Transcript Chapter 3

Chapter 3
Biology 25: Human
Biology
Prof. Gonsalves
Los Angeles City College
Loosely Based on Mader’s Human Biology,7th edition
Cell Theory: Developed in late 1800s.
1. All living organisms are made up of
one or more cells.
2. The smallest living organisms are
single cells, and cells are the functional
units of multicellular organisms.
3. All cells arise from preexisting cells.
Microscope Features
Magnification:
– Increase in apparent size of an object.
– Ratio of image size to specimen size.
Resolving power: Measures clarity of image.
– Ability to see fine detail.
– Ability to distinguish two objects as separate.
– Minimum distance between 2 points at which
they can be distinguished as separate and
distinct.
Microscopes
Light Microscopes: Earliest microscopes used.
Lenses pass visible light through a specimen.
– Magnification: Highest possible from 1000 X to
2000 X.
– Resolving power: Up to 0.2 mm (1 mm = 1/1000
mm).
Types of Microscope
Electron Microscopes: Developed in 1950s. Electron
beam passes through specimen.
– Magnification: Up to 200,000 X.
– Resolving power: Up to 0.2 nm (1nm =
1/1’000,000 mm).
Two types of electron microscopes:
1. Scanning Electron Microscope: Used to study
cell or virus surfaces.
2. Transmission Electron Microscope: Used to
study internal cell structures.
Components of All Cells:
1. Plasma membrane: Separates cell contents from
outside environment. Made up of phospholipid
bilayers and proteins.
2. Cytoplasm: Liquid, jelly-like material inside cell.
3. Ribosomes: Necessary for protein synthesis.
Prokaryotic versus Eukaryotic Cells
Feature
Prokaryotic
Eukaryotic
Organisms
Bacteria
All others (animals, plants,
fungi, and protozoa)
Nucleus
Absent
Present
DNA
One chromosome
Multiple chromosomes
Size
Small (1-10 um)
Large (10 or more um)
Membrane
Bound
Organelles
Absent
Present (mitochondria,
golgi, chloroplasts, etc.)
Division
Rapid process
(Binary fission)
Complex process
(Mitosis)
Eukaryotic Cells
–
Include protist, fungi, plant, and animal cells.
–
Nucleus: Protects and houses DNA
–
Membrane-bound Organelles: Internal structures
with specific functions.
•
•
•
•
Separate and store compounds
Store energy
Work surfaces
Maintain concentration gradients
Functions of Cell Membranes
1. Separate cell from nonliving environment. Form
most organelles and partition cell into discrete
compartments.
2. Regulate passage of materials in and out of the
cell and organelles. Membrane is selectively
permeable.
3. Receive information that permits cell to sense
and respond to environmental changes.
• Hormones
• Growth factors
• Neurotransmitters
4. Communication with other cells and the
organism as a whole. Surface proteins allow cells
to recognize each other, adhere, and exchange
materials.
I. Fluid Mosaic Model of the Membrane
1. Phospholipid bilayer: Major component
is a phospholipid bilayer.
• Hydrophobic tails face inward
• Hydrophilic heads face water
2. Mosaic of proteins: Proteins “float” in
the phospholipid bilayer.
3. Cholesterol: Maintains proper
membrane fluidity.
The outer and inner membrane surfaces
are different.
A. Fluid Quality of Plasma Membranes
– In a living cell, membrane has same fluidity as
salad oil.
• Unsaturated hydrocarbon tails INCREASE
membrane fluidity
– Phospholipids and proteins drift laterally.
• Phospholipids move very rapidly
• Proteins drift in membrane more slowly
– Cholesterol: Alters fluidity of the membrane
• Decreases fluidity at warmer temperatures (> 37oC)
• Increases fluidity at lower temperatures (< 37oC)
B. Membranes Contain Two Types of Proteins
1. Integral membrane proteins:
Inserted into the membrane.
Hydrophobic region is adjacent to hydrocarbon tails.
2. Peripheral membrane proteins:
Attached to either the inner or outer membrane surface.
Functions of Membrane Proteins:
1. Transport of materials across membrane
2. Enzymes
3. Receptors of chemical messengers
4. Identification: Cell-cell recognition
5. Attachment:
• Membrane to cytoskeleton
• Intercellular junctions
C. Membrane Carbohydrates and Cell-Cell
Recognition
– Found on outside surface of membrane.
