Cell Structure and Function

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Chapter 3

• Cell Structure and Function

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What does the cell theory tell us?
3.1 What is a cell?

• A cell is the basic unit of life
• All living things are made up of cells
• New cells arise from preexisting cells

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Cellular Organization

• Cell smallest living unit
• Performs all life functions

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Why are most cells small?
3.1 What is a cell?

• Consider the cell surface-area-to-volume ratio
• Small cells have a larger amount of surface area
  compared to the volume
• An increase in surface area allows for more
  nutrients to pass into the cell and wastes to
  exit the cell more efficiently
• There is a limit to how large a cell can be and
  be an efficient and metabolically active cell

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Thinking about surface area to volume in a cell
3.1 What is a cell?
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What are some common microscopes used to view
cells?
3.1 What is a cell?

• Compound light microscope
• Lower magnification
• Uses light beams to view images
• Can view live specimens
• Transmission electron microscope
• 2-D image
• Uses electrons to view internal structure
• High magnification, no live specimens
• Scanning electron microscope
• 3-D image
• Uses electrons to view surface structures
• High magnification, no live specimens

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What are the two major types of cells in all
living organisms?
3.2 How cells are organized

• Prokaryotic cells
• Thought to be the first cells to evolve
• Lack a nucleus
• Represented by bacteria and archaea
• Eukaryotic cells
• Have a nucleus that houses DNA
• Many membrane-bound organelles

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What do prokaryotic and eukaryotic cell have in
common?
3.2 How cells are organized

• A plasma membrane that surrounds and delineates
  the cell
• A cytoplasm that is the semi-fluid (cytosol)
  portion inside the cell that contains organelles
• DNA

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Where did eukaryotic cells come from?
3.2 How cells are organized
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Eukaryotic Cell
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Two Categories of Cells

• Sex cells (germ cells)
• reproductive cells
• male sperm
• female oocytes (eggs)
• Somatic cells (soma body)
• all body cells except sex cells

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Organelle Functions
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Organelle Functions
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The structures and functions of the cell
membrane.
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Plasma Membrane Components

• Phospholipid bilayer
• Cholesterol resist osmotic lysis
• Carbohydrates
• Proteins

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Functions of Plasma (Cell) Membrane

• Physical barrier
• Maintain homeostasis
• Separates intracellular fluid from extracellular
  fluid, different conditions in each
• Regulates exchange with environment
• ions and nutrients enter
• waste and cellular products released
• Monitors the environment
• extracellular fluid composition
• Cell communication and signaling
• Structural support
• anchors cells and tissues

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Plasma Membrane Components

• 1. Phospholipid Bilayer
• hydrophilic headstoward watery environment, both
  sides
• hydrophobic fatty-acid tailsinside membrane
• barrier to ions and water soluble compounds
• 2. Cholesterol resist osmotic lysis

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Plasma Membrane Components

• 3. Carbohydrates
• -linked to other molecules as proteoglycans,
  
• glycoproteins, and glycolipids
• -Functions
• -lubrication protection
• -anchoring locomotion
• -binding specificity
• (acts as receptor)
• -self recognition

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Plasma Membrane Components

• 4. Protein
• ½ mass of membrane
• Integral proteins span width of membrane
• within the membrane
• Peripheral proteins
• Adhere to inner or outer surface of the membrane

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6 Functions of Membrane Proteins

• Anchoring proteins (stabilizers)
• attach to inside or outside structures
• Recognition proteins (identifiers)
• Self identification by immune system
• Label cells normal or abnormal
• Enzymes
• catalyze reactions in cytosol in extra cellular
  fluid
• Receptor proteins
• bind and respond to ligands (ions, hormones) or
  signaling, or import/export
• Carrier proteins
• transport specific solutes through membrane
• Channels
• regulate water flow and solutes through membrane

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How things get in and out of cells.
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Overcoming the Cell Barrier

