Cell Cycle and cell division- Biology CH. 7

What is the function of meiosis?

Reduce the chromosome number from diploid to haploid. Ensure that each haploid cell has a complete set of chromosomes. Generate diversity among the products.

What is precedent of meiosis I?

S phase during which DNA is replicated. Each chromosome then consist of two sister chromatids.

Cyclin-dependent kinases

catalyze phosphorylation of protiens that regulate the cell and are activated by binding to cyclin, which exposes the active site (allosteric regulation)

events of apoptosis

cell detaches from its neighbors, then DNA is cut into small fragments, next membranous lobes (blebs) form and break into fragments, in the end surrounding living cells usually ingest remains of the dead cell by phagocytosis.

The lifespan of an organism is linked to

cell reproduction or cell division.

where are chromatids held together at

centromere

G2

checkpoint is triggered by DNA damage

M

checkpoint is triggered by a chromosome that fails to attach to the spindle

meiosis

consist of two nuclear divisions that reduce the number of chromosomes to the haploid number. Produces four daughter cells

Trisomy

containing an extra of one chromosome

Translocation

crossing over between non-homologous chromosomes in meiosis I. locaction of genes relative to other DNA sequences is important, and trasnlocations can have profound effects on gene expression.

Shuffling of genetic material during meiosis occurs by two processes

crossing over- in prophase I homologous chromosomes (synapsis) and the four chromatids form a tetrad, or bivalent. The homologs seem to repel each other at the centromeres but remain attached at chiasmata. Genetic material is exchanged between nonsister chromatids at the chiasmate.

Are the daughter cells after mitosis haploid or diploid?

diploid

when do chromosomes condense?

during prophase

homologous chromosome

a chromosome pair that contains corresponding but not identical genetic information. For example, a homologous pair of chromosomes in a plant may carry different versions of a gene that controls seed shape. One may contain genes for a wrinkled seed and the other a smooth seed.

chromosome

a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

how do single-celled organisms usually reproduce themselves?

binary fission

somatic cells

body cells that do not specialize in reproduction

describe CDK activation

each CDK has a cyclin to activate it, which is made only at the right time. After the CDK acts, the cyclin is broken down by a protease. Synthesis and breakdown of cyclin is important in controlling the cell cycle. Cyclins are synthesized in response to various signals, such as growth factors

chromatid

each of the two threadlike strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.

Interphase in eukaryotes

follows M phase. When the cell nucleus is visible and typical cell functions occur, including DNA replication in cells that are preparing to divide.

spindle fiber

form a protein structure that divides the genetic material in a cell. The spindle is necessary to equally divide the chromosomes in a parental cell into two daughter cells during both types of nuclear division: mitosis and meiosis.

sexual reproduction

fusion of gametes ( gametes formed by meiosis)

apoptosis

genetically programmed cell death. two possible reasons - the cell is no longer needed (ex. the connective tissue between the fingers of a fetus). - old cells are prone to genetic damage that can lead to cancer (especially true of epithelial cells that die after days or weeks)

As a cell doubles in length, what happens to its surface area?

grows 4 times larger

As a cell doubles in length, what happens to its volume?

grows 8 times larger

Meiosis I

homologous chromosomes come together and line up along their entire lengths. The homologous chromosome pairs separate, but individual chromosomes made up of two chromatids remain together

nondisjunction

homologous pair fails to separate anaphase I. Sister chromatids fail to separate at anaphase II. results in aneuploidy

caspases

hydrolyze target proteins in a cascade of events

programmed cell death is controlled by signals-

internal signals may be linked to cell age or damaged DNA. Both internal and external signals lead to activation of caspases. The cell dies as caspases hydrolyze proteins of the nuclear envelope, nucleosomes, and cell membrane

Sexual reproduction

involves the fusion of gametes. results in offspring with genetic variation, gametes form by meoisis

G1 checkpoint

is triggered by DNA damage

S checkpoint

is triggered by incomplete replication of DNA damage

monosomy

missing a chromosome

How do single celled eukaryotes reprodcuce?

mitosis and cytokineses

M phases in eukaryotes

mitosis and cytokinesis

Aneuploidy

most human embyros from aneuploid zygotes do not survive. Many miscarriages are due to this.

genetic variations are due to

mutations

cell die in one of two ways

necrosis and apoptosis

Meiosis II

not preceded by DNA replication, sister chromatids separate, end result- four haploid cells that are not genetically identical

