Chapter%208%20and%2010b

1
Chapter 8 and 10b

• Cell Processes
• Cells do What?

2
Osmosis

• What is diffusion? (review)
• Osmosis is the diffusion of water across a
  selectively permeable membrane
• This maintains homeostasis in the cell

3
Cells in an Isotonic Solution

• Isotonic solution - the concentration of
  dissolved substances in the solution is the same
  as the concentration of dissolved substances
  inside the cell
• Water does go in and out of the cell, but there
  is no net change in concentration

animation
4
Cells in a Hypotonic Environment

• Hypotonic solution - the concentration of
  dissolved substances is lower in the solution
  outside the cell than the concentration inside
  the cell
• Therefore, water moves through the plasma
  membrane into the cell
• Pressure increases inside against the cell
  membrane and
• Animal cells may burst
• Plant cells become more firm as they expand
  against the cell wall. (grocery stores)

5
Hypotonic
6
Cells in a Hypertonic Solution

• Hypertonic solution - the concentration of
  dissolved substances outside the cell is higher
  than the concentration inside the cell
• Water moves out of the cell
• In animals, cells shrivel
• In plants, membrane shrink away from cell wall

7
Osmosis Lab
8
Passive Transport

• The movement of molecules across a membrane by
  diffusion (no energy required)
• Facilitated Diffusion is passive transport across
  the cell membrane using proteins
• Transport proteins form a channel to allow
  specific molecules to flow across
• Carrier proteins change shape to allow a
  substance to pass through the plasma membrane

Animation
9
Facilitated Diffusion
10
Active Transport

• The movement of materials through a membrane
  against a concentration gradient
• Requires energy
• Carrier proteins have a specific shape to allow
  them to bind with specific molecules
• Then then change shape (with energy) so molecule
  can be transported across
• Carrier protein resumes original shape

11
Active Transport
12
Transport of Large Molecules

• Endocytosis - process by which a cell surrounds
  and takes in material from its environment
• Membrane forms around material and engulfs it
• Exocytosis - the expulsion of materials from a
  cell (wastes, hormones)
• Membrane surrounds material and takes it to
  membrane, opens up.

13
Endocytosis
Exocytosis
14
Section 1 Review

• What factors affect osmosis?
• How do animal and plant cells react differently
  in a hypotonic solution?
• How are facilitated diffusion and active
  transport similar? How different?
• How do carrier molecules facilitate transport of
  molecules across a membrane?
• A paramecium expels water when in freshwater.
  What kind of internal environment does it have?

15
Cell Size Limitations

• Most cells are between 2 and 200 ?m in diamater
• Red blood cells - 8 ?m
• Yolk of ostrich egg - 8 cm
• Why cant we have big cells?
• Diffusion works slowly over large distances
• DNA can only work so fast
• Surface to volume ratio
• As size increases, the volume increases faster
  than the surface area
• Cell membrane would back up with all the
  nutrients coming into and out of a large cell

16
Surface to Volume Ratio
1 mm
2 mm
1 mm
1 mm
2 mm
2 mm
4 mm
4 mm
4 mm
What is the surface area of each? What is the
volume of each?
17
(No Transcript)
18
Cell Division Chromosomes

• Cell Division is the process by which new cells
  are produced from one cell
• Two new cells identical to original
• Early biologists discovered that chromosomes
  appear during cell division and then disappear
• Later, found importance of chromosomes (DNA)
• When not dividing, chromosomes exist as chromatin
  - long strands of DNA wrapped around proteins
  called histones (groups of histones are called
  nucleosomes)
• Upon division, they condense and organize into
  chromosomes

19
Chromosomes
The centromere plays an important role in the
movement of chromosomes during mitosis
back
20
The Cell Cycle

• The cell cycle is the sequence of growth and
  division of a cell
• The majority of a cells life is spent in a
  period of growth and normal function called
  interphase
• Following interphase, a cell enters its period of
  division, called mitosis
• Mitosis is the process by which two daughter
  cells are formed, each containing a complete set
  of chromosomes
• Following mitosis, is cytokinesis, where the
  cytoplasm divides, separating the two daughter
  cells