– Important for Cell-cell recognition: Ability of one cell
to “recognize” other cells.
• Allows immune system to recognize self/non-self
• Include:
– Glycolipids: Lipids with sugars
– Glycoproteins: Proteins with sugars
– Major histocompatibility proteins (MHC or transplantation
antigens).
• Vary greatly among individuals and species.
• Organ transplants require matching of cell markers
and/or immune suppression.
The cell plasma membrane is Selectively Permeable
A. Permeability of the Lipid Bilayer
1. Non-polar (Hydrophobic) Molecules
– Dissolve into the membrane and cross with ease
– The smaller the molecule, the easier it can cross
– Examples: O2 , hydrocarbons, steroids
2. Polar (Hydrophilic) Molecules
– Small polar uncharged molecules can pass through
easily (e.g.: H2O , CO2)
– Large polar uncharged molecules pass with difficulty
(e.g.: glucose)
3. Ionic (Hydrophilic) Molecules
– Charged ions or particles cannot get through
(e.g.: ions such as Na+ , K+ , Cl- )
Transport Proteins in the membrane:
Integral membrane proteins that allow
for the transport of specific molecules
across the phospholipid bilayer of the
plasma membrane.
How do they work?
• May provide a “hydrophilic tunnel”
(channel)
• May bind to molecule and physically move it
• Are specific for the atom/molecule
transported
III. Passive transport: Diffusion of molecules
across the plasma membrane
A. Diffusion: The net movement of a
substance from an area of high
concentration to area of low
concentration.
Does not require energy.
B. Passive transport: The diffusion of
substance across a biological membrane.
• Only substances which can cross bilayer
by themselves or with the aid of a protein
• Does not require the cell’s energy
Passive Transport: Diffusion Across a
Membrane Does Not Require Energy
IV. Osmosis:
The diffusion of water across a semi-permeable
membrane.
Through osmosis water will move from an area
with higher water concentration to an area
with lower water concentration.
Solutes can’t move across the semi-permeable
membrane.
Osmotic Pressure: Ability of a solution to take up water through osmosi
Example: The cytoplasm of a cell has a certain osmotic
pressure caused by the solutes it contains.
There are three different types of solution when compared
to the interior (cytoplasm) of a cell:
1. Hypertonic solution: Higher osmotic pressure than cell due to:
Higher solute concentration than cell or
Lower water concentration than cell.
2. Hypotonic solution: Lower osmotic pressure than cell due to:
Lower solute concentration than cell or
Higher water concentration than cell.
3. Isotonic solution: Same osmotic pressure than cell.
Equal concentration of solute(s) and water than cell.
V. Cells depend on proper water balance
Animal Cells:
Do best in isotonic solutions.
Examples:
• 0.9% NaCl (Saline)
• 5% Glucose
If solution is not isotonic, cell will be affected:
– Hypertonic solution: Cell undergoes crenation.
Cell “shrivels” or shrinks.
• Example: 5% NaCl or 10% glucose
– Hypotonic solution: Cell undegoes lysis. Cell
swells and eventually bursts.
• Example: Pure water.
VI. Facilitated Diffusion:
Some substances cannot cross the membrane by
themselves due to their size or charge.
Membrane proteins facilitate the transport of solutes
down their concentration gradient.
No cell energy is required.
Transport Proteins
– Specific : Only transport very specific
molecules (binding site)
• Glucose
• Specific ions (Na+, K+, Cl- )
VII. Active Transport:
• Proteins use energy from ATP to actively “pump”
solutes across the membrane
• Solutes are moved against a concentration gradient.
• Energy is required.
Example:
The Na+-K+ ATPase pump:
Energy of ATP hydrolysis is used to
move Na+ out of the cell and K+ into
the cell
Endocytosis:
Moving materials into cell with vesicles.
Requires use of cell energy.
1. Pinocytosis (“Cell drinking”): Small droplets of liquid are taken
into the cell through tiny vesicles.
Not a specific process, all solutes in droplets are taken in.
2. Phagocytosis (“Cell eating”): Large solid particles are taken in by
cell.
