Chapter 5: The Working Cell

All chemical reactions involve the transfer of energy Metabolism – All chemical reactions of a cell Energy has two forms: Potential Energy – stored energy (i.e. chemical bonds) Kinetic Energy – energy of movement

Potential and Kinetic Energy (5-1)

Laws of Energy Conservation of energy – Energy cannot be created; only changed – Total energy in a closed system remains constant Entropy – Available energy is lost when changes occurs – All processes cause increases in disorder as energy is lost

Fig. 5-2

Energy is carried by molecules A.T.P. Adenosine TriPhosphate Energy molecule found in all living organisms Adenine Base with three Phosphate groups Breaking the phosphate-phosphate bond releases stored energy to be used by to the cell

ATP is rechargeable (Fig. 5-9)

ATP in action

ATP Synthase Turns ADP + P i into ATP Energy comes from H + that are pumped across a membrane then move through a channel in ATP synthase

Reactions Require Energy Activation Energy increases the kinetic energy of molecules More movement increases the likelihood of collisions. Enzymes lower the activation energy of a reaction

Enzymes are Protein Catalysts Catalysts are not used up in the reaction Each enzyme performs a specific reaction. Enzymes end in “ase” (ex: catalase)

How do enzymes work? Reactants (Substrate) bind to enzyme’s active site “Induced Fit” Hypothesis

Induced Fit (5.9)

Multiple enzymes create metabolic pathways which can produce a variety of products (NIB)

Enzyme Regulation Enzymes can be inhibited by molecules blocking the active site Allosteric regulation: secondary site regulates enzyme Enzymes can be inhibited by negative feedback

Enzyme control (5.10)

If an enzyme changes, substrates are unable to bind. The enzyme is denatured – Increased Heat – Change pH Enzymes perform within a narrow temperature and pH range.

Diffusion Molecules move randomly through a fluid because of their kinetic energy. Net movement is from areas of high concentration to areas of low concentration This high -> low movement occurs until the concentration is equal throughout (equilibrium).

Membrane proteins (5.11)

Transport Across Membranes Diffusion - movement of molecules from high concentration to low concentration. Equilibrium is reached and the concentration on both sides remain constant In cells transport can be – Simple – move straight through membrane – Facilitated – passes through channel or carrier proteins

Diffusion Through a Membrane

Osmosis Diffusion of free water across membrane Moves from low concentration of salts to high concentration – think slugs Osmosis controlled to maintain cell size and shape

Free water molecules diffuse through a membrane

Isotonic solution Salt concentration is the same inside and outside of a cell. Net movement of water is zero.

Hypertonic solution Salt concentration is higher outside the cell. Net movement of water is out of the cell.

Hypotonic solution Salt concentration is lower outside the cell. Net movement of water is into the cell.

Active Transport (5.16) Maintains high concentration. Requires energy (ATP) to move molecules.

Endocytosis Cell membrane engulfs molecules/ microorganisms Vesicles carry material where they are broken down

Exocytosis – 5.18 Vesicles release molecules

Receptor Proteins Play a Role in Cell Communication

Exam 1 50 questions - multiple choice Bring Scantron Number 2 pencil Extra credit assignments – 10 points Sample questions