Chapter 10 Flashcards
Prokaryotic cell division occurs as ______
binary fission
What is the genetic information in a prokaryote called?
Nucleoid
Where does copying begin in prokaryotes?
Replication origin
What direction does copying proceed in for prokaryotes?
Bi-directionally
Describe the process of binary fission
- Bacterial cell has an origin of replication
- Replication begins at origin and proceeds in opposite directions
- Replicated origins move to two ples of the cell as replication continues
- Plasma membrane grows inward, new cell wall is synthesized
- Cell cuts in two
How many chromosomes are in humans?
46 (23 nearly identical pairs)
How many chromosomes do eukaryotes tend to have?
10-50
What are the three parts of a cell’s life cycle?
Cell growth, including DNA replication
Nuclear division/mitosis
Division of the cytoplasm in cytokinesis
What is mitosis?
DNA is equally and precisely divided, generating daughter cells that are genetic copies of the parent cells. This occurs with almost perfect fidelity and is facilitated by the mitotic cytoskeleton.
What is meiosis?
Daughter nuclei with half the number of chromosomes are produced; the arrangement of genes on chromosomes are different from parent cells
What are chromosomes?
Linear DNA molecules combined with proteins.
The complex of DNA and all its proteins is called ____
Chromatin
What proteins pack DNA into a shorter length?
Histone proteins
What is the structure of a nucleosome?
An 8-protein nucelosome core particle forms when DNA winds around 2 molecules each of H2A, H2B, H3, and H4
What segment connects nucleosomes?
A linker segment
What is the 10-nm chromatin fiber?
Compacts DNA by a factor about 7
30-nm chromatin fiber
Forms when Histone H1 attaches, which causes the structure to coil
Complex of DNA and all associated proteins is called
Chromatin
What is the solenoid model?
It predicts that the nucleosomes spiral helically with about six nucleosomes per turn
Euchromatin vs heterochromatin
Euchromatin is more loosely packed and more highly expressed in comparison to heterochromatin regions
What are sister chromatids?
Replicated chromosomes connected to eachother at the centromere- held together via sister chromatid adhesion (cohesion) until mitosis separates them
What holds sister chromatids together?
Cohesin
The equal distribution of chromosomes into each of two daughter nuclei is called
Chromosome segregation
What is the difference between sister chromatids and homologous chromosomes?
Sister chromatids are identical, homologous chromosomes code for same genes but have different alleles
What is ploidy?
The number of chromosome sets in a cell or species
If an organism has only one copy of each chromosome type, it is a ____
haploid
Most eukaryotes have two copies of each type of chromosome, making them
Diploids
What is polyploidy?
When species have 3 or more of each type od chromosome
The two chromosomes of each pair in a diploid cell are called homologous chromosomes because
One is from the mother, one is from the father, and they have the same genes in the same order
What does a karyotype show?
An individual’s array of chromosomes
How are cells prepared for a karyotype?
Sample is added to a culture medium that has a stimulator for growth and division of cells incubated at 37 C
Cell is stained so chromosomes are visible
Chromosomes are photographed
What are the steps of interphase?
G1 (primary growth, longest phase)
S (DNA replication)
G2 (organelles replicate, microtubules organize)
Eukaryotic cell cycle
Interphase (G1,S,G2), Mitosis, Cytokinesis
T or F: G1 varies in length
True
What is special about the G1 phase?
Here, many cells stop dividing and are instead put in a G0 phase, where some never resume the cell cycle
What happens in G1?
G1 is a period of growth where RNA, proteins, and molecules needed for S phase are created
S phase
DNA is replicated and copies are held together
G2 phase
No DNA synthesis, but protein and RNA synthesis continues to prepare for mitosis
How many hours spent in each stage?
G1- 10 hrs
S- 9 hrs
G2- 4 hrs
Mitosis- 1 hr
What are the checkpoints in the cell cycle?