Example: Amoebas take in food particles by surrounding them
with cytoplasmic extensions called pseudopods.
Particles are surrounded by a vacuole.
Vacuole later fuses with the lysosome and contents are digested.
Endocytosis Uses Vesicles to Move
Substances into the Cell
Endocytosis:
3. Receptor mediated endocytosis: Highly specific.
Materials moved into cell must bind to specific receptors
first.
Example: Low density lipoproteins (LDL):
– Main form of cholesterol in blood.
– Globule of cholesterol surrounded by single layer of
phospholipids with embedded proteins.
– Liver cell receptors bind to LDL proteins and remove
LDLs from blood through receptor mediated
endocytosis.
– Familial hypercholesterolemia: Genetic disorder in
which gene for the LDL receptor is mutated.
Disorder found in 1 in 500 human babies worldwide.
Results in unusually high levels of blood cholesterol.
Blood Cholesterol is Taken Up by Liver Cells through
Receptor Mediated Endocytosis
Exocytosis:
Used to export materials out of cell.
Materials in vesicles fuse with cell
membrane and are released to outside.
• Tear glands export salty solution.
• Pancreas uses exocytosis to secrete
insulin.
Membrane-Bound Organelles of Eukaryotic Cells
•
Nucleus
•
Rough Endoplasmic Reticulum (RER)
•
Smooth Endoplasmic Reticulum (SER)
•
Golgi Apparatus
•
Lysosomes
•
Vacuoles
•
Chloroplasts
•
Mitochondria
Nucleus
Structure
•
Double nuclear membrane (envelope)
•
Large nuclear pores
DNA (genetic material) is combined with histones and
exists in two forms:
•
–
–
•
Chromatin (Loose, threadlike DNA, most of cell life)
Chromosomes (Tightly packaged DNA. Found only
during cell division)
Nucleolus: Dense region where ribosomes are made
Functions
•
•
House and protect cell’s genetic information (DNA)
Ribosome synthesis
Structure of Cell Nucleus
Endoplasmic Reticulum (ER)
– “Network within the cell”
– Extensive maze of membranes that branches
throughout cytoplasm.
– ER is continuous with plasma membrane and outer
nucleus membrane.
– Two types of ER:
• Rough Endoplasmic Reticulum (RER)
• Smooth Endoplasmic Reticulum (SER)
Rough Endoplasmic Reticulum (RER)
– Flat, interconnected, rough membrane sacs
– “Rough”: Outer walls are covered with ribosomes.
– Ribosomes: Protein making “machines”.
May exist free in cytoplasm or attached to ER.
– RER Functions:
• Synthesis of cell and organelle membranes.
• Synthesis and modification of proteins.
• Packaging, and transport of proteins that are secreted
from the cell.
– Example: Antibodies
Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)
– Network of interconnected tubular smooth
membranes.
– “Smooth”: No ribosomes
– SER Functions:
• Synthesis of phospholipids, fatty acids, and steroids
(sex hormones).
• Breakdown of toxic compounds (drugs, alcohol,
amphetamines, sedatives, antibiotics, etc.).
• Helps develop tolerance to drugs and alcohol.
• Regulates levels of sugar released from liver into the
blood
• Calcium storage for cell and muscle contraction.
Smooth Endoplasmic Reticulum (SER)
Golgi Apparatus
– Stacks of flattened membrane sacs that may be
distended in certain regions. Sacs are not
interconnected.
– First described in 1898 by Camillo Golgi (Italy).
– Works closely with the ER to secrete proteins.
– Golgi Functions:
• Receiving side receives proteins in transport vesicles
from ER.
• Modifies proteins into final shape, sorts, and labels
proteins for proper transport.
• Shipping side packages and sends proteins to cell
membrane for export or to other parts of the cell.
• Packages digestive enzymes in lysosomes.
The Golgi Apparatus: Receiving,
Processing, and Shipping of Proteins
Lysosomes
– Small vesicles released from Golgi containing at
least 40 different digestive enzymes, which can
break down carbohydrates, proteins, lipids, and
nucleic acids.
– Optimal pH for enzymes is about 5
– Found mainly in animal cells.
