Post on 12-Jan-2016
How Cells Work
Chapter 4
Beer, Enzymes and Your Liver
• Alcohol is toxic
• Cells in liver break down alcohol to nontoxic compounds
• Breakdown is accelerated by enzymes
• Heavy drinking damages liver and other organs
Impacts, Issues Video
Alcohol, Enzymes, and Your LiverAlcohol, Enzymes, and Your Liver
Energy Laws
• Energy: the capacity to do work
• Total amount of energy in the universe is constant
• Energy flows from higher to lower energy forms
ENERGY LOSTWith each conversion, there is a one-way flow of a bit of energy back to the environment.
ENERGY GAINEDSunlight energy reaches environments on Earth. Producers secure some and convert it to stored forms of energy. They and all other organisms convert stored energy to forms that can drive cellular work.
ENERGY LOSTEnergy continually flows from the sun.
Fig. 4-1, p.59
ATP
3 phosphate groups
nucleotide base (adenine)
sugar (ribose)
• Main energy carrier in cells
• Can give up phosphate group to another molecule
• Phosphorylation energizes molecules to react
The Cell’s Energy Currency
• ATP couples energy inputs and outputs
• ATP/ADP cycle regenerates ATP
Energy Input(from nutrientslike glucose) ADP + Pi
ATP
Energy Output (to allow muscle contraction)
reactions that
release energy
reactions that
require energy
cellular work
(e.g., synthesis,breakdown, or rearrangement of substances;contraction of muscle cells; active transport across a cell membrane)
ATP
ADP + Pi
ATP
Fig. 4-2, p.59
base
sugar
three phosphategroups
Structure of ATP
The Role of ATP
Energy Changes
• Endergonic reactions require energy– Synthesis of glucose from carbon dioxide
and water during photosynthesis
• Exergonic reactions release energy– Breakdown of glucose to carbon dioxide
and water by aerobic respiration
glucose (product)
energyin
starting substances
+ 6
+ 6O2
6
Fig. 4-3a, p.60
Energy in Glucose
Photosynthesis
energy out
products
glucose + 6O2
(starting substances)
Fig. 4-3b, p.60
+ 66
Energy in Glucose
This energy helps make ATP
Metabolic Pathways
• Biosynthetic (anabolic) pathways– Require energy inputs– Assemble large molecules from subunits– Photosynthesis
• Degradative (catabolic) pathways– Release energy– Breakdown large molecules to subunits– Aerobic respiration
Enzymes
• Catalyze (speed up) reactions
• Are proteins
Factors Influencing Enzyme Activity
Coenzymes and cofactors
Allosteric regulators
Temperature
pH
Salt concentration
Effect of Temperature
• Small increase in temperature increases molecular collisions, reaction rates
• High temperatures disrupt bonds and destroy the shape of active site
Enzymes and temperatureEnzymes and temperature
Effect of TemperatureEffect of Temperature
Concentration Gradient
• Different numbers of molecules or ions in different regions
• Substances tend to move down gradient - from higher to lower concentration
oxygen, carbon dioxide, and other small, nonpolar molecules; some water molecules
glucose and other large, polar, water-soluble molecules; ions (e.g.,H+, Na+, K+, Ca++, Cl–)
Selective Permeability
Cell Membranes Show Selective Permeability
Selective permeability
Fig. 4-12, p.65
dye
dye
water
Diffusion
• Net movement of molecules or ions down a concentration gradient
DiffusionDiffusion
Diffusion of dye in water
Factors Affecting Diffusion Rate
• Steepness of concentration gradient– Steeper gradient, faster diffusion
• Molecular size– Smaller molecules, faster diffusion
• Temperature– Higher temperature, faster diffusion
• Electrical or pressure gradients
Passive and Active Transport
• Doesn’t require energy inputs
• Solutes diffuse through a channel inside the protein’s interior
• Net movement is down concentration gradient
Passive Transport Active Transport• Requires ATP
• Protein is an ATPase pump
• Pumps solute against its concentration gradient
Which Way Will Water Move?
• Water diffuses across cell membranes
Osmosis
• Diffusion of water molecules across a
selectively permeable membrane,
down the water concentration gradient
• Higher solute concentration = lower
water concentration
water molecules protein molecules
semipermeable membranebetween two compartments
Fig. 4-15, p.68
Osmosis
Solute concentration and osmosis
Membrane Traffic
• Exocytosis– Vesicle fuses with membrane, releasing
substance into intracellular fluid
Membrane Traffic
• Endocytosis– Membrane forms vesicle, bringing
substance into cell
Endocytosis (vesicles in) Exocytosis (vesicles out)
Fig. 4-20, p.71
Phagocytosis
Phagocytosis
Fig. 4-18, p.70
a
b
exocytosis(out from cytoplasm)
endocytosis(into cytoplasm)