BIO UNIT 4: The Cell Cycle, Mitosis, and Meiosis

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What is the cell doctrine?

The idea that all cells arise from preexisting cells.

1. Why do cells reproduce?
2. The more specialized a cell becomes, the (more/less) likely it is to remain capable of reproducing itself.

1. To grow and develop or to replace dead or damaged cells.
2. Less.

What happens during cell division?

1. A dividing cell precisely replicates its DNA
2. Allocations the 2 copies of DNA to opposite ends of the cell.
3. Separates into two daughter cells containing identical information.

What are the characteristics of chromosomes?

1. Supercoils of chromatin
2. They are a single, long, double-stranded molecule of DNA - segments are called genes.
3. Various proteins service to maintain chromosome structure
4. They exist in precise #s depending on the species. Eg. Humans have 46 and gamete celles (sperm or ova) have 23.

1. What do chromosomes look like during interphase?
2. What happens in this phase?

1. They are loosely folded and cannot be seen with a microscope.
2.

What do chromosomes look like during the mitotic phase?

Highly folded and condensed and can be seen with a microscope.

What generally happens in preparation for EU cell division?

1. Complete genome is duplicated.
2. This results in identical copies of the chromosome's DNA and are initially attached to each other at the centromere.

1. What is mitosis?
2. What generally happens during mitosis?

1. It is the equal division of one nucleus into two genetically identical nuclei.
2. Sister chromatids are pulled apart resulting in segregation of two sets of chromosomes (one at each end of the cell).

What generally happens during cytokinesis?

The process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells, each containing a single nucleus and one set of chromosomes.

1. What is the cell cycle?
2. It alternates between the _______ phase and the _________ phase.
3. Which two processes form the M phase?

1. Sequence of events in which a cell duplicates its contents and divides in two.
2. mitotic (M) phase (dividing phase) and interphase (non-dividing phase).
3. Mitosis and cytokinesis.

What happens during the mitotic (M) phase?

1. Mitosis (division of nucleus)
2. Cytokinesis (division of cytoplasm)
3. Interphase (non-dividing) a major part which includes most of a cell's growth. Happens in 3 parts:
a) G1 phase: 1st growth phase (G=Gap)
b) S phase: DNA is synthesized & chromosomes are duplicated to produce two sister chromatids
c) G2 phase: 2nd growth phase

1. What are the 4 phases of mitosis and meiosis?
2. What are the two main differences between mitosis and meiosis?

1. Prophase
Metaphase
Anaphase
Telophase
2. a) Replication of the genome is followed by one round of cell division in mitosis and 2 rounds of cell division in meiosis.
b) Recombination occurs in meiosis between homologous chromosomes.

Explain what happens during prophase.

1. In the nucleus:
a. Nucleoli disappear
b. Chromatin fibres condense into chromosomes composed of 2 identical chromatids joined @ the centromere.
2. In the cytoplasm:
a) Mitotic spindle forms. It's composed of microtubules between the two centrosomes.
b) Centrosomes move apart by lengthening of microtubule bundles between them.

What is a mitotic spindle?

1. A spindle-shaped structure that develops outside the nucleus during mitosis. These fibres pull the chromatids apart toward opposite poles.

What is the kinetochore?

The protein structure on chromosomes where the spindle fibers attach during cell division to pull the chromosomes apart.

Explain what happens during Anaphase.

1. Anaphase is characterized by movement. Begins when paired centromeres of each chromosome move apart.
2. Sister chromatids split into chromosomes and move toward opposite poles of the cell.
3. Kinetochore microtubules shorten at kinetochore end as chromosomes approach the poles.
4. The poles of a cell move apart, elongating the cell.

Explain what happens during telophase.

1. During Telophase: (a) Nonkinetochore microtubules further elongate the cell. (b) Daughter nuclei begin to form at the 2 poles.
(c) Nuclear envelopes form around the chromosomes from fragments of the parent cell's nucl. envelope & portions of endomembrane system. (d) Nucleoli reappear
(e) Chromatin fiber of each chromosome uncoils and chromosomes become less distinct.

What happens by the end of telophase?

1. Mitosis is complete.
2. Cytokinesis has begun and the appearance of two separate daughter cells occurs shortly after.

What is a nonkinetochore microtubule?

A microtubule that does not attach to a kinetochore on a centromere during mitosis.

1. Males carry ____ sex chromosomes and females carry ___ sex chromosomes.
2. Traits determined by genes on the X or Y chromosomes are called _______.

