Nucleotides and Nucleic Acids Flashcards
Module 1
Who determined the structure of DNA and how?
Rosalind Franklin, James Watson and Francis Crick. Using X-Ray crystallography to find the structure
What are the monomers of DNA and RNA
DNA - deoxyribose sugar, phosphate and a base
RNA - ribose sugar, phosphate and a base
How are polynucleotides/nucleic acids formed
Condensation reaction forming a phosphodiester bond between the phosphate group of one nucleotide and C3 of another nucleotide
What are the two types of nitrogenous bases and what bases do they include
Purine - Adenine, Guanine
Pyrimidine - Thymine, Cytosine, Uracil
How are two strands held together in DNA
Hydrogen bonding between a pyrimidine and a purine in DNA
What is the Complementary base pair rule
A purine always bods with a pyrimidine
A-T - two H bonds
G-C - three H bonds
What does anti-parallel mean
The two DNA strands run in opposite directions
What is DNA structure like
Chain twisted every 10 nucleotides to form a double helix structure
Anti-parallel
What are the three models of DNA replication
Semi-conservative
Conservative
Dispersive
Describe Semi-Conservative replication
Takes place in the nucleus
Double Helix is untwisted by gyrase
H bonds broken by helicase
Each strand acts as a template
Free DNA nucleotides in nucleus align with exposed nucleotides
Complimentary base pairing occurs
H bonds form
Phosphodiester bonds form between free nucleotides using polymerase
Where does Semi conservative replication take place in Bacteria, Chloroplasts and mitochondria
Bacteria - nucleoid + plasmid
Chloroplasts and mitochondria - plasmid
What is the Meselson-Stahl experiment
Proved semi-conservative replication
Grew E.coli in N15
- when put through centrifuge, all E.coli moved down in Gen 0
Then placed in N14
- Hybrid strand formed in Gen 1
Gen 2 - 50% hybrid, 50% N14
What is a gene
A sequence of DNA that codes for a protein
What is transcription
transcribing a gene into a strand of mRNA
What is translation
Translating a mRNA strand into a polypeptide chain on a ribosome
What are the differences between RNA and DNA
RNA has ribose instead of deoxyribose
RNA has uracil instead of Thymine
RNA is a single strand polynucleotide
How many forms of RNA exist
3 - messenger RNA, ribosomal RNA, transfer RNA
What is messenger RNA
Copy of template strand, has codons
Involved in transcription and translation
Made in nucleolus and moves to ribosome as a template for protein synthesis
What is a codon
3 adjacent nucleotides that code for an amino acid
what is ribosomal RNA
complex molecule that accounts for half the mass of a ribosome
takes part in translation
What is transfer RNA
Small single strand (80 nucleotides)
Clover leaf shape
has binding site for specific amino acids
has unpaired triplet of bases called an anticodon
carries an amino acid to ribosome where they bond to form a polypeptide
What is the process of Transcription
Gene unwinds and helicase breaks H bonds
Only one DNA strand is used as a template strand
Free RNA nucleotides bind to complimentary base on template strand
RNA polymerase catalyses formation of phosphodiester bonds between RNA nucleotides
mRNA is complimentary to template strand and a copy of coding strand
mRNA released from DNA and goes through a nuclear pore to a ribosome
What is the process of Translation
mRNA binds to ribosome
tRNA attaches and its anticodon binds to the 1st codon of mRNA
tRNA is carrying a specific amino acid
2nd tRNA binds to 2nd exposed codon via its anticodon
peptide bond forms between 2 amino acid
ribosome moves along mRNA
1st tRNA leaves, and a 3rd tRNA brings another amino acids
Polypeptide chain grows until a stop codon is reached
What are some features of the DNA code
Order of bases = order of amino acids
read in triplets
each triplet codes for one amino acid
has stop codes
