What is energy? Energy: capacity to do work – Potential energy (Example: chemical bonds) –...

What is energy?

• Energy: capacity to do work– Potential energy

(Example: chemical bonds)

– Kinetic energy (Energy of motion)

Two Laws of Thermodynamics

1. Energy cannot be created or destroyed– It can be converted from

one form to another and transferred between objects or systems

2. Entropy tends to increase– Energy tends to disperse

spontaneously – Some energy disperses at

each energy transfer, usually in the form of heat

Energy In, Energy Out• Chemical reactions

– Reactants (molecules in)

– Products (molecules out)

• Endergonic reactions (energy-requiring)– Photosynthesis

• Exergonic reactions (energy-releasing)– Aerobic respiration

Energy Flows in One Direction

• Energy is not cycled – In from the sun; into and

out of ecosystems• All living things harvest

external energy– Producers and consumers

use energy to assemble, rearrange, and dispose of substances

• Substances cycle among organisms over time

What is ATP?• Adenosine

triphosphate (ATP) – Main energy carrier

between cell reaction sites

– Currency of the cell• Phosphorylation

– Phosphate-groups transfer to and from ATP

– Couple metabolic reactions that release usable energy to metabolic reactions

What enzymes do?• Enzymes are

catalysts – Speed reaction rates

by lowering activation energy

– Proteins in nature• Activation energy

– Minimum energy needed to start a reaction

• Each enzyme functions best within a characteristic range of temperature, salt concentration, and pH

How enzymes work?• Active site

– Small cleft in enzyme’s surface where reactions occur

• How enzymes lower activation energy – concentrating substrate molecules – orienting substrates to favor reaction – inducing fit between substrate and active

site– excluding water from active site

• Activation energy allows enzyme to react with substrate.

What are cofactors?• Most enzymes

require assistance of cofactors– Inorganic metal ions– Organic coenzymes

(vitamins)• Example: Catalase

(Antioxidant)– Cofactor: Iron

Metabolic pathways• Cells concentrate, convert,

and dispose of most substances in orderly, enzyme-mediated reaction sequences

• Biosynthetic pathways – Construct large molecules

from smaller ones– Require energy

• Photosynthesis– Main biosynthetic pathway

in the biosphere– Autotrophs

Degradative pathways• Degradative

pathways – Break down

molecules to smaller products

– Release usable energy

• Aerobic respiration – Main degradative

pathway in the biosphere

– Heterotrophs• Oxidation–reduction

(redox) reactions – Electron transfers

used in metabolic pathways

How substances cross membranes?• Diffusion

– process by which molecules intermingle as a result of their energy of motion

• Passive– facilitated diffusion, solute moves down

its concentration gradient and no energy input is required.

• Active Transport– Active transport uses energy to move a solute "uphill" against its gradient,

What is diffusion?• Diffusion

– Net movement of molecules to a region where they are less concentrated • Number of atoms or

molecules in a given volume

• Diffusion rates are influenced by:– Temperature – Molecular size– Gradients of pressure,

charge, and concentration

– Selective Permeability

What is facilitated diffusion?

• Many solutes cross membranes through transport proteins (open or gated channels)

• Facilitated diffusion (passive transport) does not require energy input– Solute diffuses down its

concentration gradient through a transporter

– Example: Glucose transporters

What is active transport?• Active transporters require

ATP energy to move a solute against its concentration gradient – Maintain gradients across cell

membranes– Example: Calcium pumps

What are endocytosis and exocytosis?

• Exocytosis– Cytoplasmic vesicle

fuses with plasma membrane

– Contents are released outside

• Endocytosis– Part of plasma

membrane forms a vesicle that sinks into the cytoplasm

Three types of endocytosis• Receptor-mediated

endocytosis– Substance binds to

surface receptors– Pit forms endocytotic

vesicle• Phagocytosis (“cell

eating”)– Amoebas use

pseudopods to engulf prey

• Bulk-phase endocytosis– Vesicle forms around

extracellular fluid

Which way will water move?

• Osmosis – The diffusion of

water across a selectively permeable membrane

– Water molecules follow their concentration gradient, influenced by solute concentration

What is tonicity?• Relative

concentrations of two solutes separated by a semipermeable membrane– Hypertonic fluid

(higher solute concentration)

– Hypotonic fluid (lower solute concentration)

– Isotonic solutions (two solutions with the same tonicity)