dna strucutre

DNA structure ex 1

DNA structure ex 1

Rosalind Franklin

• tried deducing the structure of DNA through x-ray diffraction + produced the photographs

• found DNA is twisted and has a double helix structure (w/ nitrogenous bases stacked in the center)

Erwin Chargaff

• analyzed the percentage of adenine, thymine, guanine, cytosine in DNA w/ different organisms

Erwin Chargaff’s Rule

in organisms,

adenine = thymine (percentage)

cytosine = guanine (percentage)

Watson/Crick

• worked together to build a DNA model and use variations of the helix for their models (which was unsuccessful)

• Warson found adenine could form hydrogen bonds with thymine

Maurice Wilkins

• tried deducing the structure of DNA through x-ray diffraction

what are complementary base pairing?

specific bases bond to each other and revolves around DNA

• adenine & thymine

• guanine & cytosine

purines

2 rings (hydrogen bonds)

• adenine/guanine

pyrimidines

1 ring (hydrogen bond)

• thymine/cytosine

directionality of DNA

5’3 to 3’5 on one side vertically and flipped on the other

• directionality based on carbon atoms

• c4 into c5 is 5’

• c2 into c3 is 3’

what is the goal of DNA replication?

to make identical copies of your genes (interphase)

eukaryotes in dna replication

multiple origins

prokaryotes in dna replication

1 origin

what is the role of complementary base pairing in dna replication?

allows for the creation of daughter strands through complementary base pairing

topiomerase role

unwinds dna

helicase role

unzips dna

primase role

inserts temporary primers onto parent dna

dna polymerase role

builder, base pairs + builds new dna

nuclase role

removes temporary primers from dna

ligase role

glue, forms bonds between sugars/phosphates

topiomerase order in dna replication

1

helicase order in dna replication

2

primase order in dna replication

3

dna polymerase order in dna replication

4

nuclase order in dna replication

5

ligase order in dna replication

6

what is the difference between a leading and lagging strand?

lagging - discontinuous, lagging BEHIND

leading - continuous, ahead

leading v lagging strand

why is dna replication semi-conservative?

because it has one old strand and 1 new strand when dna is replicated (where dna polymerase then proofreads the new strand for mistakes)

what are the major parts of the cell cycle?

• G1

• S

• G2

• M

what is the order of the cell cycle and which are apart of interphase?

• G1, S, G2 (interphase, 1-3)

• M (4)

G1

• cell increase in size

• prepares to replicate it’s DNA

• cellular contents (excluding chromosomes are duplicated)

S

• cell replicates its dna so the cell now has 2 sets of chromosomes

• each of the 46 chromosomes are duplicated by the cell

G2

• cell continues growing and prepares to divide

• cell double checks the duplication of chromosomes for any errors

• makes any needed repairs/fixes

M

• cell stops growing and divides into 2 daughter cells (each have same # of chromosomes)

what makes up the m-phase from beginning to end?

• prophase

• metaphase

• anaphase

• telophase

• cytokinesis

phases of mitosis ex 1

phases of mitosis ex 2

interphase ex

prophase ex

metaphase ex

anaphase ex

telophase/cytokinesis ex

why do cells divide?

• to replace old, dead or damaged cells

• to grow the organism/cell

G1 checkpoint

• checks that there’s no DNA damage

• checks theres enough resources for the cell

S checkpoint

• checks for errors during DNA replication

G2 checkpoint

• checks to makes sure there’s no DNA w/ damage

• checks that chromosome sets are complete and that theres enough cell components

m checkpoint

• checks that all sister chromatids are attached to mitotic spindle

what happens if the cell cannot pass the checkpoint(s)?

• it may either go to G0 (if in G1) where it will pause and stay alive but not actively prepare to divide

• can also go through apoptosis (self destruct) if the cell is a danger to other cells

how is the cell cycle controlled?

• through internal/external regulators

• through CDKS/cyclins

internal regulators

• inside the cell, proteins that help the cells divide at a correct rate under the right conditions

external regulators

• signals from the outside of the cell that regulates the cell cycle based on environmental conditions and other factors

CDKs

enzymes that interact w/ cellular components related to the cell cycle

• usually present in the cell inactively + is only activated when it binds to cyclins

cyclins

proteins that are made and broken down at certain times during the cell cycle (levels rise and fall depending on where in the cell cycle)

• attaches to and activates CDKs

what happens after CDKs/Cylins bind together?

• shape of CDK changes, which signals that they are now active (active cyclin-CDK complex) which allows them to interact w/ specific molecules in the cell and allow the cycle to keep going

what are MPFs?

a cyclin/CDK complex made up of cyclin B and CDK1

• regulates the entry from G2 to M phase

• MPF activity decrease towards the end of mitosis b/c of the break down of cyclin B

cyclin/cdk concentration through cell cycle

what is the role of p53 in the cell cyle?

• it prevents mutations that are in some DNA from being passed to daughter cells

what happens if there is a loss of control of the cell cycle?

• possible spread of cancer cells b/c there is no checkpoints/regulators within the cell

• if there is a rapid dividing of cells, then it it more likely for there to be cancer cells which will spread