DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms.
Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.
TEXT: Chapter 8, section 1: page 151-153
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.
Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.
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CHROMOSOME DURING MITOSIS METAPHASE (2 chromatids, duplicated DNA)
The chromosome seen here is already duplicated. It has two chromatids (the left and right), and a centromere( where the two chromatids are joined.
A chromosome can consist of either a single copy of DNA , or a duplicated copy of DNA. Both are considered to be chromosomes.
If we unwind a chromosome, we will see that a chromosome is made of chromatin (threads of double-stranded DNA) that is tightly wound up around circular proteins called histone.
Define:
1.
Chromosome
2.
Chromatid
3.
Centromere
4.
Chromatin
5.
Histone
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The picture shown below is called a karyotype. This is the karyotype of a human. A karyotype is a picture of all the chromosomes that are in a single human cell. The X and Y chromosomes determine the gender of the person and are called sex chromosomes (XX is female and XY is male). All other chromosomes (pairs 1-22) are called autosomes.
Autosomes come in different shapes and sizes but each autosome has another chromosome (its homologue) that contains the same genes. Autosomes contain genes that are not associated with gender, such as eye color, height, hair color , etc.
A diploid cell contains a pair of each autosome and a pair of sex chromosomes. A haploid cell contains only one of each autosome and one sex chromosome. Haploid cells are eggs and sperm and must combine with another haploid cell during fertilization to produce offspring (sexual reproduction)
1.
What is an Autosome?
2.
What is a Sex Chromosome
X
Y
3.
What is a Homologous pair?
4.
Haploid (which karyotype on the next page is haploid? What does it mean to be haploid?) a.
Diploid (which karyotypes are diploid? _______ which is diploid AND duplicated? _____
5.
Can you have a karyotype that is haploid? What type of cell has only “half the chromosomes “
(haploid). What type of cells in your body are diploid?
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Here are images of homologous pairs of chromosomes that have not duplicated their DNA (left) and homologous pairs that have duplicated their DNA (right). Both of these sets are diploid (2 homologous chromosomes). However , the set on the right has duplicated DNA as well (it is in metaphase).
Karyotype A Karyotype B
Karyotype C
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- Read the chapter in your book on Mitosis (pg154 – 159) and answer the following questions
1.
All cells come from pre-existing cells. What is the division of prokaryotic cells called? How many chromosomes does a bacteria have and what is it’s shape?
2.
What is the cell cycle and in what type of cells does the cell cycle occur? ?
3.
What two processes need to happen for one cell to divide into 2 completely separate cells?
4.
Draw a picture of a chromosome and label the centromere and chromatid.
5.
How many total chromosomes does a human cell have? a.
How many are autosomes? b.
How many are sex chromosomes? c.
What sex chromosomes do Males have? d.
What sex chromosomes do Females have?
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6.
Define the terms Haploid and Diploid. Then provide examples of each type of cell.
7.
What is mitosis?
8.
List the 4 phases of mitosis and briefly describe what happens in each phase.
9.
How is cancer related to the cell cycle?
10.
What kind of molecules control the cell cycle?
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html
Be sure to watch the animation above. It will help you to visualize how the cell cycle works.
The cell cycle, or cell-division cycle is:

A series of events that takes place in a eukaryotic (with a nucleus) cell leading to its division and replication.

The cell cycle can be divided into two MAJOR periods: o Interphase
— during which the cell grows, accumulating nutrients needed for mitosis and duplicating its DNA

G1, S, G2 o M phase , during which the cell splits itself into two distinct cells, often called
"daughter cells. This involves both

