Chapter 8 Cell Growth and Division

1
Chapter 8Cell Growth and Division

• Charles Page High School
• Stephen L. Cotton

2
Section 8.1 - Cell Growth

• OBJECTIVES
• Describe cell growth.

3
Section 8.1 - Cell Growth

• OBJECTIVES
• Define cell division.

4
Section 8.1 - Cell Growth

• OBJECTIVES
• Relate cell growth to cell division.

5
Section 8.1 - Cell Growth

• Remember that living things
• are made up of cells
• grow, or increase in size
• In most cases, a living thing grows because it
  produces more cells
• An adult simply has more cells than an infant,
  not larger cells!

6
Section 8.1 - Cell Growth

• Why more cells, and not larger cells?
• Remember that materials enter and leave the cell
  membrane
• How quickly this exchange occurs depends upon the
  surface area of the cell
• But, how quickly food is used and wastes are made
  depends on the cell volume

7
Section 8.1 - Cell Growth

• The cells volume grows faster than the surface
  area
• If the diameter increases 10 times, the surface
  area increases 100 times, and the volume
  increases 1,000 times!
• Figure 8-2, page 160

8
Section 8.1 - Cell Growth

• 1. The fact that the surface area and volume do
  not increase at the same rate creates problems
  for the cell
• The larger cell will have a difficult time
  getting enough oxygen and nutrients in, and waste
  products out.
• This is a reason why cells do not grow much
  larger, even though the organism can

9
Section 8.1 - Cell Growth

• 2. Another reason cells stay small is that the
  cell does not make enough DNA directions to make
  more protein
• much like a town that has grown, but has not
  added a single book to their library- this
  results in an information crisis
• CELL DIVISION solves the problem!

10
Section 8.1 - Cell Growth

• Cell division- the process whereby the cell
  divides into two daughter cells
• Most cells are about the same size, whether they
  come from an elephant or a mouse
• Rates of cell growth? Some very fast- a E. coli
  can easily double its volume in about 30
  minutes then it divides.

11
Section 8.1 - Cell Growth

• If they can divide this fast, why have they not
  taken over the world?
• They quickly use up the available nutrient
  supply, and the rate of growth slows.
• There are controls on cell growth
• certain places (heart, nerves) rarely ever divide
• skin and digestive system divide often

12
Section 8.1 - Cell Growth

• Some cells receive more wear and tear, thus
  they may need to be replaced often
• The controls on growth can be turned on and
  off
• an injury such as a cut or broken bone causes
  cells at the injury site to be stimulated to
  divide rapidly
• this slows as healing nears completion

13
Section 8.1 - Cell Growth

• Uncontrolled cell growth can be severe
• Cancer- cells have lost their ability to control
  their rate of growth they continue to grow (for
  no apparent reason) until their supply of
  nutrients is exhausted

14
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• OBJECTIVES
• Define mitosis and cytokinesis.

15
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• OBJECTIVES
• Describe the cell cycle, and the changes that
  take place during interphase.

16
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• OBJECTIVES
• Discuss the events and the significance of
  mitosis.

17
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• The division of eukaryotic cells occurs in two
  main stages
• 1. Mitosis- the process by which the nucleus
  divides into two nuclei, each with the same
  number and kinds of chromosomes as the parent
  cell

18
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• The division of eukaryotic cells occurs in two
  main stages
• 2. Cytokinesis- the process by which the
  cytoplasm divides, thus forming two distinct
  cells.
• Because eukaryotic cells are complex, the process
  of cell division is also complex thus it is a
  delicate process.

19
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• CHROMOSOMES- are structures in the cell that
  contain the genetic information that is passed
  from one generation to the next
• prokaryotic cells have chromosomes made up of
  long circular molecules of DNA
• eukaryotic- made of distinct lengths

20
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• Each organism has a distinct number of
  chromosomes (Fig. 8-7, page 165)
• humans have 46 goldfish have 94, etc.
• Chromosomes are made of chromatin, which is made
  of DNA and protein
• During early division, the chromatin condenses
  and the chromosomes become more visible.

