Cells

1
Cells

• Topic 2
• Chapters 4,5,9

2
2.1 Cell Theory

• Chapter 4

3
2.1.1

• Scientists first became aware of cells as the
  basic building blocks of life in the 1600s
• Made possible by the invention of the microscope
• Robert Hooke first coined the term cell after
  observing cork in 1655
• Anton Van Leeuwenhoek first observed living cells
  in pond water in 1674

4
2.1.2

• Modern scientists follow the cell theory, which
  was proposed by Rudolf Virchow in 1855
• The cell theory consists of three components
• All living organisms are composed of cells
• Cells are the smallest unit of life
• All cells come from pre-existing cells

5
2.1.2

• Supporting Evidence for the Cell Theory
• While cells may be composed of smaller parts
  called organelles, the cell itself is the
  smallest unit of life that can show all the
  characteristics of living processes (e.g
  metabolism and reproduction)
• The division of cells to create new cells has
  been observed with microscopes

6
2.1.2

• Supporting Evidence for the Cell Theory
• Experiments refuting Spontaneous Generation also
  provided evidence.

7
2.1.2

• Exceptions to the cell theory dont follow the
  usual cell model
• Muscle Cells
• Long fibers that have more than one nucleus
  (organelle where DNA is located) per cell

8
2.1.2

• Fungal Hyphae
• Fungal cells are long strands called hyphae that
  together form dense networks called mycelium
• The hyphae are multinucleated and have cell walls
  composed of chitin (normal cell walls are
  composed of cellulose)

9
2.1.2

• Unicellular organisms are considered possible
  exceptions because they are larger in size than
  the cells of multicellular organisms
• Some tissues/organs contain large amounts of
  non-cellular material
• The eye is filled with a liquid called the
  vitreous humour
• Bone is primarily composed of mineral deposits

10
2.1.3

• As mentioned previously, all cells, even those
  that are simple unicellular organisms (i.e.
  bacteria) carry out the basic functions of life.
  These basic functions are
• Metabolism breaking down glucose and other
  nutrients in order to make ATP (the most basic
  unit of cellular energy)
• Response to outside stimuli
• Homeostasis maintenance of a stable internal
  environment

11
2.1.3

• Growth in the case of cells this means an
  increase in size and volume
• Reproduction - cell division to create two cells
  from one
• Nutrition for cells this refers either to the
  synthesis of organic molecules (e.g. plants
  creating glucose) or the absorption of organic
  matter (fungi absorbing nutrients from decaying
  organisms)

12
2.1.4

• Relative sizes of microscopic objects
• Molecules 1 nm
• Cell Membrane thickness 10 nm
• Viruses 100 nm
• Bacteria 1 um
• Organelles up to 10 um
• Most cells up to 100 um
• It should be noted that the above measurements
  are taken in two dimensions yet cells and their
  components are three dimensional

13
2.1.4
14
2.1.5

• Calculating Magnification
• It is important to know how to calculate the
  actual size of an object based on its size in a
  drawing or a picture taken from a microscope
• The actual size of the object measured length
  (using a ruler)/magnification
• In the case of the image to the right
• Actual size 60mm/10 6 mm
• 6 mm X 1,000 um 6,000 um

Magnification is 10 X
Measured length is 60 mm
15
2.1.5

• If the image/drawing is given to you from another
  source (e.g. the IB Test?) and you need to
  calculate the magnification you can do so by
  using the scale bar that will be found in the
  picture and by reversing the equation to
• Magnification measured length/actual length
  (based on scale bar)

16
2.1.6

• As the size of a structure increases (e.g. a
  cell), its surface area to volume ratio
  decreases
• This causes problems with growing cells in that
  metabolic process, which occur inside the cell,
  depend upon the materials that the cell membrane
  allows to enter and leave the cell
• Once the ratio reaches a point at which the
  cells volume is more than can be supported by
  the surface area of the cell, the cell must divide

17
2.1.7

• Emergent Properties
• Multicellular organisms show emergent properties
• Emergent properties arise from the interaction of
  component parts
• In other words, the whole is greater than the sum
  of its parts
• The human eye is an excellent example of this

