Chapter 3 Flashcards
What are the types of cell division?
2 types, mitosis and meiosis
Mitosis :
It produces :
The growth and repair of body cells
-2 genetically identical daughter cells w/ the same chromosome number as the parent cell
(mitosis) Each daughter cell is
Diploid (2n), just like its parent cell
Meiosis
Each resulting cell:
- Occurs on in sexually reproducing organisms
- it produces gametes (sperm and ova) w/ ½ the chromosome number of the parent cell
- Is haploid (n)
Chromosome consists of
A highly coiled and condensed strand of DNA
A replicated chromosome consists of
2 sister chromatids, where 1 is an exact copy of the other
Centromere
A specialized region that holds the 2 sister chromatids together
Spindle fibers connect the
Centromere to the centrosome during cell division
Each chromosome contains
2 identical chromatids connected at a centromere
Cell cycle
When living and dividing cells pass through a regular sequence of growth and division
Stem cells (from human embryos)
- Retain the ability to divide indefinitely
2. to differentiate into any cell type
Cell cycle is strictly regulated by many
Proteins including some called cyclins
Some proteins are internal regulators making sure
That the cell does not undergo mitosis until certain conditions are met
Other proteins such as growth factors are
External regulators of the cell cyle: speeding up, slowing it down, or even stopping it
Cell cycle consists of
To move from one phase to the next
5 stages: G1 , S, G2, mitosis, cytokinesis
The cell must pass through 3 checkpoints
G1
Newly divided cell enters this phase right after completing mitosis
During G1, the cell
- Increases in size
2. prepares to replicate it’s DNA
G-1 checkpoint
If the cell is: - healthy - contains adequate resources - DNA is undamaged, growth factors stimulate the cell to proceed to DNA synthesis of S phase
If the cell doesn’t pass G1-checkpoint, the cell
Dies or enters a resting state, G0 phase
S-phase
DNA is synthesized through the process of replication
S-checkpoint
DNA synthesis is monitored for any replication errors
S-phase checkpoint: If the synthesis progresses without errors
Growth signals will stimulate the cell to proceed to G2
G-2
Cell has to produce organelles and other cellular components that will populate two new functional daughter cells
G-2 checkpoint
All chromosomes must be
1. fully replicated
2.contain no other types of damage
only then can the cell enter M phase
When errors occur in cell division, it causes the
Development of cancer
More than ____% of life of a cell is spent in _______.
90%, interphase
Most cells observed under a microscope are
In interphase
During interphase, chromosomes
Replicate in preparation for cell division
During interphase, 1 or more nucleoli become visible within the nucleus and
The nuclear membrane remains intact
Interphase is made up of
G1, S, G2
Mitosis is
Actual division of the nucleus
Mitosis is divided into 4 phases
Prophase, metaphase, anaphase, and telophase
Prophase
- Strands of chromosomes begin to condense and become visible
- Nucleoli disappear
- Spindle fibers begin to form in the cytoplasm extending from 1 centrosome to the other
- centrioles begin to migrate to the poles,
- nuclear membrane begins to disintegrate
Metaphase
- Chromosomes line up single file located on the equator or (metaphase plate)
- centrosomes are at opposite poles of the cell
- spindle fibers run from centrosomes to the centromeres of the chromosomes
Anaphase
- Centromeres of each chromosome separate and spindle fibers begin to pull the sister chromosomes apart
- anaphase is the shortest phase of mitosis
Telophase
- Chromosomes cluster at opposite ends of the cell and the nuclear membrane reforms
- supercoiled chromosomes begin to unravel and tor return to their pre-cell division condition as long , threadlike strands
- the nuclear membrane reforms
Cytokinesis
Division of the cytoplasm
In animal cells, a cleavage furrow forms
Down the middle of the cell as the cytoplasm pinches inward and the 2 daughter cells separate from each other
In plant cells, a cell plate forms down
The middle of the cell
Daughter cells do not
Separate from each other ,instead a sticky middle lamella cement adjacent cells together
Meiosis
A form of cell division in which cells having the diploid chromosome number (2n) produce gametes (sex cells) with the haploid chromosome number (n)
Meiosis occurs in
2 stages, meiosis I and meiosis II
Meiosis I is also called
Reduction division
What occurs in meiosis I?
Synapsis and crossing-over
Synapsis
Chromosomes pair up precisely w/ their homologue so that crossing-over can occur
Crossing-over
The process in which homologous chromatids exchange genetic material, it ensures greater variety in the gametes
Homologous chromosomes separate, failure to separate is
Nondisjunction
Next, chromosomes line up randomly on the
Equatorial plate and separate independently
This means that how 1 pair of chromosomes lines up and separates
Has no effect on how any other pair of chromosomes lines up and separates
Each resulting gamete is
Genetically unique
Meiosis II
Sister chromatids separate
This division
Maintains the haploid number of chromosomes
This phase completes the goal of meiosis
Producing 4 genetically unique cells from 1 original mother cell
In metaphase I of meiosis I
In metaphase II of meiosis II
Chromosomes are lined up double files
Chromosomes are lined up single files
Summary:
Mitosis is for growth/repair and meiosis is for the production of gametes only
Summary of meiosis I and II
I: homologous pairs separate
II: sister chromatids separate
