Knowt for Chapman
Prokaryote Reproduction-Prokaryote DNA
In prokaryotes the chromosomes are simpler.
DNA in prokaryotes consists of one circular chromosome that is attached to the cell membrane.
Prokaryotic cells do not have a nucleus that contains their DNA.
Cell Division in Prokaryotes
Prokaryotes reproduce through a process called binary fission.
The DNA is copied and results in two identical chromosomes.
A new cell membrane begins to develop between the two DNA copies.
Binary Fission can occur as fast as 35 minutes to 11 hours.
Bacteria / Binary fission time 1.)E. coli / 0.35hr 2.)Bacillus subtilis / 0.43hr 3.)Clostridium botulinum / 0.58hr 4.)Anabaena cylindrica / 10.6hrs 5.)Chlorclla pyrenvidosa / 7.75hrs 6.)Acntha amoeba / 11hrs 7.)Paramaesium spp. / 10hrs 8.)Sachcharomyces / 2hrs
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Chromosomes
Chromosomes are rod-shaped structures made of DNA and protein.
the DNA strand is tightly coiled around a chunk of protein called a histone
Histones maintain the shape of the chromosome and help tightly pack the DNA.
A chromatid is an identical half that forms as DNA makes a copy of itself before the cell divides.
Chromosome Structure
Two chromatids of a chromosome are attached at a point called a centromere.
The centromere holds the chromosomes together until they separate during cell division.
In between cell division, parts of the chromosomes uncoil so they can be read and used to direct the activities of the cell. This uncoiled DNA is called chromatin.
Chromosome Numbers
Animal chromosomes are organized by size into sex chromosomes and autosomes.
Sex chromosomes determine the sex of the organisms. (they may carry other characteristics as well. (2 sex chromosomes)
The sex chromosome can either be X or Y.
You inherit one from each parent. XX- typical female, XY- typical male
All of the other chromosomes are called autosomes. (44 autosomes for humans)
Pair #’s 1-22 are the autosomes
Chromosome Number
Every sexually reproducing organism has two copies of each autosome (one from each parent).
The two copies of each autosome is called a homologous chromosome pair or homologues.
Typical humans have 46 total chromosomes (44 autosomes+ 2 sex chromosomes)
The picture is of a karyotype- a photomicrograph of the chromosomes in a normally dividing human cell.
Homologous Chromosomes
Diploid vs Haploid
Somatic Cells (body cells) are cells that have two homologous chromosomes and are called diploid. (di=two)
Every cell in your body except sperm and egg cells.
Also referred to as 2n
Examples: skin cells, blood cells, muscle cells.
Cells that have one copy of chromosomes are haploid.
The sperm and the egg are haploid.
They are called gametes.
egg
Sperm
Cell Division in Eukaryotes
There are two types of cell division in eukaryotes and both are examples of Asexual Reproduction.
Asexual reproduction is the production of offspring from one parent.
Mitosis
Occurs in organisms for:
Growth
Repair
Development
Asexual reproduction.
Meiosis
Forms gametes-sex cells (i.e. sperm and egg)
The Cell Cycle
Sequence of growth and division
Consists of two major phases:
Interphase and either Mitosis or Meiosis
Cells spend most of their time in Interphase (about 95% of the time)
Interphase consists of 3 phases:
G1 (Gap 1)-cell growth
S – DNA is synthesized
G2 (Gap 2)-cell prepares for division
Cells can also enter a G0 phase where they exit the cell cycle and do not copy their DNA or prepare for cell division. Most cells in the human body are in G0
Cell Cycle
The Cell Cycle
Interphase- the time between cell divisions
DNA is copied and centrioles duplicate in preparation for mitosis
time of rapid growth and metabolic activity
Remember-interphase is NOT part of mitosis. It is part of the cell cycle.
In interphase the nucleolus is still visible.
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Mitosis: The Phases
Prophase: the first and longest phase
nucleus and nucleolus disappear, centrioles migrate to opposite ends of cell
spindle fibers form-microtubules that radiate from the centrosomes.
DNA coils into rod-shaped chromosomes
prophase looks “grainy”
prophase
metaphase
An easy way to remember the phases P-MAT
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Mitosis: The Phases
Metaphase: The shortest phase
spindle fibers attach to centromeres
chromosomes line up on the equator and are held in place by the kinetochore fibers.