18
2.1.8-9

• Cells in multicellular organisms begin as stem
  cells that are capable of expressing any of the
  genes they contain and therefore performing any
  function for the organism that they are a part of
• These stem cells will eventually differentiate to
  carry out specialized functions for the organism
• This is done by shutting off certain genes
  while allowing others to be expressed (stay on)

19
2.1.8

• Examples of cells that have become differentiated
  for specific purposes include red blood cells,
  skin cells, brain cells, muscle cells, and kidney
  cells

20
2.1.10

• Stem cells are a major topic of modern day
  scientific research
• Because they are undifferentiated they can be
  used to replace any type of body cell needed
• For instance, in 2005, stem cells were used to
  restore the insulation tissue of neurons (brain
  cells) in lab rats, resulting in subsequent
  improvements in their mobility

21
2.1.10

• In humans, an example of the successful use of
  stem cells is the treatment of Non-Hodgkins
  Lymphoma (a type of cancer that destroys the
  lymphatic system)
• Cancer treatment such as radiation and
  chemotherapy can destroy healthy red blood cells
  along with the cancerous lymphatic cells
• Stem cells injected into patients can
  differentiate to become healthy red blood
• Stem Cell Animation
• http//www.dnalc.org/stemcells.html

22
2.1.10

• Stem cell research can be quite controversial,
  however, due to the ethical questions as to how
  to obtain them
• Most commonly, stem cells are obtained from
  embryos
• This can be of major concern for those who feel
  that a life is being destroyed in order to obtain
  the stem cells

23
2.1.10

• Research is being conducted in order to find
  other sources of stem cells (e.g. bone marrow)
• Therapuetic Cloning has been developed to use
  already differentiated cells from a living person
  to create stem cells
• Take a healthy cell from patient
• Insert the nucleus of the healthy cell
  (containing the patients DNA) with an egg cell
  that has had its nucleus removed

24
2.1.10

• Egg cell divides multiple times to form a
  blastocyst (hollow ball of cells) composed of
  totipotent cells (capable of being pushed to
  differentiate into any type of cell)
• Totipotent cells are pushed to differentiate
• Newly developed cells are injected into patient

25
2.2 Prokaryotic Cells

• Chapter 4

26
2.2

• The first types of cells to develop
  evolutionarily were prokaryotes
• The term prokaryote means naked DNA
• Prokaryotes therefore, do not have a nuclear
  membrane surrounding their DNA

27
2.2

• In fact, they have no membrane bound structures
  and are instead very simple in construction
• Prokaryotes began, and continue to be,
  unicellular organisms
• All bacteria are prokaryotes

28
2.2.1
29
2.2.2

• Prokaryotes consist of the following structures
• Plasma Membrane controls what enters and exits
  the cell
• Sometimes has infoldings (called mesosomes) that
  increase the surface area of the membrane

30
2.2.2

• Cell Wall provides protection
• Made of a protein/carbohydrate structure
• Bacteria are identified based upon which of the
  two types of cell walls they have as based upon
  the Gram Stain Technique
• Gram positive bacteria stain purple
• Gram negative bacteria stain pink

31
2.2.2

• Flagella Tail-like structure that helps with
  locomotion
• Pilli Threadlike projections that help with
  attachment and sexual reproduction (through
  transfer of DNA)
• Cytoplasm clear, gelatinous fluid that takes up
  most of the space inside the cell and contains
  all necessary enzymes for metabolic processes

32
2.2.2

• Ribosomes Used for protein synthesis, which is
  a part of gene expression
• Composed of two parts called the heavy and
  light pieces
• Heavy and light pieces are 50s and 30s in size (s
  represents the svedburg unit)
• Total measurement of prokaryotic ribosomes is 70s
  (doesnt add up because s is not a measurement of
  size but sedimentation during centrifugation)

33
2.2.2

• Nucleoid Region where DNA can be found
• In prokaryotes, DNA forms a closed loop
• Many prokaryotes also have a smaller loop called
  a plasmid that contains a few genes and can be
  easily transferred to other cells

34
2.2.3
35
2.2.4

• Conjugation
• Form of reproduction in some prokaryotes
• 2 prokaryotes attach to each other via the pilus
  and exchange genetic material.
• Then go on to binary fission.