– Lysosome Functions:
• Molecular garbage dump and recycler of
macromolecules (e.g.: proteins).
• Destruction of foreign material, bacteria, viruses, and
old or damaged cell components.
• Digestion of food particles taken in by cell.
• After cell dies, lysosomal membrane breaks down,
causing rapid self-destruction.
Lysosomes: Intracellular Digestion
Lysosomes, Aging, and Disease
– As we get older, our lysosomes become leaky,
releasing enzymes which cause tissue damage and
inflammation.
• Example: Cartilage damage in arthritis.
– Steroids or cortisone-like anti-inflammatory agents
stabilize lysosomal membranes, but have other
undesirable effects (affect immune function).
– Diseases from “mutant” lysosome enzymes are
usually fatal:
•
•
Pompe’s disease: Defective glycogen breakdown in liver.
Tay-Sachs disease: Defective lipid breakdown in brain.
Common genetic disorder among Jewish people.
Mitochondria (Sing. Mitochondrion)
– Site of cellular respiration:
Food (sugar) + O2 -----> CO2 + H2O + ATP
– Change chemical energy of molecules into the
useable energy of the ATP molecule.
– Oval or sausage shaped.
– Contain their own DNA, ribosomes, and make some
proteins.
– Can divide to form daughter mitochondria.
– Structure:
•
Inner and outer membranes.
•
Intermembrane space
•
Cristae (inner membrane extensions)
•
Matrix (inner liquid)
Mitochondria Harvest Chemical Energy
From Food
The Cytoskeleton
Complex network of thread-like and tube-like structures.
Functions: Movement, structure, and structural support.
Three Cytoskeleton Components:
1. Microfilaments: Smallest cytoskeleton fibers.
Important for:
•
Muscle contraction: Actin & myosin fibers in muscle
cells
•
“Amoeboid motion” of white blood cells
Components of the Cytoskeleton are
Important for Structure and Movement
Three Cytoskeleton Components:
2. Intermediate filaments: Medium sized fibers
•
•
Anchor organelles (nucleus) and hold cytoskeleton in
place.
Abundant in cells with high mechanical stress.
3. Microtubules: Largest cytoskeleton fibers. Found
in:
Centrioles: A pair of structures that help move
chromosomes during cell division (mitosis and
meiosis).
Found in animal cells, but not plant cells.
• Movement of flagella and cilia.
•
Cilia and Flagella
– Projections used for locomotion or to move
substances along cell surface.
– Enclosed by plasma membrane and contain
cytoplasm.
– Consist of 9 pairs of microtubules surrounding
two single microtubules (9 + 2 arrangement).
Flagella: Large whip-like projections.
Move in wavelike manner, used for locomotion.
• Example: Sperm cell
Cilia: Short hair-like projections.
• Example: Human respiratory system uses cilia to
remove harmful objects from bronchial tubes and
trachea.
Structure of eukaryotic Flagellum
Summary of Eukaryotic Organelles
Function: Manufacture
– Nucleus
– Ribosomes
– Rough ER
– Smooth ER
– Golgi Apparatus
Function: Breakdown
– Lysosomes
– Vacuoles
Summary of Eukaryotic Organelles
Function: Energy Processing
– Chloroplasts (Plants and algae)
– Mitochondria
Function: Support, Movement, Communication
– Cytoskeleton (Cilia, flagella, and centrioles)
– Cell walls (Plants, fungi, bacteria, and some
protists)
– Extracellular matrix (Animals)
– Cell junctions
Metabolism: All chemical processes that occur within a living
organism. Either catabolic or anabolic reactions.
I. Catabolic Reactions:
– Release energy (exergonic).
– Break down large molecules (proteins, polysaccharides)
into their building blocks (amino acids, simple sugars).
– Often coupled to the endergonic synthesis of ATP.
Examples:
1. Cellular respiration is a catabolic process:
C6H12O6 + 6 O2 -------> 6 CO2 + 6 H2O + Energy
Sugar
Oxygen
Carbon dioxide
Water
2. The digestion of sucrose is a catabolic process:
Sucrose + Water -------> Glucose + Fructose + Energy
Disaccharide
Monosaccharides
Metabolism: Catabolism + Anabolism
II. Anabolic Reactions:
– Require energy (endergonic).