1. XY and XX
2 sex-linked traits

What is a genome?

The genome is the entirety of an organism's hereditary information.

Explain what happens in meiotic prophase 1.

1. The chromosomes condense and become visible. Nuclear envelope breaks down.
2. The centrioles form and move toward the poles
3. The nuclear membrane begins to dissolve
4. The homologs pair up, forming a tetrad
Each tetrad is comprised of four chromatids.
5. Homologous chromosomes will swap genetic material in a process known as crossing over (abbr. as XO). Crossing over increases genetic diversity by creating four unique chromatids.

Explain what happens in meiotic metaphase 1.

1. Microtubules grow from the centrioles and attach to the centromeres.
2. The tetrads line up along the cell equator

What happens during crossing over?

1. Genetic material from the homologous chromosomes is randomly swapped. This creates four unique chromatids
2. Since each chromatid is unique, the overall genetic diversity of the gametes is greatly increased.

Explain what happens in meiotic anaphase 1.

1. The centromeres break and homologous chromosomes separate & the sister chromatids stay together.
2. Cytokinesis begins: The 2 cells separate and prepare for meiosis 2.

Explain what happens in meiotic anaphase 2.

1. Sister chromatids separate and meiosis ends in 4 haploids cells from one diploid cell.

What is karyotype?

The display of an organisms genome. The cell is frozen in metaphase, and examined for abnormalities.

What must be available for exact replication to occur? (4 points)

1. The actual DNA - to act as a template
2. A pool of relevant enzymes to stimulate reaction.
3. A supply of the relevant enzymes to stimulate reaction
4. ATP to provide energy for these reactions

What happens during replication?

1. Double helix structure uncoils
2. Exposed nucleotides are available so that free nucleotides can pair up with them. Each is used as a template for synthesis of a new complementary strand.
3. Once paired up, they recoil into double helix - now 2 strands of DNA.

Why is replicated DNA referred to as semi-conservative?

B/c it possesses 50% of the original genetic material from its parent.

What enzymes are involved in DNA replication?

DNA helicase, single-stranded DNA binding proteins, RNA primase, DNA polymerase, and DNA ligase.

What does DNA helicase do?

Unwinds DNA at replication fork: Uses ATP, makes a single strand cut, and allows one strand to flow freely around the other. H-bonds are broken.

What do single-stranded DNA binding proteins (SSB proteins) do?

Binds to separated DNA strands to prevent base-pairing from coming back together.

What does RNA primase do?

Makes very short piece of RNA by base-pairing RNA nucleotides with template DNA.

***This has to happen b/c DNA polymerase III cannot start growing a chain from scratch.

What does DNA polymerase do? (2 points)

1. Adds new nucleotides at free 3' ends of growing chain using base-pairing rules to insert complementary nucleotides. It can keep adding indefinitely if there is no blockage.
2. Removes RNA primers, fills in gaps by base pairing, and inserts new DNA nucleotides to replace RNA primer

What does DNA ligase do?

Seal gaps where adjacent nucleotides on one strand have not been joined.

What is the leading strand of DNA?

The leading strand template is the strand of DNA being replicated continuously. It's the strand that goes from 3' to 5'. This is because will allow the strand to grow from 5' to 3'.

1. What is the lagging strand of DNA? (3 points)
2. What is it also known as?

1. * The lagging strand grows in the direction opposite to the movement of the growing fork and is synthesized discontinuously.
* It needs to be replicated in fragments because the Primase (that adds the RNA primer) has to wait until the fork opens to be able to put the primer in.
* It eventually joins together.
2. Ogasaki fragments.

How can mutations occur? (3 points)

1. Subsitution of the wrong base at a certain location
2. Breakage of DNA bonds so incorrect bases are inserted (due to chemicals)
3. Large sections of DNA or single bases deleted causing a misreading of the entire sequence

Cells often spend much more time _______ DNA than __________ it.

repairing vs synthesizing.

What happens during metaphase?

1. Nuclear envelope fragments and this allows microtubules to interact with chromosomes.
2. Spindle fibres (bundles or microtubules) extend from each pole toward the cell's equator.
3. Each chromatic now has a kinetochore, located in the centromere region.
4. Chromosomes move to the metaphase plate (equidistant between the spindle poles).

1. How many cells does mitosis produce? Are they the same?
2. How many cells does meiosis produce? Are they the same?

1. Mitosis produces two. They are identical.
2. Meiosis produces four. They are different.

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