What is crossing over and when does it occur?

occurs in late prophase I-Prometaphase. The chromosomes within their homologous pairs coil and shorten. The chiasmata reflect crossing over, the exchange of genetic material between nonsister chromatids in a homologous pair. In prometaphase the nuclear envelope breaks down.

polyploidy

occurs thoough an extra round of DNA replication before meiosis, or lack of spindle formation in meiosis II. Polyploidy occurs naturally in some species and can be desirable in plants.

two proteins that regulate cell cycle

oncogene proteins and tumor suppressors

homologous pairs contain

one chromosome from the female parents and one from the male parents and have corresponding genetic information

Gametes only contain --- of chromomes with --- from each pair

one set of chromosomes. one homolog from each piar

hypersenstive response

plants use apoptosis in the hypersensitive response. They protect themselves from disease by undergoing apoptosis at the site of infection by a fungus or bacterium, preventing spread to other parts of the plant.

Are the chromosomes from #18 replicated or non-replicated?

replicated

Four events in cell division

reproductive signals initiate cell division, DNA replication, DNA segregation distribution of DNA into the two new cells, Cytokinesis- division of the cytoplasm and separation of the two new cells

Sexual reproduction results in

shuffling of genetic information in a population, no two indivials have exactly the same genetic makeup

What three structures appear during prophase?

spindles, condensed chromosomes, and reoriented centrosomes.

chemotherapy drugs stop cell division by

targeting cell cycle events

cytokinesis

the actual division of the cell and its contents into two in cell division. division of the cytoplasm

prophase of mitosis

the appearance of the nucleus changes as the cell enter prophase. the chromosomes become more condensed and coiled. the centrosome move to opposite poles

necrosis

the cell is damaged or starved for oxygen or nutrients. The cell swells and bursts/ Cell contents are released to the extracellular environment and can cause inflammation.

anaphase

the chromatids separate, and the daughter chromosomes move away from each other toward the poles

metaphase

the chromosomes line up at the midlines of the cell (the equatorial position)

How do the daughter cells that result from meiosis I differ from those that result from meiosis II?

the daughter cells of meiosis I contain the haploid number of replicated chromosomes. In the end of meiosis II the daughter cells contain the haploid number of unreplicated chromosomes.

chromatin

the material of which the chromosomes of organisms other than bacteria (i.e., eukaryotes) are composed. It consists of protein, RNA, and DNA.

haplontic life cycle

the mature organism is haploid and the zygote is the only diploid stage. Found in most protists, fungi, and some green algae.

prometaphase

the nuclear envelope breaks down and the compacted chromosomes, each consistingof two chromatids, attach to the kinetochore microtubules

diploid

the number that represents the total number of chromosomes in a cell in which each have a homologous pair.

clones

the offspring of asexual reproduction

diplontic life cycle

the organism is diploid and the gametes are the only haploid stage. Found in animals, brown algae, and some fungi.

alternation of generations

the organism passes through haploid and diploid stages that are both multicellular. Found in most plants and some fungi

what do the positions of the centrosomes determine?

the plane at which the cell divides. therefore, they determine the spatial relationship between the two new cell

centromere

the point on a chromosome by which it is attached to a spindle fiber during cell division.

mitosis

the set of processes in which the chromosomes become condensed and then segregate into two new nuclei. division of the nucleus.

What is the function of mitosis?

to conserve chromosome number and ensure each cell is identical to the parent.

At the end of meiosis I....

two nuclei form, each with half the original chromosomes (one from each homologous pair).The centromeres did not separate so each chromosome is still two sister chromatids

Each somatic cell contains ---- of chromosomes that occur in-----

two sets of chromosomes that occur in homologous pairs

during fertilization two haploid gametes fuse to form a zygote. Are zygotes haploid or diploid?

Diploid the number of chromosomes in a zygote=2n

when does the spindle form?

During prophase and prometaphase when the nuclear envelope breaks down.

cells in anaphase of mitosis vs. anaphase I and anaphase II

In anaphase in mitosis two identical replicated chromosomes are being pulling at their centromeres. In anaphase I the tetrads are being pulled apart. In anaphase II the replicated but not identical chromatids are being pulled apart.

Why is mitosis described as conservation division and meiosis described as reduction division?

