DNA Flashcards
what are genes?
sections of DNA which code for particular protein and amino acid
what type of molecule is DNA?
macromolecule of chain of nucleotides
what does a nucleotide consist of?
- pentose group (ribose/deoxyribose)
- phosphate group
- nitrogenous-containing base
how do the sugar and phosphate group link?
by condensation reaction
- forms a sugar-phosphate backbone
- this enables mononucleotides to be linked together
what is a dinucleotide?
two mononucleotides linked together by sugar-phosphate backbone
what is a polynucleotide?
long chain of mononucleotides
what are the base groups?
- cytosine
- guanine
- adenine
- thymine
- uracil
what are the two complementary pairs?
- C G
- A T
how many hydrogen bonds do CG have?
three
how many hydrogen bonds do AT have?
two
what is different about the base groups in RNA?
uracil instead of thymine
which base groups are pyrimidines?
- cytosine
- uracil
- thymine
(made of one 6-sided ring and one 5-sided ring)
which base groups are purines?
- adenine
- guanine
( made of one 6-sided ring)
how does DNA form double helix?
- 2 polynucleotides held together by hydrogen bonds
- strands are anti parallel so they are synthesises in opposite directions from 5’ to 3’
when does DNA replication occur?
during interphase
how does DNA unzip initially?
- double helix unwinds
- DNA helicase unzips strand by breaking hydrogen bonds between nitrogenous bases - 3 between CG and 2 between AT
how do free nucleotides join?
- there are free nucleotides in nucleus
- DNA polymerase reads off template strand and links nucleotides by way of complementary base pairing (purines/pyrimidines) - CG/ AT1
how is new strand linked?
- new strand is linked together
- form sugar-phosphate backbone joined by covalent bonds
how does the strands being antiparallel affect the replication?
- strands are antiparallel so replication occurs backwards in one strand and forward in the other
why is it called semi-conservative replication?
two DNA molecules containing parent strand and newly synthesised strand called daughter strand so it is semi-conservative as old strand remains
what were other models for DNA replication?
- conservative model: keep old helix - form another one
- dispersive replication: replicated in fragments
what did Watson-Crick use to prove the semi-conservative replication model?
radioactive isotopes N15 and N14