• The cell membrane is a barrier, but
• nutrients must get in
• products and wastes must get out
• Permeability determines what moves in and out of
  a cell
• A membrane that
• lets nothing in or out is impermeable
• lets anything pass is freely permeable
• restricts movement is selectively permeable

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Selective Permeability

• Cell membrane is selectively permeable
• allows some materials to move freely
• restricts other materials
• Restricts materials based on
• size
• electrical charge
• molecular shape
• lipid solubility

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Selectively Permeable
3.3 The plasma membrane and how substances cross
it
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How do things move across the plasma membrane?
3.3 The plasma membrane and how substances cross
it

• 1. Diffusion
• 2. Osmosis
• 3. Facilitated transport
• 4. Active transport
• 5. Endocytosis and exocytosis

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Solutions

• All molecules are constantly in motion
• Molecules in solution move randomly
• Random motion causes mixing

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Concentration Gradient

• Concentration is the amount of solute (glucose)
  in a solvent (e.g. H20)
• Concentration gradient
• more solute in 1 part of a solvent than another
• Function Diffusion
• molecules mix randomly
• solute spreads through solvent
• eliminates concentration gradient
• Solutes move down a concentration gradient
• From high concentration to low concentration

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What are diffusion and osmosis?
3.3 The plasma membrane and how substances cross
it

• 1. Diffusion is the random movement of molecules
  from a higher concentration to a lower
  concentration
• 2. Osmosis is the diffusion of water molecules

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How does tonicity change a cell?
3.3 The plasma membrane and how substances cross
it

• Hypertonic solutions have more solute than the
  insideof the cell and lead to lysis (bursting)
• Hypotonic solutions have less solute than the
  inside of the cell and lead to crenation
  (shriveling)
• Isotonic solutions have equal amounts of solute
  inside and outside the cell and thus does not
  affect the cell

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What are facilitated diffusion and active
transport?
3.3 The plasma membrane and how substances cross
it

• 3. Facilitated transport is the transport of
  molecules across the plasma membrane from higher
  concentration to lower concentration via a
  protein carrier
• 4. Active transport is the movement of molecules
  from a lower to higher concentration using ATP as
  energy requires a protein carrier

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Transport Vesicles
3.3 The plasma membrane and how substances cross
it

• 5. Endocytosis transports molecules or cells into
  the cell via invagination of the plasma membrane
  to form a vesicle
• 6. Exocytosis transports molecules outside the
  cell via fusion of a vesicle with the plasma
  membrane

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Receptor-Mediated Endocytosis
Figure 321
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Pinocytosis

• Pinocytosis (cell drinking)
• Endosomes drink extracellular fluid and enclose
  it in membranous vesicles at the cell surface
• Similar to the steps in receptor-mediated
  endocytosis, except that ligand binding is not
  the trigger

Figure 322a
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Phagocytosis

• Phagocytosis (cell eating)
• pseudopodia (psuedo false, podia feet)
• engulf large objects in phagosomes

Figure 322b
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Cytoskeleton

• A series of proteins that maintain cell shape as
  well as anchors and/or moves organelles in the
  cell
• Made of 4 fibers
• Large microtubules
• Forms the foundation of the cytoskeleton
• Allows the cell to change shape and assists in
  mobility
• Thin actin filaments
• provide additional strength by attaching the
  membrane to the cytoplasm
• Attach integral proteins to cytoskeleton
• Pairs with thick filaments of myosin for muscle
  movement
• Medium-sized intermediate filaments
• strengthen cell and maintain shape
• stabilize position of organelles

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Cilia and Flagella
3.5 The cytoskeleton and cell movement

• Made of microtubules
• Cilia are about 20x shorter than flagella
• Cilia Short, numerous
• Function sweep substances over cell surface
• Flagella Long, singular
• Function propel cell through environment

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Structures involved in protein production
3.4 The nucleus and the production of proteins

• Nucleus
• Ribosomes
• Endomembrane system

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The structure and function of the nucleus
3.4 The nucleus and the production of proteins

