Cells

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Cells

• Topic 2

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Cell Theory

• Schleiden, Schawnn, and Virchow
• Three components
• All living things are made of cells.
• Cells are the basic unit of structure and
  function in living organisms.
• Cells come from other cells.

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Cells are microscopic

• Most cells cant be seen without a microscope
• Smallest cells are bacteria with diameters as
  small as .2 um.
• The bulkiest cells are bird eggs
• Longest human cells are certain muscle and nerve
  cells.
• Most plant and animal cells (10 to 100 um)are ten
  times larger than most bacteria
• Refer to figure 4.2A on p. 54

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Surface area to volume ratio of cells

• The max. size of a cell is influenced by its
  requirement for enough surface area to obtain
  adequate nutrients and oxygen from the
  environment and dispose of wastes.
• Cells must be very tiny to ensure the surface
  area is much larger than the volume for
  efficiency in a cell.

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Prokaryotic Cells

• Bacteria and Archaebacteria
• Very small cells, can only be seen with electron
  microscope
• Range from 1 to 10 um in length, about 1/10 the
  size of a eukaryotic cell
• Lack a nucleus and membrane bound organelles.
• DNA is coiled in a nucleoid
• Have ribosomes, cell wall, capsule, pili, and
  flagella
• Reproduce asexually via binary fission

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Prokaryotic cells

• Cell Wall
• Protects the cell and gives it shape
• Capsule
• Surrounds the cell wall and further protects the
  cell surface
• Pili
• Short projections used to attach bacteria to
  each other
• Flagella
• Longer projections used for movement
• Ribosomes
• Synthesize proteins

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Eukaryotic Cells

• Protists, Fungi, Plants, and Animals
• Have nucleus and membrane-bound organelles
• Much larger and more complex than prokaryotic
  cells.
• Reproduce sexually and asexually

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Eukaryotic OrganellesGeneral Function
Manufacturing

• Nucleus
• Control center of cell contains most of the
  cells DNA
• Nucleolus
• Location where ribosomes are synthesized
• Nuclear pore
• Allows RNA to move in and out of nucleus

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• Ribosomes
• Protein synthesis
• Rough ER
• Comprised of a network of tubes and flattened
  sacs.
• Continuous with plasma membrane and nuclear
  membrane
• Site of protein synthesis (consists of ribosomes)

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Eukaryotic OrganellesGeneral Function
Manufacturing

• Smooth ER
• Site of lipid and carbohydrate metabolism
• No ribosomes
• Golgi Apparatus
• Connected with ER flattened disc-shaped sacs,
  stacked one on top of the other
• Modification, storage, and packaging of proteins.
• tags proteins so they go to the correct
  destination.

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Eukaryotic OrganellesGeneral Function Breakdown

• Lysosomes (in animal cells and some protists)
• Digestion of nutrients, bacteria, and damaged
  organelles destruction of certain cells during
  embryonic development
• Peroxisomes
• Diverse metabolic processes with breakdown of
  H2O2 by-product
• Vacuoles
• Digestion (like lysosomes) storage of chemicals,
  cell enlargement water balance

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Eukaryotic OrganellesGeneral Function Energy
Processing

• Chloroplasts
• Conversion of light energy to chemical energy of
  sugars (site of photosynthesis)
• Mitochondria
• Conversion of chemical energy of food to chemical
  energy of ATP
• Power House of cell
• Bound by double membrane

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Eukaryotic OrganellesGeneral Function Support,
Movement, and Communication

• Cytoskeleton (including cilia, flagella, and
  centrioles in animal cells)
• Maintenance of cell shape anchorage for
  organelles movement of organelles within cells
  cell movement mechanical transmission of signals
  from exterior of cell to interior.
• Cell walls (in plants, fungi, and protists)
• Maintenance of cell shape and skeletal support
  surface protection binding of cells in tissues

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Eukaryotic OrganellesGeneral Function Support,
Movement, and Communication

• Extracellular matrix
• Binding of cells in tissues surface protections
  regulation of cellular activities
• Cell junctions
• Communication between cells binding of cells in
  tissues.

