bio exam 3

Cell division occurs for

Growth

• Cell replacement

• Healing

• Reproduction - prokaryotes

cell division in prokaryotes

1. dna copied

2. cell elongates and chromosomes separates

3. ring separates new daughter cells

the ring that separates the 2 cells is similar to ___

microtubules

binary fission

cell spilts in half

eukaryotes have __ chromosomes (a shape)

linear

how many chromosomes do humans have

46

is eukaryotic cell growth controlled or no

very tightly controlled in comparison to prokaryotes who divide constantly

cell cycle in eukaryotes

G0: cells not dividing

G1: growth

S phase: DNA is copied

G2: Cell checks the DNA and grows

M: mitosis and cytokinesis

bases of dna are held together by

hydrogen bonds

G-C pairs are more/less resistant to denaturation than A-T pairs

more

Semi-conservative model of DNA replication

Template strand is read in the _____

direction

3’->5

New strand is built in the ____direction

5’-> 3’

Energy to build the DNA strand comes from

the hydrolysis of the nucleotide phosphates

The enzyme that adds nucleotides is

DNA

polymerase

true or false: DNA polymerase always works by adding a

new nucleotide to an existing one – it can’t start a new strand

true

DNA is unwound to create a

replication fork.

Synthesis is begun by

RNA

polymerase (primase) creating a primer

RNA primase

binds to the 5’ end of the template strand and starts synthesis then falls off

in depth steps of DNA replication

1. RNA primase lays down an RNA primer

2. DNA polymerase III extends the RNA primer in okazaki fragments

3. DNA polymerase I removes the primer and replaces it with DNA

4. DNA ligase forms a bond joining the DNA fragments

exonuclease

An exonuclease is an enzyme that removes nucleotides one at a time from the end of a DNA or RNA strand

leading v.s lagging strands

dna polymerase is following 3’ to 5’

unwinds the

parental DNA strands.

helicase

relieves the stress of

unwinding

Topoisomerase II (jump rope example)

Single-strand binding protein

stabilizes single strands of DNA

Prokaryotic cells produce daughter cells by

binary fission

Binary fission begins with

DNA replication

Replication is initiated at a specific location on the circular DNA molecule, called the

origin of replication,

FtsZ

encodes a protein that forms a ring at the site of constriction where the new cell wall forms between the two daughter cells

FtsZ is present in the genomes of diverse bacteria and archaea, suggesting that it plays a fundamental role in binary fission

mitosis def

In eukaryotic cells, the division of the nucleus, in which the chromosomes are separated into two nuclei.

cytokinesis def

In eukaryotic cells, the division of the cytoplasm into two separate cells.

what happens first, mitosis or cytokinesis?

mitosis

the name for mitosis and cytokinesis

mitotic cell division

chromosomes

A cellular structure containing the genetic material, consisting of a single DNA molecule with associated proteins.

chromosomes in prokaryotes

organized as a single, relatively small, circular chromosome.

chromosomes in eukaryotes

much larger and is organized into one or more linear chromosomes

The DNA of prokaryotes is attached to

the inside of the cell membrane

the DNA of eukaryotes is located in

the nucleus

experiments have strongly suggested that mitosis evolved from

binary fission

2 phases of the cell cycle

interphase and M phase

M phase

when mitosis and cytokinesis happen

interphase

the cell makes many preparations for division. These preparations include DNA replication and cell growth.

3 phases of interphase

s phase, G1 phase, G2 phase,

S phase

The phase of interphase in which the entire DNA content of the nucleus is replicated

G1 phase

The gap phase of the cell cycle between M phase and S phase in which the size and protein content of the cell increase and regulatory proteins are made and activated in preparation for S-phase DNA synthesis.

growth

G2 phase

The gap phase of the cell cycle between S phase and M phase in which the size and protein content of the cell increase in preparation for M-phase mitosis and cytokinesis.

G0 phase

nothing is happening

replication fork

The site where the parental DNA strands separate as the DNA duplex unwinds.

template strand

In DNA replication, the parental strand whose sequence is used to synthesize a complementary daughter strand. In transcription, the DNA strand whose sequence is used to synthesize a complementary mRNA molecule. The template strand is also called the noncoding, antisense, and minus strand.

semiconservative replication

after replication, each new DNA molecule consists of one strand that was originally part of the parental molecule and one newly synthesized strand.

single strand bonding protein

A protein that binds single-stranded nucleic acids to prevent the template strands from comin back together

2 types of topoisomerase

type 1 ; cut one strand of DNA

type 2: cut both strands of DNA

RNA primase

synthesizes a short piece of RNA complementary to the DNA parental strand. Once the RNA primer has been synthesized, DNA polymerase takes over, adding successive DNA nucleotides to the 3’ end of the growing strand.

