Lecture 1 - DNA
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what are the components of DNA
• its a nucleic acid -a macromolecule made up of 2 polynucleotide chains • nucleotides consist of deoxyribose, a nitrogen containing base (adenine, thymine, guanine or cytosine), a phosphate group • the base is connected to carbon 1 -the 3’ carbons hydroxyl group will join to the adjacent nucleotide
what makes up a nucleoside?
sugar and base
whats the bond that connects the sugar and base
N-glycosidic bond
what do phosphodiester bonds do
connect adjacent nucleotides, to create the sugar phosphate backbone
what bond connects the bases of opposite strands and how many of these bonds
-hydrogen bonds -A and T have 2 -C and G have 3
what bases connect with which?
adenine and thymine cytosine and guanine
which bases are pyrimidines and which are purines?
-adenine and guanine are purines -thymine and cytosine are pyrimidines
is DNA a right or left handed helix?
right
what is important about the grooves in DNA?
-some proteins need to interact with the DNA and the bases and some cases need to pull apart bases and these grooved provide access to the DNA and bases
How do nucleotides join together?
• a condensation reaction, which eliminates water -this creates a 3’,5’ phosphodiester bond
why is DNA replication important in cell division?
when a cell divides, both daughter cells must receive a complete set of genes, so the DNA molecules (chromosomes) must replicate accurately before division
what happens in asexual reproduction?
1- the entire genome is on one circular chromosome = DNA molecule 2-the chromosome replicates once to produce two chromosomes that are identical (except for rare chromosomes) 3-the two identical daughter chromosomes move toward opposite end of the cell 4-when the cell divides the daughter chromosomes are partitioned one to each daughter cell
why does replication need to be accurate?
so the daughter cell ends up with two copies of the genome, identical or near identical to the parent
what happens in M phase in the cell cycle?
mitosis and cytokinesis
what happens in G1 and G2?
transcription of genes
what happens in S phase?
it depends where the genes are in the genome and how the replication process is going as to whether transcription can occur in those genes or not
is DNA replication semi-conservative?
yes
where do each strand come from in DNA replication
one from the parent and one is a new strand
what strand determines the sequence of the newly synthesised strand
the template strand
which end of the molecule do the nucleotides add onto
3’ end
is DNA parallel or anti-parallel?
anti-parallel
what happens in DNA replication?
1-the strands separate 2-a new strand is made using each old strand as a template according to the rules of base pairing
what direction does DNA synthesis occur in?
5’ to 3’ direction
what does helicase do in replication?
unwinds double helical DNA, giving all other proteins required access to the template