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Cell Membranes

• Membranes provide the structural basis for
  metabolic order.
• In eukaryotes, most organelles are made from
  membranes
• Many enzymes are built right into the membranes
  of these organelles

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Selective permeability

• Cell membranes control what goes in and out of
  the cell
• It allows some substances to cross more easily
  than others
• Cell membrane is amazingly thin

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Membrane phospholipids form a bilayer

• Lipids, mainly phopholipids, are the main
  structural components of membranes
• Phospolipid has a phosphate group and only two
  fatty acids
• Head, with a charged phosphate group, is
  hydrophillic
• Fatty acid tails are nonpolar and hydrophobic
• Thus, the tail end is pushed away by water, while
  the head is attracted to water

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Phospholipid Bilayer

• Phospholipids form a two-layer sheet called a
  phospholipid bilayer.
• Hydrophillic heads face outward, exposed to the
  water on both sides of a membrane
• Hydrophobic tails point inward, mingling together
  and shielded from water.

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Phospholipid Bilayer
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Phospholipid bilayer

• Hydrophobic interior of the bilayer is one reason
  membranes are selectively permeable.
• Nonpolar, hydrophobic molecules are lipid-soluble
  can easily pass through membranes
• Polar molecules and ions are not lipid-soluble
• Ability to pass through membrane depends on
  protein molecules in the phospholipid bilayer.

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Fluid Mosaic Model

• Plasma membrane is described as a Fluid Mosaic
• Mosaic denotes a surface made of small fragments,
  like pieces of colored tile
• A membrane is considered mosaic because it has
  diverse protein molecules embedded in a farmework
  of phospholipids.
• A membrane mosaic is fluid in that most of the
  individual proteins and phospholipids can can
  drift literally in the membrane

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• Tails of phospholipids are kinked.
• Kinks make the membrane more fluid by keeping
  adjacent phospholipids from packing tightly
  together.
• In animal cells, the steroid cholesterol
  stabilize the phospholipids at body temperature
  and also keep the membrane fluid at lower
  temperatures.
• In a cell, phospholipid bilayer remains about as
  fluid as salad oil at room temperature.

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• Outside surface of plasma membrane has
  carbohydrates bonded to proteins and lipids in
  the membrane.
• A protein with attached sugars is called a
  glycoprotein, whereas a lipid with sugars is
  called a glycolipid.
• Function as cell identification tags that are
  recognized by other cells.
• Significant for cells in an embryo to sort
  themselves to tissues and organs.
• Also functions in the immune system to recognize
  and reject foreign cells.

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Proteins make the membrane a mosaic of function

• Mosaic refers both to positioning of proteins in
  membrane but also the activities of these
  proteins.
• Proteins perform most of the functions of a
  membrane.
• Different cells contain different sets of
  membrane proteins, and membranes within cells
  have unique proteins

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Functions of Membrane Proteins

• Attaching the membrane to cytoskeleton and
  external fibers
• Providing identification tags
• Forming junctions between adjacent cells
• Enzymes, functioning in catalytic teams for
  molecular assembly lines
• Receptors for chemical messengers from other
  cells
• Help move substances across the membrane, like
  water and glucose

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Receptor proteins

• Has a shape that fits the shape of a specific
  messenger, such as a hormone, just as an enzyme
  fits its substrate
• Binding of messenger to the receptor triggers a
  chain reaction involving other proteins, which
  relay the message to a molecule that performs a
  specific activity inside the cell (signal
  transduction)

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Passive Transport

• Diffusion of a substance across a biological
  membrane
• Diffusion is the movement of particles from high
  concentration to low concentration.
• Moves with a concentration gradient
• No energy input required
• Eventually reaches equilibrium
• Molecules continue to move back and forth, but no
  net change in concentration will occur

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Passive Transport

• Necessary in our cells lungs transport oxygen in
  red blood cells and carbon dioxide out via
  diffusion.
• Small, nonpolar molecules that easily diffuse
  across plasma membranes

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Passive Transport Facilitated Diffusion

• Facilitated diffusion
• Many substances cant diffuse freely across
  membrane because of their size, polarity, or
  charge
• Need the help of specific transport proteins in
  the membrane to move across the membrane
• Does not require energy
• Goes with the concentration gradient (high to
  low)
• Some sugars, amino acids, ions, and even water
  use facilitated diffusion
• Since water is polar, movement through
  hydrophobic interior is slow. Aquaporins allow
  for rapid transport into and out of cell.