A second key property of DNA polymerase is that it can only add nucleotides to the____ end of another nucleotide

3’

the direction of DNA chain growth

5’ - 3’, this is because i has to be antiparallel to the 3’ end the DNA polymerase binds to

leading strand

A daughter strand that has its 3’ end pointed toward the replication fork, so as the parental double helix unwinds, this daughter strand can be synthesized as one long, continuous polymer.

lagging strand

5’ end is near the replication fork, but the strand cannot grow in that direction.

how does synthesis occur on the lagging strand

To enable synthesis of the top strand, the replication fork moving to the left creates a single-stranded region of parental DNA ranging in length from a few hundred to a few thousand nucleotides. Synthesis of the daughter strand is initiated on this single-stranded stretch of parental DNA with its 5’ end near the replication fork. Elongation of the new strand occurs at its 3’ end as usual, which means that the daughter strand grows in a direction away from the replication fork, not toward it.

okazaki fragments

fragments the lagging strand of DNA is built in

proofreading

DNA polymerase I and III can detect the mispairing and removes a bad nucleotide

Dna polymerase iii

main replication synthesis

dna polymerase i

the specialized cleaner once pol iii is done, pol i comes to remove the rna primer, removes okazaki frament primers

Dna replication in prokayotes

origin of replication

each point at which DNA synthesis is initiated

replication bubble

A region formed by the opening of a DNA duplex at an origin of replication, which has a replication fork at each end.

what happens when 2 replication bubbles come into contact with each other

they fuse to form one larger replication bubble

origins of replication in prokaryotes

a circular DNA molecule can/cannot be replicated completely

can

because it has no ends and the replication forks can move completely around the circle

at each round of DNA replication the ends become slightly longer/shorter

shorter

at the ends the leadin strand is able to replicate the whole template strand but the lagging strand isn’t, the last RNA primer on the lagging strand still needs to be removed.

when removed, a section of template DNA remains unreplicated, so in the next generation doesn’t have the uncoded DNA and continues to get shorter and shorter with more rounds of replication

what mechanisms solve the problem of the shortenin of DNA ends

Each end of a eukaryotic chromosome is capped by a repeating sequence called the telomere

in the chromosomes of humans and other vertebrates, it consists of the sequence 3’-GGGATT-5’ repeated over and over again in about 1500–3000 copies

The telomere is slightly shortened in each round of DNA replication but is quickly restored by telomerase

telomerase activity is fully active in

germ cells which produce egg and sperm cells.

and stem cells

is telomerase active in most cells in the body

no.

In these cells, the telomeres are nevertheless shortened by about 100 base pairs in each mitotic division.

human cells stop dividing when their chromosomes have telomeres with fewer than ___ copies of the telomere repeat

100 (supports theory for aging)

why does DNA need to be condensed into chromosomes

the length of DNA contained in the nucleus of an average eukaryotic cell is well beyond the diameter of a cell.

also to make sure it doesn’t tangle

karyotype

A standard arrangement of chromosomes, showing the number and shapes of the chromosomes representative of a species.

how many chromosomes do cells in the human body have? what about gametes?

46, 23

homologous chromosomes

Pairs of chromosomes, matching in size and appearance, that carry the same set of genes; one of each pair was received from the mother, the other from the father. (form an x)

the sex chromosomes

x y chromosomes

The number of complete sets of chromosomes in a cell is known as its

ploidy

A cell with one complete set of chromosomes is

haploid

A cell with two complete sets of chromosomes is

diploid

Some organisms, such as plants, have four (4n) or sometimes more complete sets of chromosomes. Such cells are

polypoid

centromere

middle of the x chromosome shape that keeps the sister chromatids together

what do you use to count chromosomes

count centromeres

chromosome condensation

the chromosomes condense and become visible in the nucleus

prophase

first stage of mitosis The stage of mitosis characterized by the appearance of visible chromosome

mitotic spindle

a structure that pulls the chromosomes to opposite ends of the dividing cell

they radiate from the centrosome

centrosome

structure that mitotic spindle fibers radiate from

prometaphase

the nuclear envelope breaks down and the microtubules of the mitotic spindle attach to chromosomes

kinetochores

Associated with the centromere of each chromosome are two protein complexes

one located on each side of the constriction

Each kinetochore is associated with one of the two sister chromatids and forms the site of attachment for a single spindle microtubule.

metaphase

Chromosomes align as a result of dynamic changes in the mitotic spindle.

think METAPHASE → M= middle

anaphase

Sister chromatids fully separate

The centromere holding a pair of sister chromatids together splits

The spindle microtubules attached to the kinetochores gradually shorten, pulling the newly separated chromosomes to the opposite poles of the cell.

telophase

Nuclear envelopes re-form around newly segregated chromosomes.

The microtubules of the mitotic spindle break down and disappear

As the nuclei become increasingly distinct in the cell, the chromosomes contained within them decondense, becoming less visible under a microscope.

cytokinesis

The parent cell divides into two daughter cells

In animal cells, this stage begins when actin filaments form a contractile ring, the ring contracts, pinching the cytoplasm of the cell and dividing it in two

contractile ring

structure that promotes the division of one cell into 2

the equivalent of a contractile ring in binary fission

FtsZ protein

what happens during cytokinesis for plant cells

plant cells form a cell plateinstead of a contractile ring

phragmoplast

In dividing plant cells, a structure formed by overlapping microtubules that guide vesicles containing cell wall components to the middle of the cell where the vesicles will coalesce to form the new wall (cell p late)between daughter cells

a cell may have to receive a ____ before it divides.

signal

Cyclin–CDK complexes control

Cyclin–CDK complexes control