Meiotic division reduces the chromosome number to the haploid number. In mitosis the number of chromosomes is conserved and both daughter cells contain the diploid number of chromosomes.

The essence of sexual reproduction is

- random selection of the diploid chromosomes set to form a haploid gamete -followed by fusion of haploid gametes from separate parents to make a diploid cell

describe the events of binary fission

1. DNA replication begins at the origin of replication at the center of the cell. 2. The chromosomal DNA replicates as the cell grows 3. The daughter DNAs separate, led by the region including ori. The cell begins to divide 4. Cytokinesis is complete; two new cells are formed

Sexual life cycles involve meiosis by two ways

1. Gametes may develop immediately after meiosis 2. Or each haploid cell may develop into a haploid organism (haploid stage of the life cycle) that eventually produces gametes by mitosis

The same cell goes through mitosis. How many chromosomes do each of the daughter cells have?

24 nonreplicated chromosomes

A different cell in the same organism ( diploid number is 24) is about to begin meiosis. How many chromosomes does this cell contain?

24 replicated chromosomes

A diploid cell with 24 chromosomes has just completed mitosis. After the S phase of interphase, how many chromosomes does this cell have?

24 replicated chromosomes

A cell in a human ovary is about to begin meiosis. How Many chromosomes does this cell contain?

46 replicated

Cell cycle checkpoint

CDK's function at cell-cycle checkpoints. G1, S, G2, and M

What events happen during interphase?

Consist of three subphases called G1, S and G2. The G1 phase is quite variable and a cell may spend a lot of time here carrying out its specialized functions. DNA is replicated in the S phase (synthesis). During the G2 phase the cell prepares for mitosis by synthesizing microtubules that will move the segregating chromosomes to opposite ends of the dividing cells.

What does crossing over result in?

Crossing over results in recombinant chromatids and increases genetic variability of the products.

are gametes haploid or diploid?

HAPLOID. the number of chromosomes =N

haploid

Half the diploid number of chromosomes are present in a cell. The cells do not have homologous pairs.

How does HPV result in uncontrolled cell reproduction?

Human Papilloma virus (HPV) stimulates the cell cycle when it infects the cervix.

How does cytokinesis in animal cells differ from that in plant cells?

In animal cells cytokinesis usually begins with a furrowing of the cell membrane, as if an invisible thread were cinching the cytoplasm between the two nuclei. The ring is composed of microfilaments such as actin and myosin that form on the cytoplasmic surface of the cell membrane. In plant cells the cytoplasm divides differently because there is a cell wall. as the spindle breaks down after mitosis, vessicles derived from the golgi apparatus appear along the plane of cell division, roughly midway between the two daughter nuclei. The vessicles are propelled along microtubules by the motor protein kinesin and fuse to form a new cell membrane. Then they contribute their contents to a cell plate to start a cell wall.

cells in metaphase of mitosis vs. metaphase I and metaphase II

In metaphase of mitosis the replicated chromosomes attach to spindles and line up across the middle of the cell. In metaphase I the homologous chromosomes form tetrads in the center of the cell. In metaphase II the chromosomes are lined in the center of the cell. The chromosomes are replicated but they are not identical. They are in a haploid cell.

As any cell grows,, what happens to its SA:VOL?

It gets smaller

Why is a larger SA:VOL advantageous to a cell?

The cell can transport materials in and out of the cell easier

leukemia can be formed by

a translocation that occurs in humans between chromosomes 9 and 22.

Aneuploidy

abnormal number of chromosomes

centrosome

an organelle near the nucleus of a cell that contains the centrioles (in animal cells) and from which the spindle fibers develop in cell division.

when do sister chromatids separate in mitosis

anaphase

oncogene proteins

are mutated positive regulators of the cell cycle- cancer cells they are overactive or present in excess. Receive signals that help regulate the cell cycle and insure that cell is ready to divide.

tumor suppressors

are negative regulators of the cell cycles, but are inactive in cancer cells. Example- RB blocks the cell cycle at R. HPV causes synthesis of E7 protein which fits into the protein-binding site of RB, thereby inactivating it. Produce proteins that signal cells when they are getting too crowded and program cell death when the cell is getting worn out.

basic strategies of reproduction-

asexual and sexual reproduction

Independent assortment

at anaphase I it is a matter of chance which member of a homologous pair goes to which daughter cell. The greater the number of chromosomes, the greater the potential for genetic diversity.