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Passive Transport Facilitated Diffusion

• Transport proteins (figure 5.15)
• Have to be specific to molecule moving across the
  membrane
• One example provides a pore, or tunnel, for the
  passage of a solute
• Another example protein binds molecule, changes
  shape, and releases molecule on the other side

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Passive Transport Osmosis

• Osmosis Diffusion of water molecules across a
  selectively permeable membrane
• With concentration gradient
• Requires no energy
• Tonicity
• Describes the tendency of a cell in a given
  solution to lose or gain water.
• Isotonic, hypertonic, and hypotonic

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Passive Transport Osmosis

• Isotonic solution
• Equal concentration of solvent inside and outside
  of cell water goes in and out
• Cells volume remains the same equilibrium
• Hypertonic solution
• Solute concentration is lower inside cell
  (solvent concentration is higher inside cell)
  Water goes out
• Cell shrivels
• Causes plasmolysis in plant cells

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Passive Transport Osmosis

• Hypotonic solution
• Solute concentration is greater inside the cell
  (solvent concentration is lower inside the cell)
  water goes in
• Cell swells and may lyse
• Causes cytolysis in animal cells
• Refer to figure 5.17

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Passive Transport Osmosis

• Osmoregulation
• Control of water balance
• Method by which animals survive in hypertonic and
  hypotonic environments
• Example freshwater fish have kidneys and gills
  that work constantly to prevent excessive buildup
  of water in the body

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Active Transport

• Requires that a cell expend energy to move
  molecules across a membrane
• Moves against the concentration gradient.
• ATP supplies the energy
• Moving molecules from low to high concentration

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Active transport

• Simple model, figure 5.18
• Process begins when solute on cytoplasmic side of
  the plasma membrane attaches to a specific
  binding site on the transport protein.
• ATP phoshporylates the transport protein
• Causing it to change shape in such a way that the
  solute is released on the other side of the
  membrane
• Phosphate group detaches and the transport
  protein returns to its original shape

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Active Transport
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Active Transport Exocytosis

• Exocytosis
• Used to export bulky materials
• Examples insulin secretion into blood from
  pancreas tear glands secrete salty soln
  containing proteins
• A membrane-enclosed vesicle filled with
  macromolecules moves to the plasma membrane
• Vesicle fuses with plasma membrane
• Vesicles contents spill out of the cell

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Endocytosis

• Endocytosis
• A cell takes in macromolecules or other particles
  by forming vesicles or vacuoles from its plasma
  membrane
• Three kinds phagocytosis, pinocytosis,
  receptor-mediated endocytosis

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Endocytosis

• Phagocytosis
• cellular eating
• Molecules of food move into the cell
• Example amoeba
• Pinocytosis
• cellular drinking
• Molecules of fluid move into the cell not
  specific
• Receptor-mediated endocytosis
• Highly specific materials come in through
  indented pit in plasma membrane. Pit is lined
  with receptor proteins, pinch close to form
  vesicle containing molecules to be brought into
  the cell
• Example cholesterol

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Summary of Cell Transport
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Cell Division

• Cell Division
• Virchow Cells can only come from preexisting
  cells
• In unicellular organisms, can reproduce an entire
  organism
• Allows multicellular organisms to reproduce
  asexually
• Basis of sexual reproduction? sperm and egg
• Allows fertilized egg, or zygote, to develop into
  an adult organism
• Replaces worn-out or damaged cells
• Enables multicellular organism to grow to adult
  size

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Prokaryotes reproduce by binary fission

• Binary fission
• Process by prokaryotes reproduce by cell
  division.
• Steps
• Duplication of chromosomes and separation of
  copies.
• Cell elongates
• Divides into two daughter cells

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Chromosomes

• Human cells carry about 20,000 genes to make
  100,000 proteins.
• Almost all genes are located in the nucleus
• Very small amount found in mitochondria
• Genes are found on DNA
• Chromatin
• Diffuse mass of long, thin fibers, not seen under
  the microscope, less tightly coiled
• Combination of DNA and protein

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Chromosomes

• Chromosomes
• Rod-shaped structure
• Coiled up, compact forms of chromatin
• Contains one long DNA molecule bearing hundreds
  or thousands of genes.
• DNA is attached to protein molecules (histones)
• Sister chromatids
• Each duplicated chromosome contains two identical
  copies.
• Centromere
• The point by which two chromatids are joined.

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• What is the difference between diploid and
  haploid and what are those numbers in humans?
• Diploid 2 sets of chromosomes (2n) 46 in humans
• Haploid 1 set of chromosomes (n) 23 in humans

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• What is the process called in Eukaryotes, when
  cells divide to make cells exactly alike
  (diploid)?
• Mitosis!
• What is the process called in Eukaryotes, when
  cells divide to make haploid cells?
• Meiosis!