Mitosis replication of the chromosomes formation of two nuclei AND

Cytokinesis involves actually splitting the single cell into two distinct daughter cells.
The cell-division cycle is a vital process by which a single-cell fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed.
1.
Describe the phases of the cell cycle
2.
Describe the phases of mitosis
3.
Define cytokinesis
After cell division, each of the daughter cells begin the interphase of a new cycle. Although the various stages of interphase are not usually morphologically distinguishable, each phase of the cell cycle has a distinct set of specialized biochemical processes that prepare the cell for initiation of cell division.
The Cell Cycle :
The cell cycle consists of four distinct phases:
G1 phase, S phase (synthesis), G2 phase (collectively known as interphase)
M phase (mitosis and cytokinesis).
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Activation of each phase is dependent on the proper progression and completion of the previous one.
Cells that have temporarily or reversibly stopped dividing are said to have entered a state of quiescence called G0 phase.
G1 phase.
Metabolic changes prepare the cell for division (cellular contents are duplicated). At a certain point - the restriction point - the cell is committed to division and moves into the S phase.
S phase.
DNA synthesis replicates the genetic material. Each chromosome now consists of two sister chromatids.
G2 phase.
Metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis. DNA is
“proofread” for accuracy
M phase.
A nuclear division (mitosis) followed by a cell division (cytokinesis or division of the cytoplasm).
The period between mitotic divisions - that is, G1, S and G2 - is known as interphase.
G0
Many times a cell will leave the cell cycle, temporarily or permanently. It exits the cycle at G1 and enters a stage designated G0 (G zero). A G0 cell is often called "quiescent". Many G0 cells are anything but quiescent. They are busy carrying out their functions in the organism. e.g., secretion, attacking pathogens.
Often G0 cells are terminally differentiated: they will never reenter the cell cycle but instead will carry out their function in the organism until they die. For other cells, G0 can be followed by reentry into the cell cycle. Most of the lymphocytes in human blood are in G0. However, with proper stimulation, such
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as encountering the appropriate antigen, they can be stimulated to reenter the cell cycle (at G1) and proceed on to new rounds of alternating S phases and mitosis.
G0 represents not simply the absence of signals for mitosis but an active repression of the genes needed for mitosis. Cancer cells cannot enter G0 and are destined to repeat the cell cycle indefinitely.
Mitosis:
During mitosis replicated chromosomes become positioned near the middle of the cytoplasm and then segregated so that each daughter cell receives one of the chromatids from each chromosome (one copy of the original DNA (if you start with 46 in the parent cell, you should end up with 46 chromosomes in each daughter cell).
Prophase
Prophase is the first stage of mitosis proper. Chromatin condenses (the chromatin/DNA replicate during
Interphase, so it is now “coiling into chromosomes), the nuclear envelope dissolves, centrioles (if present) divide and migrate and the spindle forms.
Metaphase
Metaphase follows Prophase. The chromosomes (which at this point consist of 2 identical chromatids held together by a centromere) migrate to the equator of the spindle, where the spindles attach to the kinetochore fibers.
Anaphase
Anaphase begins with the separation of the centromeres, and the pulling of chromosomes (we call them chromosomes after the centromeres are separated) to opposite poles of the spindle. To do this cells utilize microtubules (referred to as the spindle apparatus) to "pull" chromosomes into each "cell".
Animal cells (except for a group of worms known as nematodes) have a centriole. Cells that contain
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centrioles also have a series of smaller microtubules, the aster, that extend from the centrioles to the cell membrane. The aster is thought to serve as a brace for the functioning of the spindle fibers.
Telophase
Telophase is when the chromosomes reach the poles of their respective spindles, the nuclear envelope reforms, chromosomes uncoil into chromatin form, and the nucleolus (which had disappeared during
Prophase) reform. Where there was one cell there are now two smaller cells each with exactly the same genetic information. These cells may then develop into different adult forms via the processes of development.
Cytokinesis
Cytokinesis is the process of splitting the daughter cells apart. Whereas mitosis is the division of the nucleus, cytokinesis is the splitting of the cytoplasm and allocation of the organelles and cytoplasm into each new cell.
1.
Diagram the cell cycle. Identify all phases of interphase and the M phase, and briefly identify what takes place in each phase.
2.
What is the G0 phase? What types of cells might go through a G0 phase? Why?
3.
Which cells never go through a G0 phase? What is the result?
4.
What is the key event in mitosis? How does the cell ensure that each daughter cell gets exact copies of the DNA (all chromosomes).
5.
How would you differentiate mitosis and cytokinesis?
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