G1/S
G2/M
Mitotic spindle checkpoint
Mitosis divided into 5 phases
Prophase
Prometaphase
Metaphase
Anaphase
Telophase/cytokinesis
Mitosis requires the formation of
a spindle
Centrosome
The main microtubule organizing center of animal cells and protists
What happens to the centrosome in mitosis
Centrosome has centrioles that are duplicated and divided
Microtubles extending from the centrosomes produce
Arrays/asters at the tips that form the poles of the spindle
What is the spindle
Separated centrosomes and the mass of microtubules in between them
G1
Chromosomes are unreplicated and extend through nucleus
S
DNA replication
G2
DNA condensation using cohesins which align the sister chromatids tightly- centriole has also doubled
Prophase
Individual condensed chromosomes first become visible
Condensation continues
Spindle apparatus assembles and centrosomes move to opposite poles, generating the spindle as they separate
Nuclear envelope starts to disintegrate and nucleolus disappears
Prometaphase
Transition occurs after disassembly of nuclear envelope
Spindle microtubules grow from centrosomes at opposite spindle poles towards the center of the cell
A kinetochore forms on each sister chromatid at the centromere
Kinetochore microtubules bind to kinetochores
Nonkinetochore microtubules from opposite sides overlap at the spindle point
Chromosomes begin to move to center of cell in a process called congression (facilitated by motor proteins at kinetochores and assembly/disassembly of microtubules)
Metaphase
Spindle microtubules move chromosomes into alignment at the spindle midpoint/metaphase plate
Condensation gives each chromosome a characteristic shape
Karyotypes formed here according to size and shape
Anaphase
Centromeres split, cohesin protein is removed from all chromosomes
Sister chromosomes pulled to opposite sides (microtubules shorten)
Separase enzyme
Anaphase A
Motor proteins at the spindle poles pull kinetochore microtubules polewards, and the microtubule disassembles into tubulin subunits
Anaphase B
Nonkinetochore microtubules elongate the cell as motor proteins walk in opposite directions- grow in length as they slide along
Telophase
Spindle apparatus disappears, chromosomes decondense, returning to extended state, muclear envelope forms around cromosomes which uncoil, nucleolus reappears and RNA transcription resumes
Cytokinesis
Animals, protists, fungi: a furrow/contractile ring of microfilaments slide together girdles the cell and deepens until it cuts the cytoplasm into two
Plants: cell plate forms and grows laterally until cytoplasm divides in two
T or F: mitosis occurs within the nucleus in some organisms
T, fungi and protists
What determines the plane of cytoplasmic division
Microtubules at spindle midpoint
What is the contractile ring made from
Actin and myosin
Cytokinesis in plant cells
- Vesicles with material collect in the plane
- More vesicles added and fuse togehter, dumping contents into an expanding wall which separates cell into two by a continuous wall
What is cell division?
One cell divides to form two new cells- daughter cells
What kinds of processes happen within cells before they divide?
Growth period- protein synthesis, cell growth, ER synthesizes phospholipids and membrane proteins and the ER increases in surface area, and other organelles grow or become more numerous
Afterwards, DNA replication occurs, followed by mitosis
What does cenocytic mean?
Many nuclei are interspersed throughout cytoplasm- cytokinesis does not occur
How is eukaryotic dna stored?
Linear chromosomes containing a single DNA molecule with 2 strands of DNA
How many nucelotides in an eukaryotic chromosome?
1 million- some human chromosomes are over 100 million nucleotides long
Chromatin
A dna protein complex
what are histones?
a class of small dna proteins that bind dna
nucleosome
the complex of dna and histones
nucleosome core particles
the histones that the dna wraps around
What are the five types of histones?
H1, H2A, H2B, H3, and H4
what histones make up the nucleosome core particle?
h2a, h2b, h3, h4 (2 molecules each to make an 8-protein complex)
how many base pairs of dna in a nucleosome?
150 base pairs
what is a linker?
a short segment of about 50 dna base pairs that extends between one nucleosome and the next
10 nm chromatin fiber
a series of nucleosomes connected by linkers- is about 7 times shorter than dna
H1 histone
one H1 molecule binds both to the nucleosome and to the linker dna, causing the nucleosomes to form a coiled 30 nm structure called the 30 nm chromatin fiber, which has about 6 nucleosomes per turn
solenoid model
6 nucleosomes coiled together to form the h1 protein- this is the chhromosome in the metaphase stage of the cell in mitosis (the most compact form of a chromosome)
what do chromosomes look like in cells not in mitosis?
chromatin fibers are loosely packed in some regions and densely packed in others
euchromatin
loosely packed region
heterochromatin
densely packed region
nonhistone proteins
proteins other than chromatin needed for higher level coiling of chromatin
condensins
a nonhistone protein that binds dna at two sites and holds together two parts of a chromosome positioned next to eachother
topoisomerase
adjusts the twisting of the two strands of dna which causes the dna to form loops
The two identical copies of each chromosome that are produced in DNA replication are called
sister chromatids
how are sister chromatids held together?
sister chromatid cohesion- ring-shaped proteins called cohesins circle the sister chromatids along their length
how many chromosomes in a human egg cell?
23
for each of the 23 chromosomes in an egg cell, there is a ______ in the sperm cell
homologous chromosome
what is a diploid?
cells that contain homologous pairs of chromosomes
what are haploids?
only have one homolog for each chromosome
what is the ploidy of human cells?
