm.
Describe translation
- ) mRNA binds to the smaller subunit in the ribosome at start codon (AUG)
- ) Complementary tRNAs bring amino acids according to the anticodons
- ) Maximum of 2 tRNAs can be bound at the same time
- ) Chain of amino acids form a polypeptide which is primary structure of protein
- ) Polypeptide chain stops at ‘STOP’ codons; UGA, UAA, UAG.
- ) Polypeptide chain folds to form secondary and tertiary structures.
How is the structure of DNA suited for replication (5) and
- Double stranded with each strand acting as a template
- Complementary base pairs
- H bonds between base pairs can break easily
- purine only bond to pyrimidines
- different hydrogen bonds between AT and GC