– Build large molecules (proteins, polysaccharides) from
their building blocks (amino acids, simple sugars).
– Often coupled to the exergonic breakdown or hydrolysis
of ATP.
Examples:
1. Photosynthesis is an anabolic process:
6 CO2 + 6 H2O + Sunlight ----> C6H12O6 + 6 O2
Carbon
Dioxide
Water
Sugar
Oxygen
2. Synthesis of sucrose is an anabolic process:
Glucose + Fructose + Energy -------> Sucrose + H2O
Monosaccharides
Disaccharide
V. ATP: Shuttles Chemical Energy in the Cell
– Coupled Reactions:
• Endergonic and exergonic reactions are often coupled to
each other in living organisms.
• The energy released by exergonic reactions is used to fuel
endergonic reactions.
– ATP “shuttles” energy around the cell from exergonic
reactions to endergonic reactions.
• One cell makes and hydrolyzes about 10 million
ATPs/second.
• Cells contain a small supply of ATP molecules (1-5
seconds).
– ATP powers nearly all forms of cellular work:
1. Mechanical work: Muscle contraction, beating of flagella
and cilia, cell movement, movement of organelles, cell
division.
2. Transport work: Moving things in & out of cells.
A. Structure of ATP (Adenosine triphosphate)
• Adenine: Nitrogenous base.
• Ribose: Pentose sugar, same ribose of RNA.
• Three Phosphate groups: High energy bonds.
B. ATP Releases Energy When Phosphates Are
Removed:
Phosphate bonds are rich in chemical energy and
easily broken by hydrolysis:
ATP + H2O ----> ADP + Energy + Pi
ADP + H2O ----> AMP + Energy + Pi
VI. Enzymes:
• Protein molecules that catalyze the reactions of living
organisms.
• Enzymes increase the rate of a chemical reaction without
being consumed in the process.
• Name: Substrate (or activity) + ase suffix
Examples:
– Sucrase
– Lipase
– Proteinase
– Dehydrogenase (Removes H atoms)
• Enzymes are specific: Catalyze one or a few related
reactions.
• Enzymes are efficient. Can increase the rate of a reaction
10 to billions of times!!!!
VI. Enzymes:
– Enzymes increase the rate of a chemical
reaction by lowering the activation energy
required to initiate the reaction.
– Activation energy of a reaction: Energetic
barrier that reactant molecules must
overcome for reaction to proceed.
Creation of new bonds requires breaking of
old bonds.
• Both exergonic and endergonic reactions
• Transition state :“Intermediate” state of
reactants
Enzyme Mechanism of Action:
1. Binding: Enzyme binds to the reactant(s), forming an
enzyme-substrate complex.
• Substrate: The reactant the enzyme acts upon to
lower the activation energy of the reaction.
• Active site: Region on enzyme where binding to
substrate occurs.
– Active site dependent upon proper 3-D conformation.
Enzyme Mechanism of Action:
2. Induced fit model: After enzyme binds to substrate, it
changes shape and lowers activation energy of the
reaction by one of several mechanisms:
• Straining chemical bonds of the substrate
• Bringing two or more reactants close together
• Providing “micro-environment” conducive to
reaction
3. Release: Once product is made, it is released from active
site of enzyme.
Enzyme is ready to bind to another substrate molecule.
CELLULAR RESPIRATION BANKS ATP
REACTION:
C6H12O6 +
(Glucose)
6O2 ----> 6CO2 + 6H2O + ENERGY
(Oxygen)
(Carbon dioxide) (Water)
What happens to the energy in glucose or other
food molecules?
– Only about 40% of energy is turned into
ATP
– The rest is lost as metabolic heat.
– One ATP molecule has about 1% of the
chemical energy found in glucose.
MAJOR CATABOLIC PATHWAYS
A. Aerobic (Cellular) respiration:
– Requires oxygen.
– Most commonly used catabolic pathway.
– Over 30 reactions. Used to extract energy
from glucose molecules.
– Final electron acceptor: Oxygen.
– Most efficient: 40% of glucose energy is
converted into ATP.
