Transcript Power Point Ch. 5 Working Cell - Northern Highlands Regional HS

Honors Biology - Chapter 5
The Working Cell
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5.2 Energy Transformations in a Cell
Cell metabolism - uses or makes energy
a) exergonic reaction - make energy:
- release energy stored in molecules
- oxidation (catabolic) ex. cell respiration
b) endergonic reaction - use energy:
- use energy (ATP) to do cell work
- reduction, (anabolic)
ex. move, synthesize
Coupled reactions - energy released in exergonic
reactions is used to power endergonic
2
Chemical Reactions either store
or release energy
3
5.5 ATP - energy molecule in a cell
ATP - adenosine triphosphate
-adenine, ribose (adenosine) + three phosphates
-bonds between phosphates are easily broken
phosphate group transfers energy
4
ATP - ADP
ATP
triphosphate
ADP
+
diphosphate
P
phosphate group
P is free energy - powers cellular work
Phosphorylate - add a phosphate group to a molecule
- transfers energy to new molecule
5
ATP is renewable energy
• ATP breakdown products (ADP + P) remain in cell
• are used again to regenerate more ATP when needed
Energy from
exergonic
reactions
ATP made
in cell
respiration
Energy for
endergonic
reactions
ATP used
for cellular
work
Very fast!! 10 million ATP/second in a cell; needs help of enzymes
6
5.4 How ATP powers cellular work
Membrane Transport
• P  membrane
protein
Biosynthesis
- P  reactant
• Protein changes
shape
- Reactants bond
•Protein pushes
solute through
membrane
- Product forms
- P released
• P released
Mechanical Motion
• P onto motor protein  protein changes shape
• Pulls on muscle fibers  muscle contracts
• P released
7
Enzymes speed up reactions
5.6 Enzymes are biologic catalysts
catalyst - speeds reaction but is not
changed or used up
Substrate molecule the enzyme
acts upon
specific - only one
kind of molecule
Enzyme names
- for process or for
substrate
- end in -ase
Enzyme must fit the substrate
Active site – region on enzyme molecule that binds to
substrate molecule
Active site
substrate
Enzyme control all types of reactions
catabolic – breaking
synthesis – building
Models of Enzyme Fit
Lock-and-key model –
perfect fit, no shape
change
Induced fit – shape of
enzyme changes when
substrate attaches
12
5.7 Factors Affecting Enzyme Action
Enzymes are protein - shape is critical to function
Temperature - heat makes molecules move faster
 more contact - enzyme with substrate
 faster reaction rate
BUT - HIGH TEMPS
DENATURE
PROTEINS!
Enzymes and pH
Ions - break weak bonds holding molecule shape
• electrolyte (salts) or pH change
Enzyme activity and concentration
Increase concentration of enzyme or of substrate
- increases reaction rate BUT ONLY TO A POINT
•limiting reagent – all molecules being used
• Rate does not increase any farther
Enzyme Inhibition
1. Competitive inhibitor - another molecule competes for
active site - blocks substrate
2. Noncompetitive inhibitor – another molecule binds
somewhere else on the enzyme -> enzyme changes shape
- active site no longer fits substrate
Feedback inhibition
A molecule made in reaction
sequence inhibits the enzyme
17
Feedback
18
Feedback inhibition in enzymes
Product from later reaction
inhibits an earlier reaction
 Sequence stops
Feedback inhibition - examples
Many poisons and drugs act this way
•Penicillin (blocks bacterial wall assembly)
•Aspirin (blocks pain sensation)
•Sarin, malathion (block nerve impulses)
In ALD – Lorenzo’s Oil blocks synthesis of
long chain fatty acids
When substrate is at saturation:
Non-competitive--- active site is still open, so some
substrate molecules can still bind to active site
 reaction continues but at slower rate
21
Inhibition can be reversed
• If enough substrate molecules are present,
some will displace inhibitor molecules
22
Coenzymes
Many enzymes need the help of COFACTORS
- inorganic, ex. ions
or COENZYMES
- organic, ex. vitamins
23
5.10: Membranes organize chemical
activities in a cell
a) keep structural order
b) compartments have specific enzymes
Plasma membrane
- boundary between cell and its environment
24
