Download Chromosomes

The Cell Cycle and Chromosomes
http://www.cellsalive.com/cell_cycle.htm
A. Cells spend most of
their lives in
interphase—growing
(G1) and preparing for
division.
The Cell Cycle and Chromosomes
http://www.cellsalive.com/cell_cycle.htm
1. Cells that do not “plan” on
dividing go into a stalled state
called G0 (gap 0)-examplebrain neurons & muscle cells
Some cells will stay in G0
until they need to divideexample-white blood cells
B. Cell Division is an important function performed by
cells after their “growth or G1” phase
For example, skin cells need
to divide frequently to
provide a protective layer
for our body.
C. Draw and label the cell
cycle (be sure to include
interphase and cell division):
II. DNA and Chromosomes-After Gap 1
and DNA replication (interphase), DNA
forms chromosomes
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II. DNA and Chromosomes
A. In prokaryotic cells, DNA is located in the cytoplasm.
1. Most prokaryotes have a single DNA
molecule/chromosome containing most of the cell’s
genetic information.
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2. Prokaryotes have “extra” circular pieces of DNA
called “plasmids”. Fill in the term plasmid in your
bacterial cell diagram on your notes.
tic cells also have “extra” circular pieces of
DNA called “plasmids” that function and
replicate independent of the cell’s main
DNA or may become a part of the main
DNA. Label the “plasmid DNA” on the
prokaryote diagram:
II. DNA and Chromosomes
B. Many eukaryotes have 1000 times the
amount of DNA as prokaryotes.
1. Eukaryotic DNA is stored as
chromatin in the nucleus. DNA
chromatin forms chromosomes
during cell division.
2. The number of chromosomes varies
widely from one species to
another.
3. Most species have matching
“homologous” pairs of
chromosomes-one from each
parent (humans have 23 pairs for a
total of 46).
a. Species with 2 genders
(humans) have 2 sex
chromosomes that don’t match
(X,Y).
C. Chromosome Structure
1. Eukaryotic chromosomes contain DNA and protein, tightly packed
together to form chromatin.
a. Chromatin consists of DNA tightly coiled around proteins called
histones.
b. DNA and histone molecules form nucleosomes.
c. Nucleosomes pack together, forming a thick fiber.
d. Each cell contains about 2 meters worth of DNA, a single person
as enough DNA to stretch from the Earth to the Sun more than
400 times. (150 billion meters)
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Chromatin vs. Chromosome
Chromatin
Chromosomes
Unwound DNA
Found throughout
interphase of cell cycle
DNA is being used for
protein synthesis (strands
are more accessible)
Tightly
packaged/condensed DNA
Formed only during cell
division after replication
DNA is not being used for
protein synthesis
Copyright Pearson Prentice Hall
Cell Cycle and Chromosomes
Name that species!
Instructions: Groups of two students will be assigned a random species. You will need to
find the answers from ch. 5.2 (p. 138-139) and ch. 6.1 (p. 168) and from the species
information provided on your handout.
1.
What are chromosomes and how many does your species have (notes and p.
138)?
2.
Explain Fig. 5-5 in terms of size---when is DNA most visible? Arrange the DNA
descriptions from least visible to most visible (there are 5 headings/descriptions to
arrange).
3.
Is your species a eukaryotic organism or prokaryote? If it is a prokaryote, how is the
DNA/chromosome different from eukaryotes? (p. 556)
4.
Draw and label an example chromosome of your species (see figure 5.5)
5.
6.1 (p. 168) What are sex chromosomes and How many sex chromosomes do most
organisms have?
6.
What are autosomes and how many does your organism have?
7.
What are homologous chromosomes and how many does your organism have?
8.
What is the difference between diploid and haploid cells? Which cells of most
organisms are diploid? Which are haploid? Why?
9.
Be ready to present your findings.