21
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• Much of the protein is involved in folding the
  DNA to fit into the nucleus and it is in the
  shape of a double helix
• 1973, it was discovered that the chromosomes DNA
  was coiled around special proteins called
  histones
• DNA histones beadlike structures called
  nucleosomes- form a thick fiber

22
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• Chromosome structure
• When the chromosomes are more visible, it is the
  start of mitosis
• At this point, they contain two chromatids,
  attached to each other by a centromere (Fig.
  8-9, page 166)

23
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• THE CELL CYCLE
• this is the period from the beginning of one
  mitosis to the beginning of the next
• during this time, the cell grows, prepares for
  division, and divides into the two new daughter
  cells
• it includes mitosis (the period of active
  division), interphase (a period of no division),
  as well as cytokinesis

24
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• THE CELL CYCLE (continued)
• Mitosis is represented as the M phase, and this
  is when the nucleus divides
• Interphase is divided into 3 phases
• 1. G1 (gap 1)
• 2. S (DNA synthesis)
• 3. G2 (gap 2)
• G1 and G2 -periods of growth/activity

25
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• THE CELL CYCLE (continued)
• The time required to complete a cycle is the time
  required for it to reproduce itself, and not all
  cells move through the cycle at the same rate
• human muscle and nerve cells do not divide at all
  once they have developed
• digestive linings grow/divide rapidly

26
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• INTERPHASE- this is the period between divisions,
  and can be quite long. The actual division takes
  place quickly.
• G1 - (gap 1) - period of activity in which cell
  growth and development takes place
• this is followed by the S phase

27
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• INTERPHASE (continued)
• S phase - DNA synthesis. This is when the DNA is
  replicated, and several other proteins are
  synthesized.
• This is the longest part of Interphase
• G2 - (gap 2) - usually shortest time, involves
  the synthesis of organelles and materials for
  cell division

28
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• During interphase, the nucleus is active in
  synthesizing messenger RNA in order to direct
  cellular activities.
• Although it seems to be a quiet phase (mainly
  growth), it is actually a period of intense
  activity.
• Fig. 8-11, page 167

29
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• Mitosis (or the M phase) is the process of
  dividing the nucleus into two nuclei
• may last anywhere from a few minutes to several
  days
• Divided into 4 phases 1)
  prophase, 2) metaphase, 3) anaphase,
  and 4) telophase

30
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 1. PROPHASE
• this is the longest phase of mitosis, often
  taking 50-60 of the time
• first clue for prophase is that the chromosomes
  are beginning to appear distinctly (chromatids
  attached by a centromere)

31
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 1. PROPHASE (continued)
• centrioles separate, and position themselves at
  opposite sides of the cell (plants do not have
  centrioles)
• the condensed chromosomes attach to the spindle
  (a mesh- like structure that helps move the
  chromosomes apart)

32
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 1. PROPHASE (continued)
• the centrioles and spindle are composed of the
  type of protein called microtubules
• near the end of prophase, the nucleolus
  disappears, and the nuclear envelope breaks down
• Fig. 8-12, page 168

33
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 2. METAPHASE
• as prophase ends, metaphase will automatically
  begin
• this is the shortest time period, only lasting a
  few minutes
• the chromosomes line up at the equator across the
  center of the cell
• they connect to the spindle

34
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 2. METAPHASE (continued)
• the ends of the spindle are star-like structures
  called asters, which act like small anchors
• Fig. 8-14, page 169

35
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 3. ANAPHASE
• this is the third phase of mitosis
• the centromeres that join the chromatids split
• the chromosomes repel each other to opposite
  sides of the cell
• Fig. 8-15, page 169

36
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 4. TELOPHASE
• the final phase of mitosis
• the chromosomes (which have been very distinct)
  now begin to coil together into a mass
• nuclear envelope reforms
• spindle breaks down

37
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• 4. TELOPHASE (continued)
• the nucleolus becomes visible in each daughter
  cell nucleus
• Fig. 8-16, page 170
• Mitosis is now complete however, the process of
  cell division is not

38
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• CYTOKINESIS
• At this point, two nuclei (each with a duplicate
  set of chromosomes) are formed.
• Now, we need to divide the cytoplasm (materials
  outside the nucleus)
• cytokinesis- the division of the cytoplasm into
  two cells

39
Section 8.2 - Cell Division Mitosis and
Cytokinesis

• CYTOKINESIS (continued)
• In animals, the cell membrane moves inward and
  pinches off
• In plants, a structure called the cell plate
  forms midway between the divided nuclei then a
  cell wall begins to appear in the cell plate
• Fig. 8-17, page 170
• The cell now re-enters Interphase, and continues
  to grow and function.