NOTE Conjugation does not create new
prokaryotes!! It recombines the DNA before they
go on to divide separately.
36
E. Coli infection http//www.biology.ualberta.ca/
facilities/multimedia/uploads/microbiology/ecoli.h
tml
37
2.2.4

• Binary fission
• Method of reproduction in prokaryotes
• Asexual form of reproduction in which a cell
  divides into two same size cells that are
  genetically identical

38
2.3 Eukaryotic Cells

• Chapter 4

39
2.3

• Eukaryotic Cells evolved after prokaryotes
• The endosymbiotic theory states that eukaryotes
  came about when one prokaryote enveloped another

40
2.3.1

• Eukaryotic Cells are much more complex than
  prokaryotes
• Made up of smaller components with specialized
  functions called organelles

41
2.3.1
42
2.3.1
43
2.3.1
44
2.3.1
45
2.3.2

• Cell Organelles
• Nucleus contains DNA
• Ribosomes create new proteins
• Composed of a 40s and 60s unit which makes the
  ribosome overall to be 80s
• Rough Endoplasmic Reticulum (Rough ER) site
  protein synthesis
• Called rough because it is studded with
  ribosomes

46
2.3.2

• Smooth ER site of lipid (fat) synthesis and
  storage
• Lysosome contains enzymes that break down
  cellular waste
• Golgi Apparatus (aka Golgi Body) packages and
  ships proteins (to other parts of the cell as
  well as outside of the cell)

47
2.3.2

• Mitochondria powerhouse of the cells creates
  energy for the cell in the form of ATP
• Cytoplasm clear gelatinous fluid inside of the
  cell
• Centriole helps with cell division in animal
  cells

48
2.3.2

• Chloroplast found only in plant cells, this
  organelle is the site of photosynthesis
• Cell Wall found only in plant cells, this
  organelle gives support and structure to the cell
• Plasma membrane controls what enters and exits
  the cell

49
2.3.2

• Microtubules and Microfilaments linear protein
  structures that provide support for animal cells
  sometimes aid in movement of cell organelles
• Nucleolus found within the nucleus, this
  organelle is in charge of creating new ribosomes
• Vacuole stores food, water, and/or waste
  animal cells have multiple small ones while plant
  cells have one large vacuole for water storage
  only

50
2.3.4
Prokaryotes Eukaryotes
No membrane bound organelles DNA is in the cytoplasm (nucleoid region) DNA is naked has no associated proteins No centrioles No mitochondria 70s ribosome All ribosomes are free Cell wall is made of peptidoglycans Multiple membrane bound organelles including the nucleus, which houses DNA DNA is associated with proteins that help it to fold into chromosomes Centrioles Mitochondria 80s ribosome Free ribosomes and ribosomes attached to the rough er No cell wall or one made of cellulose
51
Proteins associated with DNA
52
Comparing Prokaryotes and Eukaryotes http//www.b
iology.ualberta.ca/facilities/multimedia/uploads/c
ell_biology/provseuk.html
53
2.3.5

• Plant and animal cells are very similar but have
  a few distinct differences

Plant Cells Animal Cells
Cell Wall One large vacuole No centrioles Has chloroplasts Store energy as starch No cell wall Many small vacuoles Has centrioles No chloroplasts Store energy as glycogen
54
Animal Cell Mix-Match http//www.biology.ualberta
.ca/facilities/multimedia/uploads/cell_biology/ani
malcell_DD.html Plant Cell Mix-Match http//www.
biology.ualberta.ca/facilities/multimedia/uploads/
cell_biology/plantcell_DD.html
55
Starch vs. Glycogen
56
2.3.5
57
2.3.6

