DNA 2/18 - 2/28

DNA

genetic instructions for the creation of proteins

monomer of DNA

nucleotides

nucleotide pairs

• adenine and thymine

• cytosine and guanine

purine

have a double ring structure (adenine and guanine)

pyrimidine

have a single ring structure (thymine and cytosine)

ladder model

sugar - phosphate backbone and nucleotide rungs

semi-conservative replication

parental DNA splits and each strand is used to form a new piece

messelson + stahl experiment

• determined semi-conservative replication

• grew bacteria in nitrogen 15 then switched it to nitrogen 14

• found the densities/weights and compared them

origins

location where DNA replication begins

prokaryotic origins

only have one

eukaryotic origins

have several

helicase

unwinds and opens the strands of DNA to make replication bubbles

topoisomerase

keeps the 2 strands unwound

single strand binding proteins

bind to unpaired bases, helping keep the 2 strands apart

primase

lays down an RNA primer

DNA polymerase III

binds to the primer and makes the new DNA 5’ to 3’

DNA polymerase I

removes the primers and replaces them with DNA

DNA ligase

connects the fragments together

problem: ends get shorter

solution: telomeres (composed of DNA meant to be wasted) sit at the ends of DNA strands

problem: mutations

solution: proof-reading

proof-reading

1. nuclease (cuts out the mutation)

2. polymerase (puts in the proper nucleotides)

3. ligase (connects it back together)

chromosomes in cells

• 46 in somatic

• 23 in gamete

karyotype

picture of chromosomes

nucleosomes

a strand of DNA wrapped around histones

histones

proteins that provide structure to chromosomes

chromatin

• many nucleosomes wrapped around each other

• most commonly found in the cell

chromosomes

• more tightly wound chromatin

• found during cell division

G1 (gap 1)

growth, normal functions

S (synthesis)

DNA replication occurs

G2 (gap 2)

growth, prepare for division

M (mitosis)

cell division

interphase

• G1, S, and G2

• loose chromatin

• normal cell functions

• when a cell is not dividing

prophase

• chromatin condenses to form mitotic chromosomes

• centrosomes migrate to each pole and spindle fibers form

prometaphase

• nucleus disappears

• spindle fibers attach to kineticore of chromosomes

metaphase

chromosomes line up individually at the metaphase plate (equator)

anaphase

sister chromatids move to each pole (motor proteins)

telophase/cytokinesis

• nuclei reform

• cell splits in two

• 2 genetically identical daughter cells form

cytokinesis in animal cells

cleavage furrow, a contractile ring of actin

cytokinesis in plant cells

cell plate