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Cell Cycle

• In your own body, millions of cells must divide
  every second to maintain the total number of
  about 100 trillion cells.
• Some cells divide once a day, and some do not at
  all (mature muscle cells, liver cells, brain
  cells)

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Interphase

• Occurs when the cell is between cell division
• Interphase stages
• G1 Cells grow to mature size
• S DNA is copied
• G2 Cell prepares for division
• Cells exit the cell cycle via
• G0 Cells do not copy DNA or prepare for
  mitosis, but are still alive (e.g. nervous
  system)

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Interphase
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Prophase

• What does the cell look like?
• Centrioles and spindle fibers appear
• Nuclear envelope disappears, and chromosomes are
  visible

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Prophase

• What happens to the DNA and nucleus?
• Chromosomes form when chromatin tightens and
  coils
• Nuclear membrane breaks down and disappears
• What two things appear near where the nucleus
  was?
• Centrioles and spindle fibers

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Prophase
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Metaphase

• What does the cell look like?
• Chromosomes move to the middle
• Where are the chromosomes during metaphase?
• Middle of the cell

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Metaphase
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Anaphase

• What does the cell look like?
• Chromosomes move to the end of cell
• What happens to the chromosomes?
• Chromosome splits at centromere into 2 chromatids
  and moves to end of cell

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Anaphase
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Telophase

• What does the cell look like?
• Cell starts to pinch in
• Nucleus starts to reform
• Chromosomes are at opposite ends
• What happens to the chromosomes and nucleus?
• Nucleus forms back around single chromatids

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Telophase
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After Telophase

• What is cytokinesis?
• Cytoplasm and contents (other organelles) divide
• Whats special about cytokinesis in plants?
• Cell wall also divides with new cell plate in
  middle

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Growth Factors signal the cell cycle

• Growth factors are the main signals that
  stimulate cell division
• Cells have a series of checkpoints that are
  regulated by proteins.
• These checkpoints determine whether or not cell
  division will occur.

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Cancer

• Mutations in the genes of these checkpoint
  proteins may lead to cancer
• The uncontrolled growth of cells.
• Tumor an abnormally growing mass of body cells
• Benign tumor
• If abnormal cells remain at original site
• Can be problematic if disrupt certain organs, but
  usually easily removed by surgery
• Malignant tumor
• If abnormal cells spread into other tissues and
  body parts, interrupting organ function

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Cancer

• Metastasis
• Cancer that spreads via the circulatory system
• Carcinomas
• Cancer found in the external or internal
  coverings of the body skin, lining of intestine
• Sarcomas
• Cancer found in tissues that support the body
  bone and muscle
• Leukemias and lymphomas
• Cancer of blood forming tissues, bone marrow,
  spleen, and lymph nodes

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Cancer

• Usually caused by a loss of inhibitory factors
  (tumor suppressor genes), or an increase in
  growth factors (oncogenes).
• Surgery, radiation, and chemotherapy are typical
  treatments

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Cell Differentiation

• During repeated cell division that lead from a
  zygote to a multicellular adult, individual cells
  must undergo differentiation
• Become specialized in structure and function
• Results from selective gene expression, the
  turning on and off of genes
• Each differentiated cell expresses genes that
  allow the cell to perform certain functions
• Beta cells expressed genes that allow it to
  produce the hormone insulin

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Cell Differentiation

• About 50 cell division produce approximately 100
  billion cells in an adult.
• During the development of an embryo, the cells
  specialize to take on the roles of 220 different
  cell types.
• Some cells stop dividing at a certain point in
  the adult life, some continue to divide
  throughout lifespan
• Genes, either turned on or off, control the
  destined role of the cell.

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Stem Cells

• Adult Stem Cells (ACS)
• Cells present in adult tissues that generate
  replacemetns for nondividing diffrentiated cells.
• multipotent
• Embryonic Stem Cells (ES cells)
• Harvested from the blastocyst
• Give rise to all the different kinds of
  specialized cells of the body
• pluripotent

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Stem Cells

• Induced Pluripotent Stems Cells (iPS)
• Stem cells created via de-differentiation of an
  adult cell (eg. Skin cell).
• Pluripotent

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Cloning

• Nuclear transplantation is used
• Replacing nucleus of an egg cell or zygote with
  the nucleus of an adult somatic cell.
• After sever days, a blastocyst forms which may be
  used for many purposes
• If stem cells in blastocyst are used for the
  birth of a new individual reproductive cloning
• Can be used to create genetically identical
  individuals for experimentation.
• If stem cells in blastcyst are induced to form
  specialized cells therapeutic cloning
• Used to make essential cells beta cells to make
  insulin, dopamine neurons for Parkinsons
  patients.