• Energy– The capacity to do work

• What is work? Potential Energy

Stored energy, eg. in chemical bonds Kinetic Energy

Energy of motion

• What is the Law of Conservation of Energy?

Chapter 5 – The Working Cell

• The chemical energy of organic molecules is released in cellular respiration to make ATP in the mitochondria

ATP and Cellular Work

– Consists of adenosine plus a tail of three phosphate groups

– Is broken down to ADP, accompanied by the release of energy

Energy

Adenosine Adenosine

Phosphate transferred to othermolecules

• ATP functions in what is called energy coupling, or the ATP cycle

Cellular respiration:chemical energyharvested fromfuel molecules

Energy forcellular work

• Most enzymes are proteins with diverse structure.

• Enzymes are chemical catalysts that:– Increase the rate of a reaction. – Are not permanently altered or used up by the

reaction.– Do not change the nature of the reaction.

enzyme animation..

– Reduce the required amount of activation energy required to initiate the reaction.

• Many enzymes work by orienting molecules so that they can better contact each other.

• Each type of enzyme has has a highly-ordered, characteristic 3-dimensional shape (conformation).

• Ridges, grooves, and pockets lined with specific amino acids.

• Pockets active in catalyzing a reaction are called the active sites of the enzyme..

Activation energybarrier

Reactants

(a) Without enzyme

Products

En

zym

e

(b) With enzyme

• The molecule affected by the enzyme is the substrate.

• Substrates have specific shapes to fit into the active sites (lock-and-key model):

• Better fit may be induced (induced-fit model):

• Enzyme undergoes structural change when substrate binds..

• Enzyme names end with suffix “-ase.”– Enzymes may be named according to their

mode of action, e.g. kinase.• May specify both the substrate of the enzyme and

job category.

– Enzymes may be named for the substrate, e.g. lipase, maltase.

• Different organs may make different enzymes (isoenzymes) that have the same activity.– Differences in structure do not affect the active

sites..

• Enzyme activity can be affected by several factors:– Changes in pH and/or temperature may

denature the enzyme. These changes may break the H bonds stabilizing the molecule.

– Small molecules or ions called cofactors alter the shape of the active site and/or is needed for the substrate to bind with the active site, e.g. Ca++.

– Certain organic molecules called coenzymes are needed to transport small molecules or ions (especially H+) from one enzyme to another, e.g. NAD..

– Metabolic pathways are frequently regulated by inhibition. End-product inhibition occurs when one product binds with the enzyme and prevents it from binding with the substrate. The product may bind with the enzyme at the allosteric site. This is negative feedback.

inhibition animation..

Active siteSubstrate

Inhibitor

Enzyme

(c) Enzyme inhibition by a molecule that causes the active site to change shape

• Competitive inhibition occurs when some other imposter molecule (similar to the substrate) binds with the enzyme. This prevents the substrate from participating in any metabolic pathway. This is typically how poisons work..

SubstrateActive site

Enzyme

(a) Normal enzyme action

Inhibitor Substrate

Active site

Enzyme

(b) Enzyme inhibition by a substrate imposter

• Working cells must control the flow of materials– This is the primary function of the plasma membrane– Transport proteins also help with this task

• Transport process may be categorized by the energy requirements:– Passive transport:

• Net movement down a concentration gradient.– Does not require metabolic energy (ATP).

– Active transport:• Net movement against a concentration gradient.

– Requires ATP..

Membrane Transport

Molecules of dye Membrane

(a) Passive transport of one type of molecule

Equilibrium

(b) Passive transport of two types of molecules

Equilibrium

• Molecules/ions are in constant state of random motion due to their thermal energy.

• Diffusion is the movement of particles from an area of high concentration to and area of low concentration. Net diffusion indicates the final concentration changes.

Diffusion Animation

• Diffusion of some substances through the plasma membrane requires carriers or channels (discussed later)..

Diffusion

• Osmosis is the special term for the net diffusion of H20 across a selectively permeable membrane.

• Osmosis is the movement of H20 from a high [H20] to lower [H20] until equilibrium is reached.

• Two requirements for osmosis:– Must be difference in [solute] on the 2 sides of the

membrane.– Membrane must be impermeable to the solute.

Osmosis Animation..

Hypotonicsolution

Hypertonicsolution

Isotonic solutions

Sugar molecule(solute)

Selectively permeablemembrane

Osmosis(net movement of water)

•Hypertonic solution = has a higher concentration of solute•Hypotonic solution = has a lower concentration of solute•Isotonic solution = has an equal concentration of solute

• The survival of a cell depends on its ability to balance water uptake and loss = Osmoregulation

Water Balance in Cells

Animalcell

Normal Lysing

Shriveled

Plantcell

Flaccid (wilts) Turgid

Plasmamembrane

(a) Isotonic (b) Hypotonic (c) Hypertonic..

Shriveled

Carrier-Mediated Transport

• Molecules that are too large and/or polar to pass through the plasma membrane require protein carriers.– Facilitated diffusion is passive transport utilizing

carriers. Molecules move from high concentration to low concentration.

e.g. GLUT carriers transport glucose into human cells..

– Active transport required the expenditure of ATP. Molecules are moved from low concentration to high concentration.• The most common primary active

transport mechanism is the Na+/K+ pump. In this case, the protein carrier is an ATPase that converts ATP to ADP + Pi. The carrier transports 3 Na+ out of the cell and takes in 2 K+.

Na/K Pump Animation..

Bulk Transport• Movement of many large molecules, that cannot be

transported by carriers, at the same time.• Exocytosis:

– Fusion of the membrane-bound vesicles that contains cellular products with the plasma membrane.

Outside cell

Plasmamembrane

Cytoplasm

(a) Exocytosis

•Endocytosis:–Exocytosis in reverse.–Specific molecules can be taken into the cell because of the interaction of the molecule and protein receptor (receptor-mediated endocytosis).

Endo/Exocytosis Animation

(b) Endocytosis

Food being ingested

Pseudopodof amoeba

•Phagocytosis

•Pinocytosis