REACTION:
C6H12O6 +
Glucose
6O2
Oxygen
---> 6CO2 + 6H2O + ENERGY
Carbon dioxide Water
V. Three Stages of Cellular Respiration
A. Glycolysis
B. Kreb’s Cycle
C. Electron Transport Chain & Chemiosmosis
A. Glycolysis: “Splitting sugar”
–
–
–
–
Occurs in the cytoplasm of the cell
Does not require oxygen
9 chemical reactions
Net result: Glucose molecule (6 carbons each) is split
into two pyruvic acid molecules of 3 carbons each.
– Yield per glucose molecule:
2 ATP ( Substrate-level phosphorylation)
2 NADH + 2 H+
(2 ATP are “invested” to get 4 ATP back)
– Pyruvic acid diffuses into mitochondrial matrix
where all subsequent reactions take place.
Conversion of Pyruvate to Acetyl CoA
– Before entering the next stage, pyruvic acid
(3C) must be converted to Acetyl CoA (2 C).
– A carbon atom is lost as CO2.
– Yield per glucose molecule: 2 NADH + 2 H+
B. Kreb’s Cycle
– Occurs in the matrix of the mitochondrion
– A cycle of 8 reactions
• Reaction 1: Acetyl CoA (2C) joins with 4C
molecule (oxaloacetic acid) to produce citric acid
(6C).
• Reactions 2 & 3: Citric acid loses 2C atoms as
CO2.
• Reactions 4 & 5: REDOX reactions produce
NADH and FADH2.
• Reactions 6-8: Oxaloacetic acid is regenerated.
B. Kreb’s Cycle
– Carbons are released as CO2
– Yield per glucose molecule:
2 ATP (substrate-level phosphorylation)
6 NADH + 6 H+
2 FADH2
C. Electron Transport Chain & Chemiosmosis
– Most ATP is produced at this stage
– Occurs on inner mitochondrial membrane
– Electrons from NADH and FADH2 are transferred
to electron acceptors, which produces a proton
gradient
– Proton gradient used to drive synthesis of ATP.
– Chemiosmosis: ATP synthase allows H+ to flow
across inner mitochondrial membrane down
concentration gradient, which produces ATP.
– Ultimate acceptor of H+ and electrons is OXYGEN,
producing water.
C. Electron Transport Chain & Chemiosmosis
Yield of ATP through Chemiosmosis:
– Each NADH produces 3 ATP
– Each FAHD2 produces 2 ATP
2 NADH (Glycolysis) x 3 ATP
2 NADH (Acetyl CoA) x 3 ATP
= 6 ATP
= 6 ATP
6 NADH (Kreb’s cycle) x 3 ATP
= 18 ATP
2 FADH2 (Kreb’s cycle) x 2 ATP
= 4 ATP
________________
32 - 34 ATP
These ATPs are made by oxidative phosphorylation
or chemiosmosis.
VIII. Total Energy from cellular respiration
Process
Substrate
Oxidative
Phosphoryl e-Carrier Phosphoryl TOTAL
Glycolysis 2 ATP
Acetyl CoA
Formation
Kreb’s
2 ATP
2 NADH ---> 4 - 6 ATP
6-8 ATP
2 NADH ---> 6 ATP
6 ATP
6 NADH ---> 18 ATP
2 FADH2 ---> 6 ATP
Total yield per glucose :
24 ATP
__________
36-38 ATP
THREE MAJOR CATABOLIC
PATHWAYS
B. Anaerobic respiration:
– Does not require oxygen.
– Used by bacteria that live in
environments without oxygen.
– Final electron acceptor: Inorganic
molecule.
– Very inefficient: Only 2% of glucose
energy is converted into ATP.
– Final products: Carbon dioxide, water,
and other inorganic compounds.
THREE MAJOR CATABOLIC PATHWAYS
C. Fermentation:
– Does not require oxygen.
– Used by yeast, bacteria, and other cells when
oxygen is not available.
– Final electron acceptor: Organic molecule.
– Very inefficient: Only 2% of glucose energy is
converted into ATP.
– Products depend on type of fermentation:
• Lactic acid fermentation: Used to make cheese and
yogurt. Carried out by muscle cells if oxygen is low.
• Alcoholic fermentation: Used to make alcoholic
beverages. Produces alcohol and carbon dioxide.