2n=46
G1
period of growth before the dna replicates, the cell synthesizes proteins, rna, and molegules
s phase
cell duplicates chromosomes, chromosomal proteins
g2
continued synthesis of dna molecules and rna molecules, and it continues to grow
which is the phase that usually varies in length?
g1
how long do s and g2 phases last?
10-12 hours for s and 4-6 for g2 and 1 hour or less for mitosis
what is the g0 phase?
A phase where cells not destined to divide enter- cell performs normal functions but stops growing and does not replicate its dna- for example, organs and neurons
what is the centromere?
a specialized chromosomal region that connects sister chromatids and attaches them to the mitotic spindle
when do the centrosomes first separate?
s phase
what is an aster?
radiating array produced by microtubules
spindle poles
centrosomes at either end
what is the kinetochore?
a structure consisting of proteins attached to the centromere that mediates attachment and movement of chromosomes along the mitotic spindle
describe the orientation of a sucessfully attached chromosome
attached to microtubules extending from each spindle pole
nonkinetochore microtubules
overlap those from the opposite spindle pole
metaphase plate
the midpoint where chromosomes align
what enzyme is activated during anaphase
separase
furrow
girdles the cell and deepens until it cuts the cytoplasm in two
cell plate
a new cell wall that forms between the daughter nuclei until it divides the nuclei in two - formed by vesicles containing cell wall material
describe gorbsky’s experiment
bleached region of kinetochore microtubule remained the same length, indicating that the bleached region remained the same distance from the pole as the chromosomes moved toward the pole- microtubule disassembles as kinetochore walks over it
why does a dividing cell elongate?
- motor proteins on overlapping protein nonkinetochore microtubules walk in opposite directions, reducing the amount of overlap present, which pushes the spindle poles further apart.
- the nonkinetochore microtubules push the poles apart by growing in length as they slide along
why is yeast an ideal organism to study?
single celled and easy to manipulate- rapidly reproduces
key checkpoints in a cell
g1/s, g2/m, mitotic spindle
what does the g1/s cdk do?
phosphorylates target proteins for g1/s transition and commits cell to dna replication
s-phase cdk
phosphorylates target proteins for initiation of dna replication and progession through s
mitotic cyclin/m cdk
phosphorylates proteins for g2/m transition and progression through mitosis
most important checkpoint in a cell
g1/s checkpoint, because once the cell replicates its dna, it is committed to completing the rest of the cell cycle
what is the major determinant of whether cell is ready to divide?
cell size, so growth factors are an important molecule present in cell growth
cells with more chromosomes tend to grow ______ before cell division
larger
contact inhibition
inhibition of movement or proliferation of normal cells that result from cell-cell contact - shunts cell into the g0 phase
g2/m checkpoint
determines whether cell is ready to begin mitosis- senses errors in dna replication, inhibits passage through g2/m
mitotic spindle checkpoint
assesses whether chromosomes are all attached properly to the mitotic spindle- marks transition from metaphase to anaphase- senses the absense of tension in the cohesion rings
g1 cyclins
bind to g1 cdks before the g1/s transition to increase expression of the gi/s and s cyclins. g1 cyclins do not change rapidly at cell cycle transitions and instead are activated by signal transduction pathways.
g1/s cyclins
bind to gi/s cdks to form complexes that increase expression of s cyclins- facilitate the transition from g1 to s
s-phase cyclins
bind to s-phase cdks to activate dna replication
mitotic cyclins
bind to mitotic cdks in g2 to form a complex that is required for the transition from g2 to m and progression of the cell through mitosis. also known as the m phase promoting factor, which activates the anaphase promoting complex
anaphase promoting complex (apc)
degrades an inhibitor of anaphase, leading to separation of sister chromatids
describe the unique cell division properties of cancer cells
divide continuously and uncontrollably, producing a tumor, and in metastasis, they break loose and grow into new tumors in other body regionss. many of their proteins code for components of the cyclin/cdk system, and others regulate gene expression or receptors. oncogenes encode altered versions of these products.
what is the structure of dna in a proakaryote?
one circular chromosome packed and coiled into an irregularly shaped mass called the nucleoid. many bacterial cells also contain plasmids which are circular dna molecules
how long does it take for the cell cycle in prokaryotes
about 20 minutes
describe the process of dna replication in bacteria
- replication starts at the ori
- proceeds in opposite directions
- the two replicated origins migrate to the two ends of the poles as replication continues
- replication is complete and a new cell wall is synthesized
T or F: mitosis evolved from binary fission
T
