2. Main goals for this
lecture
1. Distinguish between
chromosomes, chromatids, and
chromatin
2. Correctly model and identify in
pictures each stage of the cell
cycle
3. The Main Ideas
1. Cell division results in 2 genetically
identical daughter cells
2. The mitotic phase alternates with
interphase in the cell cycle
4. The unity of life
• All living things reproduce
• Reproduction occurs at the cellular level
5. The many functions of
cell division
• REPRODUCTION: In unicellular organisms leads to an increase in the size of the population
• In multicellular organisms – GROWTH: a single fertilized egg (zygote) divides to
form a new organism
– REPAIR: Repairs and renews old or damaged cells
6. Cell Division results in
identical daughter cells
• The DNA is copied
and divided between
the 2 new cells
• Each new cell
(daughter) contains
an exact copy of the
original DNA
• In human cells, there is about 6 feet of DNA to copy
and neatly and accurately divide between the 2 new
cells!
8. DNA
• A cell’s genetic information
is called its genome
– In bacteria (prokaryotic cells)
it is usually 1 long circular
DNA molecule
– In plants, animals, and fungi
(eukaryotic cells) is it usually
several linear molecules of
DNA
9. Chromosomes
• The individual molecules of DNA are
packaged into chromosomes
• Each species has a characteristic number of
chromosomes
–
–
–
–
–
–
Humans - 46
Camel 70
Alligator - 32
Chicken - 78
King crab - 208
Corn - 20
10. Quick Think
Is the complexity of the
organisms directly
proportional to the number
of chromosomes? Explain
your answer.
11. Chromosomes
• Chromosomes
are made of
chromatin
– DNA + proteins
• THE DNA PART:
Each
chromosome is a
single long piece
of DNA coding for
100s or 1000s of
genes
12. Chromosomes
• THE PROTEIN
PART: the
proteins help
keep the shape
of the
chromosome
and help control
the activity of
the genes
13. Quick Think
• So…what’s a chromosome?
•
•
•
•
What is it made of?
What is it’s purpose?
Where is it found?
How many do we have?
14. Chromosomes
• When the cell is dividing the DNA is tightly
packed into X-shaped chromosomes
• When the cell is not dividing, the DNA is more
loose - just chromatin strands
15. Quick Think
• How does the appearance of
chromatin and chromosomes
vary?
• Draw them…?
16. Getting the DNA ready
for cell division
• Before a cell divides, the DNA
(chromatin) condenses and •
folds into a neat, tightly
packed chromosome
Each chromosome is
made up of 2 sister
chromatids identical copies of
that particular
chromosome
17. Chromosomes
• The 2 sister
chromatids are
attached with sticky
proteins
• The place where they
are attached is called
the centromere
19. Chromosomes
• During cell division, the 2 sister
chromatids are pulled apart to opposite
ends of the cell and repackaged into
new nuclei
• They are now considered
individual chromosomes
20. Mitosis
• The formation of 2
daughter nuclei Notice
! Not
• Followed by the 2 new cells.
2 new
division of the nuclei
.
cytoplasm and
organelles called
cytokinesis
21. Mitosis and Interphase
• Mitotic (M) phase - ~10% of a cell’s life
• Interphase - ~90% of a cell’s life
22. Interphase
• During this time
the cell:
– grows
– produces proteins
& organelles
– copies its
chromosomes
– Prepares for cell
division
23. Interphas
e
• 3 phases:
– G1 phase = first gap
• Cell is making proteins and
organelles
– S phase = synthesis
• Cell is making proteins and
organelles
• DNA IS COPIED
– G2 phase = second gap
• Cell is making proteins and
organelles
25. What happens in each
phase
• At the end of interphase:
– DNA has been copied
– DNA not in chromosomes yet
– Nucleus intact
– The centrosome (an organelle
that helps organize the mitotic
spindle fibers) replicates
26. What happens in each
phase
• Prophase:
–
–
–
–
Chromosomes now tightly coiled
Sister chromatids joined together
Nucleoli disappear
Mitotic spindle begins to form
27. What happens in each
phase
• Prometaphase:
– Nuclear membrane breaks up
– Microtubles from spindle start to connect with
chromosomes
– Each sister chromatid has a kinetochore protein in
the centromere where the spindle fiber attaches
28. • What is the primary difference between
prophase and prometaphase?
29. What happens in each
phase
• Metaphase:
– The spindle fibers push
the sister chromatids until
they are all lined up at
the metaphase plate (the
middle of the cell)
30. What happens in each
phase
• Anaphase:
– The sister chromatids are pulled apart by
the spindle fibers
31. What happens in each
phase
• Telophase:
– New daughter nuclei begin to form around each set of
chromosomes
– Chromosomes start to unwind
34. What happens in each
phase
• Cytokinesis:
– Division of the
cytoplasm
– In animal cells, the
two new cells
“pinch” apart
– In plant cells, a new
cell wall forms
between the 2 new
daughter cells