• Roles of extracellular components
• Plant cell wall mantains cell shape, prevents
  excessive water uptake, and holds the whole plant
  up against the force of gravity
• Animal cells secrete glycoproteins that integrate
  themselves in the plasma membrane
• The glycoproteins help with support, adhesion and
  movement

58
2.4 Membranes

• Chapter 5

59
2.4.2

• The membranes of eukaryotic cells and their
  organelles are complex in structure
• Basic membrane is a phospholipid bilayer
• Two layers of phosopholipids
• Phospholipids are molecules that consist of a
  hydrophilic (water loving) phosphate group
  head and a hydrophobic (water fearing) lipid
  tail
• Phosphate groups are therefore on the edges of
  the membrane while the lipid tails form the inner
  portion

60
2.4.2
P 57
61
2.4.2
Hydrophilic Phosphate groups
Hydrophobic Lipid tails
Hydrophilic Phosphate groups
62
2.4.3

• Cholesterol and proteins are embedded within the
  plasma membrane
• Cholesterol - binds together lipids in plasma
  membrane, reducing fluidity spaces lipids,
  preventing solidification.
• Integral Proteins Span from one side of the
  phospholipid bilayer to the other
• Peripheral proteins attached to the surface of
  the membrane
• Glycoproteins found on outside of bilayer
  involved in cell recognition (immune sys) or cell
  communication (hormones)

63
2.4.1
64
2.4.3

• Functions of membrane proteins
• Hormone binding sites glycoproteins outside of
  membrane
• Immobilized enzymes peripheral on the inside
  of the membrane
• Cell adhesion peripheral on the outside of the
  membrane

65
2.4.3

• Cell-to-cell communication (glycoproteins,
  outside of membrane)
• Channels for passive (non-energy requiring)
  transport of materials across the cell membrane
  (integral membrane proteins)
• Protein pumps for active (energy requiring)
  transport of materials across the membrane
  (integral membrane proteins)
• Note The phospholipid bilayer only allows O2,
  CO2, and H2O to cross without the aid of membrane
  proteins. Because of this, it is sometimes
  referred to as being semi-permeable

66
2.4.4

• Diffusion and Osmosis
• Diffusion refers to the passive movement of
  particles from an area of high concentration to
  an area of low concentration
• e.g. gas leaks and perfume

67
2.4.4

• Osmosis is a specific type of diffusion
• The diffusion of water across a semi-permeable
  membrane (e.g. the plasma membrane) from an area
  of lower solute concentration to an area of
  higher solute concentration
• solute refers to the substance that is dissolved
  in the water (e.g. salt)

68
2.4.4

• There are three types of osmotic solutions
• Isotonic solute concentration is the same
  inside the cell as outside the cell
• Equal amount of water crossing in and out
• Cell stays the same shape

69
2.4.4
70
2.4.4

• Hypertonic solute concentration is higher
  outside the cell than inside the cell(which means
  the water concentration is lower outside the cell
  than inside)
• Water moves out of the cell
• Plasma membrane shrinks
• One example of this is plants wilting

71
2.4.4
72
2.4.4

• Hypotonic solute concentration is lower outside
  the cell than inside (which means water
  concentration is higher outside than inside)
• Water moves into the cell
• Plasma membrane swells
• Can sometimes cause animal cells to burst

73
2.4.4
74
2.4.4
75
2.4.5

• Passive Transport
• Passive transport refers to the movement of
  molecules down the concentration gradient (high
  conc -gt low conc)
• Passive transport does not require energy
• Two types simple diffusion and facilitated
  diffusion

76
2.4.5

• Simple diffusion refers to the passive diffusion
  of molecules across the membrane without the aid
  of proteins (e.g. water, oxygen, carbon dioxide)
• Facilitated diffusion refers to the passive
  diffusion of molecules through channel proteins

77
2.4.6

• Active Transport
• Refers to the transport of molecules across the
  membrane against the concentration gradient (low
  conc -gt high conc)
• Requires energy in the form of ATP
• Transport is carried out by protein pumps
  (specialized integral proteins)

78
2.4.6

• Transported molecules enter the protein pump
• The release of energy from ATP causes a shape
  change in the protein that then allows the
  molecule to move through