• Nucleus
• largest organelle
• Nuclear envelope
• double membrane around the nucleus, connected to
  ER
• Nuclear pores with regulator proteins
• Control exchange of materials between cytoplasm
  and nucleus

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Within the Nucleus

• Nucleoplasm
• fluid containing ions, proteins (enzymes), DNA,
  RNA, and nucleoli
• Nucleoli Dark areas
• site of rRNA synthesis and packaging into
  ribosomal subunits
• In non-dividing cells DNA is loose ? Called
  chromatin
• During Nuclear Division
• Chromatin is tightly coiled into visible
  chromosomes (23 pairs in humans)
• Chromosomes
• tightly coiled DNA (cells dividing)

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The structure and function of ribosomes
3.4 The nucleus and the production of proteins

• Organelles made of RNA and protein
• Found bound to the endoplasmic reticulum and free
  floating in the cell
• Site of protein synthesis

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The Endomembrane System
3.4 The nucleus and the production of proteins

• A series of membranes in which molecules are
  transported in the cell
• It consists of the nuclear envelope, endoplasmic
  reticulum, Golgi apparatus, lysosomes and
  vesicles

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How does the endomembrane system function and
appear?
3.4 The nucleus and the production of proteins
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The parts of the endomembrane system

• Rough endoplasmic reticulum studded with
  ribosomes used to make proteins
• Smooth endoplasmic reticulum lacks ribosomes
  but aids in making carbohydrates and lipids
• Golgi apparatus flattened stacks that process,
  package and deliver proteins and lipids from the
  ER
• Phosphate, carbohydrates, or lipids are attached
• Lysosomes membranous vesicles made by the Golgi
  that contain digestive enzymes
• Vesicles small membranous sacs used for
  transport

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Mitochondria
3.6 Mitochondria and cellular metabolism

• A highly folded organelle in eukaryotic cells
• Produces energy in the form of ATP
• They are thought to be derived from an engulfed
  prokaryotic cell

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Mitochondrial Function Power House of the Cell

• Aerobic respiration occurs on surface of cristae
• takes chemical energy from food (glucose)
• With the use of oxygen, Glucose is catabolized
  creating CO2 waste to convert ADP into ATP
• Mitochondria supply most of cells energy
• Have their own DNA (maternal)
• Can replicate independent of the cell

glucose oxygen ADP carbon dioxide
water ATP
Figure 39b
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Carbohydrate Catabolism (Metabolism)

• Carbohydrates are the primary source of cellular
  energy for most organisms
• Glucose is the most commonly used carbohydrate
  and will always be used first
• Generates ATP and other high-energy compounds by
  breaking down carbohydrates
• glucose oxygen ? carbon dioxide water ?

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Carbohydrate Catabolism (Metabolism)

• Two methods for ATP productions via catabolism of
• glucose
• Cellular Respiration ? Aerobic reactions
• Requires oxygen to serve as the final electron
  acceptor
• Generate ATP in ETC
• Most efficient method of ATP production
• 1 glucose generates 36 ATP
• Involves reaction performed inside the
  mitochondria
• Fermentation ? Anaerobic reactions
• Requires an organic molecule (carbon based) to
  serve as the final electron acceptor
• Can be done in the absence of oxygen
• ATP is synthesized using glycolysis
• Less efficient, 1 glucose generates 2 ATP
• In humans, results in lactic acid

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Enzymes are important for cellular respiration
and many activities in the cell
3.6 Mitochondria and cellular metabolism

• Most enzymes are proteins
• Enzymes are often named for the molecule that
  they work on or substrates
• Enzymes are specific to what substrate they work
  on
• Enzymes have active sites where a substrate binds
• Enzymes are not used up in a reaction but instead
  are recycled
• Some enzymes are aided by non-protein molecules
  called coenzymes

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How do enzymes work?
3.6 Mitochondria and cellular metabolism
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What is cellular respiration?
3.6 Mitochondria and cellular metabolism

• Production of ATPin a cell
• Includes
• Glycolysis
• Citric acid cycle
• 3. Electron transport chain

