2.1.3 Nucleotides And Nucleic Acids Flashcards
Structure of a nucleotide
Pentose monosaccharide
Phosphate group
Nitrogenous base
Structure of nucleic acids
Large polymers formed from nucleotides
How are nucleotides joined
Condensation reactions
Phosphate group on carbon 5 forms a covalent bond with hydroxyl group on carbon 3
Phosphodiester bond
Forms long, strong sugar-phosphate backbone
Difference in structure between ribose and deoxyribose
Deoxyribose has one less oxygen, on carbon 2 it has 2 H atoms attached
Ribose has one H atom and a hydroxyl group attached to carbon 2
What are pyrimidines
Smaller bases, contain single carbon ring structures
T and C
What are purines
Larger bases, contain double carbon ring structures
A and G
What are ADP and ATP
Phosphorylated nucleotides
Structure of ADP
Adenine, ribose, two phosphate groups
Structure of ATP
Adenine, ribose, 3 phosphate groups
Structure of DNA
Made of 2 strands of polynucleotides coiled into double helix
Two strands held together by hydrogen bonds
Each strand phosphate group (5’) at one end at a hydroxyl group (3’) at the other end
2 parallel strands arranged antiparallel
What is complementary base pairing
Adenine and thymine form 2 H bonds
Cytosine and Guanine form 3 H bonds
How do DNA and RNA nucleotides differ
Pentose sugar in DNA is deoxyribose
Pentose sugar in RNA is ribose
Thymine base is uracil in RNA
How to carry out DNA extraction
Grind sample in pestle and mortar (breaks down cell walls)
Mix sample with detergent (breaks down cell membrane and releases cell content into solution)
Add salt (breaks H bonds between DNA and water)
Add protease (break down proteins associated with DNA in nuclei)
Add layer of ethanol (precipitates DNA out of solution)
DNA is seen as white strands, can be picked up on a glass rod
What is semi-conservative replication
In replication, the double helix must unwind and H bonds must be broken to separate strands
Free nucleotides pair with complementary bases and H bonds form
New nucleotides join with phosphodiester bonds
Each new strand is half old and half new (semi-conservative)
Role of DNA helicase in replication
Unzips
Unwinds the double helix and separates the 2 strands
Travels along backbone, catalysing reactions that break H bonds between complementary base pairs
Role of DNA polymerase in replication
Catalyses formation of phosphodiester bonds between free nucleotides
Always acts from the 5’ end to the 3’ end (phosphate to OH ) as it can only bind to 5’ end
What’s the triplet code
3 bases form a codon, each codon codes for an amino acid
What is a gene
Section of DNA that contains the complete sequence of codons to code for an entire protein
What does the genetic code being universal mean
All organisms use the same code
What does DNA being degenerate mean
Amino acids can be coded for by more than one codon
How is DNA non-overlapping
Start codons placed at the start of a gene signal start of sequence that codes for protein, stop codons signal end of sequence
This means its always read in order, non-overlapping
Why does transcription occur
DNA is contained within nuclear envelope but protein synthesis occurs at ribosomes in cytoplasm
Chromosomal DNA molecule is too large to leave nucleus
Describe the process of transcription
Section of DNA that contains the gene needed unwinds and unzips due to DNA helicase
The sense strand which runs 5’ to 3’ contains the code for the protein to be synthesised
The other is the antisense strand as acts as a template strand during transcription
Free RNA nucleotides base pair with complementary bases exposed on antisense strand
Phosphodiester bonds formed by RNA polymerase
mRNA formed
Detaches from DNA template and leaves nucleus through nuclear pore, travels to ribosome
Double helix reforms
Describe the process of translation
mRNA binds to specific site on small subunit of a ribosome, holds it in position whilst its translated to sequence of amino acids
tRNA’s anticodon binds to complementary codon on mRNA and tRNA molecules carry an amino acid corresponding to the codon
As tRNA anticodons bind to complementary codons along mRNA, amino acids are brought together one at a time in correct sequence to form primary structure
Ribosomes are the binding site for mRNA and tRNA and catalyse assembly of protein
Ribosome moves along the mRNA strand until it reaches the stop codon and the polypeptide is released
As the AA are joined, they fold into secondary and tertiary structures
Structure of tRNA
Strand of RNA folded so that 3 bases (anticodon) are at one end of the molecule