79
2.4.7

• Molecules are transported within the cell via
  vesicles
• Primary example is the transport of proteins
• Proteins are synthesized by ribosomes in the
  rough er

Vesicles are essentially circular lipid membranes
80
2.4.7

• Newly made proteins are packaged in vesicles and
  sent to the Golgi Apparatus where they fuse with
  the membrane
• Proteins are modified and repackaged into
  vesicles
• Vesicles travel to the cell membrane where they
  fuse, thus releasing the protein in the
  extracellular fluid (process called exocytosis)

81
2.4.7
82
2.4.8

• Exocytosis and Endocytosis
• As mentioned previously, exocytosis is the fusing
  of a vesicle from inside the cell with the cell
  membrane
• Purpose is to release a molecule made in the cell
  to the extracellular fluid

83
2.4.8
84
2.4.8

• Endocytosis is pinching in of the plasma membrane
  to create a vesicle that contains molecules from
  the extracellular environment
• This is how the cell obtains its nutrients

85
2.4.8

• The ability of vesicles to fuse with the plasma
  membrane is due to the fluidity of its lipid
  structure (remember, though, the more
  cholesterol, the less fluid the membrane is)
• Exocytosis enlarges the size of the plasma
  membrane
• This is balanced by endocytosis, which reduces
  the size plasma membrane

86
2.4.8
87
2.5 Cell Division

• Chapter 9

88
2.5.1

• The cells life cycle (usually just called the
  cell cycle) consists of two main parts
• Interphase active period in the life of a cell
  when many metabolic reactions occur, including
• protein synthesis
• DNA replication
• an increase in the number of mitochondria and/or
  chloroplasts (2.5.3)
• Mitosis cell divides

89
2.5.1

• Interphase can be divided into three phases
• G1 cell grows and metabolizes
• S DNA is replicated
• G2 cell prepares for division

90
2.5.1

• Mitosis can be divided into four stages
• Prophase
• Metaphase
• Anaphase
• Telophase

91
2.5.1
92
2.5.2

• Sometimes the gene controlling cell division
  (called an oncogene) will become mutated
• The result is that cell division continues
  repeatedly
• This is how tumors are formed
• Tumors can form in any tissue of the body

Stomach Tumor
93
2.5.4

• Prophase
• Nuclear envelope disappears
• With the aid of special proteins called histones,
  DNA supercoils into distinct chromosomes that are
  visible under the microscope
• Each pair of identical segments of DNA, called
  sister chromatids, bind together at the
  centromere to form one chromosome

94
2.5.4
95
2.5.4

• Centrioles moved to opposite ends of the cell
• Long, tubular proteins called spindle fibers
  grow from the centrioles and attach to the
  centromeres of the chromosomes

96
2.5.4

• Metaphase
• Spindle fibers pull chromosomes to the equator
  (center line) of the cell

97
2.5.4

• Anaphase
• Spindle fibers shorten
• Sister chromatids are pulled apart and are now
  called chromosomes
• Chromosomes are pulled to opposite ends of the
  cell

98
2.5.4

• Telophase
• Reverse of prophase
• Spindle fibers dissapear
• DNA uncoils and becomes chromatin
• Nuclear envelope reforms

99
2.5.4

• Cytokinesis
• Splitting of the cytoplasm
• Occurs when microtubule proteins pinch inward at
  the equator (cleavage furrow)
• Results in two separate but identical cells

100
2.5.4

• In plants a cell plate forms instead of a
  cleavage furrow

101
2.5.4
102
2.5.5

• Mitosis produces two genetically identical nuclei
• During the S phase of interphase DNA is
  replicated to produce two identical copies
• During prophase the identical copies of each
  chromosome (homologous chromsomes) bind together
• Homologous chromosomes are pulled apart during
  anaphase and become part of two separate nuclei
  during telophase

103
2.5.6

• Mitosis serves many purposes
• Tissue/organ growth
• Embryonic devleopment, when the zygote divides to
  produce many smaller cells
• Tissue damage and repair
• Asexual reproduction (unicellular organisms)