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What happens in glycolysis step 1 of cellular
respiration?
3.6 Mitochondria and cellular metabolism

• Glycolysis
• Occurs in the cytoplasm
• Breaks glucose into 2 pyruvate
• NADH and 2 ATP molecules are made
• Does not require oxygen

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What happens in glycolysis step 2 of cellular
respiration?
3.6 Mitochondria and cellular metabolism

• Citric acid cycle
• A cyclical pathway that occurs in the
  mitochondria
• Produces NADH and 2 ATP
• Requires oxygen

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What happens in glycolysis step 3 of cellular
respiration?
3.6 Mitochondria and cellular metabolism

• Electron transport chain
• Series of molecules embedded in the mitochondrial
  membrane
• NADH made in steps 1 and 2 carry electrons here
• 32-34 ATP are made depending on the cell
• Requires oxygen as the final electron acceptor in
  the chain

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Oxygen is needed as the Final Electron acceptor
in the ETC

• - At the end of the chain the electrons are
  accepted by oxygen creating an anion (O-) inside,
  which has a strong affinity for the cations (H)
  outside.
• - Chemiosmosis generates ATP
• - H from the outside moves toward O-
  on the
• inside through special membrane
  channels
• that are coupled to ATP synthase
• - High-energy diffusion of H drives the
  reaction
• ADP P ? ATP.
• - H combines with O- inside the mitochondria
  creating water (H2O)

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Oxidative Phosphorylation
Occurs on a membrane, the mitochondrial cristae,
to generate most of the ATP produced from glucose
Figure 255b
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What other molecules besides glucose can be used
in cellular respiration?
3.6 Mitochondria and cellular metabolism

• Other carbohydrates
• Proteins
• Lipids
• Nucleic Acids

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Lipolysis Lipid Catabolism

• Hydrolyzes triglycerides (fat storage) ?
• 
  glycerol and three fatty acids
• Glycerol
• Glycerol ? pyruvic acids in the cytoplasm
• Pyruvic acid catabolized through TCA in
  mitochondria
• Fatty Acids
• Fatty acids are catabolized
• Enter the TCA as two-carbon fragments
• For each two-carbon fragment of fatty acid
  produced by beta-oxidation, the cell can generate
  17 molecules of ATP
• This is 1.5 times the energy production as with
  glucose
• Generates more energy but requires more oxygen
• Occurs much more slowly than equal carbohydrate
  metabolism

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Protein and Amino Acid Catabolism

• 1. Protein ? amino acids
• 2. Amino group (-NH2) is removed from amino acid
  in process called deamination
• Requires vitamin B6
• 3. Amino group is removed with conjunction with
  a hydrogen creating ammonia (NH3)
• Toxic
• 4. Liver converts the NH3 ? urea
• Harmless and excreted by the kidney
• 5. Remaining amino acid carbon chains are used
  at various stages in the Citric Acid Cycle to
  generate ATP
• Amount of ATP produced varies

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Amino Acid Catabolism
Figure 2510 (Navigator)
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Protein and Amino Acid Catabolism

• Not a Practical Source of Quick Energy
• Typically only used in starvation situations
• Harder to break apart than carbohydrates or
  lipids
• Proteins are structural and functional parts of
  every cell
• Thus tend to only be used when no other energy
  source is available
• Amino acids are simply recycled by hydrolysis of
  peptide bonds in one protein, to be reassembled
  by dehydration synthesis into the next.

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Nucleic Acid Catabolism

• DNA is never catabolized for energy
• RNA can be broken down into
• Simple sugars
• Nitrogenous bases
• Sugars
• Metabolized in glycolysis but only the pyrimidine
  bases (uracil and cytosine) can be processed in
  the TCA cycle
• Purines (adenine and guanine) are deaminated and
  excreted as uric acid making RNA metabolism very
  inefficient
• Typically nucleotides are simply recycled into
  new nucleic acid molecules and are not used for
  energy production