21
The Cell Cycle
22
Phases of Mitosis - Prophase

• Prophase - 1st and longest phase
• Chromatin condenses into chromosomes
• Each duplicated chromosome has two halves, called
  sister chromatids
• The nucleus begins to disappear
• The nucleolus and nuclear envelope disintegrate
• Centrioles migrate to opposite corners
• Centrioles are small, dark, cylindrical
  structures made of microtubules that play a role
  in chromatid separation

23
Were still on Prophase

• The spindle starts to form between the centrioles
• The spindle is a football-shaped, cagelike
  structure consisting of thin fibers made of
  microtubules that helps separate sister
  chromatids later on

Interphase
Prophase
24
The Phases of Mitosis - Metaphase

• Shortest phase
• The doubled chromosomes (sister chromatids)
  become attached to the spindle fibers by their
  centromeres
• Chromosomes are pulled and line up at the midline
  or equator of the cell
• Each sister chromatid is
  attached to a spindle fiber
  at one pole

25
The Phases of Mitosis - Anaphase

• The spindles pull the sister chromatids apart
• This marks the beginning of anaphase
• The centromeres split
• The chromatids are
  pulled apart by the
  shortening of the
  microtubules in the
  spindle fibers

26
The Phases of Mitosis -Telophase

• Begins as the chromatids reach the opposite poles
  of cell
• Chromosomes begin to unwind
• Spindle breaks down
• Nucleolus reappears and
  nuclear envelope forms
  around chromosomes
• A new double membrane begins
  to form between two
  new nuclei

27
Cytokinesis

• Differs in plants and animals
• In animals, the plasma membrane pinches in along
  the equator

28
Cytokinesis

• In plants, a cell plate is laid down across the
  cell equator
• Then, a cell membrane forms around each new cell
  and new cell walls form on each side of the cell
  plate

29
(No Transcript)
30
Results of Mitosis

• In unicellular organisms, the organism simply
  multiplied
• In multicellular organisms, two new cells are
  created to replenish dead cells or contribute to
  the growth of the organism
• Guarantees genetic continuity (new cells do
  things the same way as the old cells)

Cell Cycle Quiz
31
Levels of Organization

• Cell
• Ex muscle cell
• Tissue - groups of cells that work together to
  perform a specific function
• Ex muscle tissue
• Organs - tissues organized in various
  combinations that perform complex roles
• Ex stomach
• Organ System - multiple organs that work together
• Ex digestive system
• Organism all the organ systems working together
• Ex Florida panther

32
Section 2 Review

• Describe how a cells surface-to-volume ratio
  limits its size.
• Why is it necessary for a cells chromosomes to
  be distributed to its daughter cells in such a
  precise matter?
• Describe what happens in prophase. In metaphase.
  In telophase. In anaphase.
• Describe the phases of the cell cycle.
• Give an example at each level of organization in
  an organism.

33
Normal Control of the Cell Cycle

• Proteins called cyclins and a set of enzymes that
  attach to the cyclin control the cell cycle
• Research points to the portion of interphase just
  before DNA replication as a key period in the
  cell cycle
• Enzyme production is directed by genes located on
  chromosomes
• A gene is a segment of DNA that controls the
  production of a protein
• These control how fast or how slow the cell cycle
  needs to proceed.
• When would the cell cycle need to speed up or
  slow down?

34
Cancer

• Cancer is a malignant growth resulting from
  uncontrolled cell division
• This failure to control cell growth may result
  from not producing enzymes, overproducing
  enzymes, or producing the wrong enzymes at the
  wrong times.
• Currently, scientists think
  cancer starts because of
  changes in one or more
  of the genes that produce
  substances to control the
  cell cycle

35
Cancer

• Tumors grow and deprive normal cells of nutrients
• In later stages, the cancer spreads throughout
  the body (called metastasis)
• Leading cause of death in the United States
  (heart disease now 2)
• Can be genetically caused
• Can be environmentally caused
• Cigarette smoke, air and water pollution,
  exposure to UV rays from the sun, viral infections