Mitosis: The Phases
Anaphase:
centromeres split and chromosomes move apart
each chromatid is now a separate chromosome
Mitosis: The Phases
Telophase: The last phase
After the chromosomes reach opposite poles, the spindle fibers disassemble.
cytokinesis occurs -(cytoplasm pinches cell in half)
chromosomes unwind, spindle breaks down, nucleus and nucleolus reform.
In plants- a cell plate forms in the middle of the dividing cell.
In animals-the cell membrane pinches off and eventually separates.
The Cell Cycle and Check Points
DNA synthesis (G2) Checkpoint-DNA repair enzymes check the result of DNA replication. If the DNA passes the check mitosis will begin.
Mitosis Checkpoint- Spindle fiber checkpoint. If the cell passes this checkpoint it will exit mitosis and begin G1 again.
Cell Growth Checkpoint-
proteins control whether the cell will continue to divide. If the cell is healthy proteins will initiate the S phase
Control of the Cell Cycle and Cancer
What we know:
Enzymes monitor the cell’s progress from phase to phase
If enzymes are produced at the wrong time or if there is over-production then they will cause uncontrolled dividing of cells= Cancer
Contact inhibition (when the cells touch) will cause cells to stop growing unless the cells are cancerous
Environmental factors can cause cancer.
Cancer: what we know…
Currently it is believed that cancer is caused by changes (mutations) in the genes that control cell cycle enzymes
Cancer causes tumors which deprive normal cells of the nutrients they need. (not all tumors are cancerous)
Eventually cancer cells invade the circulatory system and destroy major organs (metastasize)
Meiosis-Gamete Formation
As we go through the process of meiosis, compare it to what you learn about mitosis.
Meiosis is the process of nuclear division that reduces the chromosome number by half.
It begins with a germ cell (2n)- In organisms the reproduce sexually a germ cell is any biological cell that gives rise to the gametes(n)
Prophase I -continued
The chromosomes line up next to their homologous chromosomes. This pairing is called synapsis
Each pair of homologous chromosomes line up to form four sister chromatids called a tetrad.
Portions on the chromosomes break off and attach to the other chromatids. This is called crossing-over.
This creates genetic recombination or a new mixture of genetic material and is one reason you look different from your brother or sister.
tetrad
Metaphase I
Chromosomes line up in the midline-same as mitosis.
The chromosomes that line up are random and in the form of a tetrad
The spindle fiber from one pole attaches to the centromere of one homologous chromosome and the spindle fiber from the other pole attaches to the centromere of the other homologous chromosome.
kinetochore -a complex of proteins to which the microtubules of the spindle attach.
Anaphase I
Each homologous chromosome (consisting of two sister chromatids) moves to opposite poles.
The random assortment of the homologous chromosomes is called independent assortment.
Independent Assortment results in
genetic variation.
Telophase I and Cytokinesis
When the chromosomes reach the opposite ends of the cell cytokinesis occurs.
Each new cell contains a haploid number of chromosomes however each cell contains one chromosome from each of the homologous pair.
Each new cell has two copies of the original DNA (as chromatids) because it was copied during interphase.
Meiosis II-The second division
After meiosis I the cell enters meiosis II without entering interphase.
Prophase II- Chromosomes form and begin to move to the midline.
Metaphase II- The chromosomes are at the midline with each chromatid facing toward the opposite pole.
Anaphase II- the sister chromatids separate and move toward opposite poles.
Telophase II and Cytokinesis- The nuclear membrane forms around each new cell resulting in FOUR new cells.
Each new cell has half of the cell’s original number of chromosomes. (2n🡪n)
Meiosis I
Meiosis II
Spermatogenesis
The production of the sperm cell is called spermatogenesis.
Oogenesesis
The production of mature egg cells or ova is called Oogenesis.
(OH-ah-gen-uh-sis)
During cytokinesis I and II the cytoplasm divides unequally and as a result only one egg cell is produced while the other 3 are called polar bodies and breakdown.
Sexual Reproduction
Sexual reproduction is the production of offspring through the fusion of the sperm and egg gamete cells. They fuse to produce the zygote of a fertilized egg.
Offspring from sexual reproduction are genetically different from their parents as a result of the genetic recombination and independent assortment of the genes during meiosis.
Genetic variation is required for species to evolve and adapt to the ever-changing environment.
sperm
Egg