Fluid Mosaic Model
Describes structure of cell membranes
• “mosaic” – sea of lipids with scattered proteins
• “fluid” – molecules float and move around
within the layer
Fluid-Mosaic Model
26
5.11 Phospholipids make cell membranes
Phospholipid = lipid molecule with phosphate
glycerol + two fatty acids + phosphate group
• phosphate group = polar end
(hydrophilic “head”)
• Fatty acids = nonpolar end
(hydrophobic “tails”)
Phospholipids form a double layer in water
Polar heads are on the outside ( touch water)
Nonpolar tails are on the inside (away from water)
- Unsaturated – keep membrane flexible
Features of the Cell Membrane
Semipermeable = some substances can pass through
- some cannot
- depends on: molecule size, charge, polar or
nonpolar, needs of cell, signals from environment
Cholesterol – scattered among the phospholipids
- in animal cells only
- keep membrane flexible in changing temperatures
Carbohydrates – glucose chains on outside of cell
- Identification “tags”
- Receptor sites for messenger molecules
Membrane Proteins
have many functions
Transport
Enzyme
Allows a specific
molecule to
pass through
the membrane
Catalyzes a
reaction inside
the cell
Receptor
Site for
messenger
molecule to
attach
Transport Proteins
• Channels, pores, and carriers
move particles across the
membrane
• Specific
• May use energy
31
Signal Transduction
Message from outside cell is relayed to a specific
molecule inside cell
Chemical signal binds to receptor protein
- message sent inside cell
- 2nd messenger relay
- causes response in cell
Ex. hormones, neurotransmitters
32
Receptor Proteins – Insulin Receptors
Receptors on cell membrane
• Insulin attaches
• Signal transduction
• Message allows glucose into cell
• Transport protein for glucose
33
Example: insulin receptors
- cause a different membrane protein to allow glucose to enter cell
34
Membrane proteins (2)
Junctions
Structure
Identification
Attach to extracellular
“SELF” – cell belongs Cells join to
form tissues, matrix or cytoskeleton;
in this organism,
Keeps internal parts
communicate organized
Ex. immunity
How do membranes keep
homeostasis?
Cell membranes are selectively permeable
•The lipid layer blocks most substances
•Some molecules can cross the membrane
– By passive or active transport
•Some are too big to cross at all
PASSIVE TRANSPORT
USES NO CELL ENERGY
Diffusion: Molecules move randomly – spread
out until evenly distributed
DIFFUSION
Diffusion: movement of particles from an
area of higher concentration to an area of
lower concentration
•Adjacent areas with different concentrations =
concentration gradient
•Particles move in all directions (random)
•NET movement is from high concentration to low
•“Down the concentration gradient”
Diffusion
• Particles spread out until evenly distributed
 equilibrium (homogeneous)
• Still move randomly, but
 NO further change in concentration
Cell Membranes
allow some particles to cross
Particles can diffuse across
the lipid bilayer if they are:
• Small
• Nonpolar (lipid-soluble)
Examples: CO2 , O2, fatty acids
Two or more solutes – each moves down its own gradient
Ex. Gas exchange in lungs
41
Others need help to get through
- Facilitated Diffusion
Transport proteins- specific for one substance
.
Down the gradient - no cell energy needed
Particles can cross by facilitated diffusion if
they are:
• Small
• POLAR (water soluble) or CHARGED
Examples: H2O, glucose, amino acids, ions
42
Facilitated Diffusion
• Diffusion through a membrane protein
43
5.15: Facilitated Diffusion
Channel (pore)
Carrier
44
Why do particles cross the
membrane?
Depends on:
• Size
• Polar or nonpolar
• Charge
• Concentration gradient
• Chemical signals inside or outside cell
• Needs of the cell
45
5.16: OSMOSIS
Diffusion of water across a membrane
Important process in cell homeostasis
Water crosses the cell membrane easily
- Small enough to pass between lipid molecules
- Also pass through special proteins, aquaporins
Water diffuses easily across
membranes; many solutes don’t
47
Osmotic Pressure – tendency of water
to move across a membrane
Which way does water go?