Animation
36
Cancer Prevention

• Diets low in fat and high in fiber can reduce the
  risk of cancer
• Ex fruits, vegetables and grain products for
  fiber
• Vitamins and minerals may also help prevent
  cancer
• Expecially carotenoids (found in yellow, orange,
  and green leafy vegetables), vitamins A, C, and
  E, and calcium
• Exercise, not smoking and other healthy habits
  are known to reduce the risk also

37
Section 3 Review

• Do all cells complete the cell cycle in the same
  amount of time?
• What controls the cell cycle?
• How can disruption of the cell cycle result in
  cancer?
• How does cancer affect normal cell functioning?
• What can be done to help reduce the risk of
  cancer?

38
Diploid Cells

• In animals and most plants, chromosomes occur in
  pairs one from each parent
• A cell with two of each kind of chromosome is
  called a diploid cell and contains a diploid, or
  2n, number of chromosomes

39
Haploid Cells

• Organisms produce gametes that contain one of
  each kind of chromosome
• Called haploid, and has a haploid, or n, number
  of chromosomes

40
Homologous Chromosomes

• The two chromosomes of each pair in a diploid
  cell are called homologous chromosomes
• The chromosomes contain the same genes in the
  same order, but might not be identical (unless
  parents genotypes are identical)

41
Why Meiosis?

• Why wont mitosis work for making gametes?
• Cell division which produces gametes containing
  half the number of chromosomes as a parents body
  cell is called meiosis
• Why is this good?
• Meiosis consists of two separate divisions
• Meiosis I
• Meiosis II

42
Why Meiosis?

• By the end of meiosis II, there are four haploid
  cells called sex cells or gametes
• Male gametes are called sperm or pollen
• Female gametes are called eggs
• Fertilization is when sperm and egg unite
  produces a zygote (fertilized cell)
• Fusion of haploid sex cells is called sexual
  reproduction
• Example Male is 2n46, gamete is n23
• Female is 2n46, gamete n23
• After fertilization, new zygote is 2n46
• Mitosis then takes over and organism grows

43
Phases of Meiosis

• Other than what happens to the chromosomes,
  everything else in meiosis is essentially the
  same as in mitosis
• Interphase
• Cell replicates its chromosomes
• End up with two identical sister chromatids, held
  together by a centromere

44
Prophase I

• Chromosomes coil, spindle forms, etc.
• Homologous chromosomes line up with other to form
  a four-part structure called a tetrad
• A tetrad is two homologous chromosomes (one from
  mom, one from dad), each made of two sister
  chromatids
• The chromatids are paired so tightly that
  chromosomes can actually break and exchange
  genetic material
• Process called crossing over
• This can occur at any part of a chromatid and can
  occur several times
• Crossing over results in the new combinations of
  alleles resulting in different people
• Each pair of homologous chromosomes averages 2-3
  crossovers in humans

45
Metaphase I

• Centromeres become attached to spindle fiber
• Tetrads pulled to equator of cell

46
Anaphase I

• Homologous chromosomes, each with its two
  chromatids, separate and move to opposite ends of
  the cell
• Centromeres dont split
• Ensures that each new cell will only receive one
  chromosome from each homologous pair
• Errors happen here often

back
47
Telophase I

• Spindle broken down
• Chromosomes uncoil
• Cytoplasm divides
• Each cell has half the genetic information of the
  original cell
• This is because it has only one chromosome from
  each homologous pair
• This chromosome is still doubled

48
(No Transcript)
49
Meiosis II

• Some cells rest between stages
• Other cells go from Anaphase I straight to
  metaphase of meiosis II
• PMAT proceed much like mitosis
• End up with one copy of each chromosome (haploid)

50
Meiosis Animation
Mitosis vs. Meiosis
51
Section 2 Review

• How are the cells at the end of meiosis different
  from the cells at the beginning of meiosis?
• What does haploid mean? Diploid?
• If the diploid number of a plant is 10, how many
  chromosomes would you expect to find in its
  triploid offspring?