- down its gradient
From side with more water (less solutes)
to side with less water (more solutes)
Type of solutes doesn’t matter, only total concentration
48
Osmotic equilibrium
when concentrations are equal
or when force of gravity equals osmotic pressure
49
Why osmosis matters
• Water crosses membrane easily, faster than
many solutes
• Water will try to reach equilibrium
• If NET water moves into or out of cell 
disrupts homeostasis
• Water balance is needed for homeostasis
TONICITY = osmotic pressure in cells
ISOTONIC
Equal concentrations of solutes inside and outside cell
–Equal concentrations of water
–Water goes in and out of cell at equal rates
Isotonic pressure in cells
• No NET movement of
water into or out of cell
• Normal water pressure
in animal cells
• Wilted (“flaccid”) water
pressure in plant cells
When solute concentration is different on two
sides of a membrane
lower solute concentration = hypotonic
Higher solute concentration = hypertonic
Solutes will move down their gradient IF THEY
CAN CROSS THE MEMBRANE
Water concentration is OPPOSITE of solutes
Low solutes  HIGH WATER concentration
High solutes  LOW WATER concentration
Water WILL diffuse down its gradient and
crosses the cell membrane easily
Goes TO whichever side has more solutes
Cells in hypertonic solutions
Solutes are higher outside cell, water is lower
Water leaves cell by osmosis
Cytoplasm shrinks - “plasmolysis”
- animal cells: shrivel
- plant cells: low turgor pressure
- cytoplasm pulls away from cell wall
- but cell wall does not shrink
Cells in hypotonic solutions
Solutes are lower outside cell, water is higher
Water enters cell by osmosis
Cytoplasm swells
- animal cells: swell, may burst (“lyse”)
- plant cells: high osmotic pressure “turgor”
- won’t burst (have a cell wall)
- “Turgid” – stiff and firm, upright stem
Isotonic
Hypotonic
Hypertonic
57
Osmosis in Animal Cells
Animal cells like ISOTONIC conditions best
Osmosis in Plant Cells
Plant cells like HYPOTONIC conditions best
Red blood cells - in isotonic in hypotonic in hypertonic
Plant cells in
hypotonic solution
Plant cells in
hypertonic solution
60
Contractile Vacuoles
Fresh-water protists (like Paramecia or
Amoeba) must constantly remove water that
comes into the cell by osmosis
5.18 Active transport uses cell energy
Protein pumps move particles against the gradient
- from LOW concentration to HIGH
Cells can maintain a concentration
that is NOT at equilibrium
62
Why would cells use active
transport?
1) To concentrate substances:
Examples: kidneys : wastes in urine
- intestine : nutrients in blood
2) To maintain an ion concentration
- sodium-potassium pump for nerve impulses
64
Na+ - K+
pump
65
Proton (H+) pump
in photosynthesis and cell respiration
66
Bulk Transport – uses energy
For particles too big to pass through membrane
Endocytosis = brings material into cell
- fold cell membrane around it form a vacuole
a. Phagocytosis = “cell eating”
- large particles or whole cells
- examples: amoeba
white blood cells
pseudopods
Endocytosis
– substance pulled INTO CELL
68
Pinocytosis – “cell drinking”
Small folds of membrane take in liquids
Example: small intestine absorbs
some water this way
5.19: Exocytosis – substance goes OUT OF cell
- enclosed in membrane vesicle
- vesicle fuses with plasma membrane
- releases contents outside cell
70
Exocytosis
• For secretory cells
• ex. Hormones from endocrine glands:
pancreas - insulin  bloodstream
• digestive juices from pancreas, intestine 
food cavity
71
Receptor-mediated endocytosis
Receptors on plasma membrane for a specific
molecule
Membrane encloses molecule  forms a vesicle
“coated pit” on
membrane
72
LDL Cholesterol
cholesterol: essential for normal cell functioning and
for making other lipids
a) carried in the blood by low-density lipoproteins (LDL)
b) LDL has a surface protein that fits a receptor on cell
membranes
- cells remove it from the blood by receptor-mediated
endocytosis
73
5.20: Hypercholesterolemia
If receptors are faulty or missing, cholesterol remains in
the blood  collects inside blood vessels (high risk
for heart disease) and in pockets under the skin
Cholesterol in pockets under skin
cholesterol inside blood vessel
74