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ATP: The energy currency of the cell The ATP Cycle:

Changing the rate of catabolic and anabolic reactions- How do

you control these chemical reactions?

Enzymes as biological catalysts– Activation Energy - the probability of a

reaction• Enzymes effect the rate of reactions by changing the

amount of activation energy needed for the reaction

Enzymes and Activation Energy

Enzymes and Activation Energy A cartoon view of sucrase activity:breaking down sucrose

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Other factors that influence enzyme activity:

• Cofactors: metal ions and coenzymes– Vitamins like niacin and

riboflavin• Temperature, pH• Metabolic Pathways

– Regulation and Organization

– Negative feedback

Temperature and pH Optima

Enzyme regulation Metabolism

• The sum total of all the chemical reactions happening in a cell (or living thing)

• Two main types of chemical reactions– Anabolic: unfavorable; uses energy to do work,

transport, synthesize, move…– Catabolic: favorable; breakdown of molecules

release energy used to fuel other reactions

Anabolic and Catabolic Reactions Intro to Cell Structure

• Cell Theory: – All organisms are made of one or more cells– Cells are the smallest living thing– Cells come from other cells (today)

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Two Main Classes of Cells

• Prokaryotic (Bacteria and Archaea)– Pro = “Before”; Karyon = “Kernel”– No nucleus, DNA coiled up inside cell

• Eukaryotic (Everything else)– Eu = “True”– DNA inside membrane bound organelle inside

cell, the nucleus

3 Domains of Life

Eukaryotic Cell (non bacterial)Prokaryotic Cell (bacteria)

Size Differences

Prokaryotic Cell Animal Cell

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Plant Cell Why are cells so small? i.e. What are the determinants of cell size?

1- Surface area to volume ratio

2- Diffusion rates

Surface Area to Volume Ratios

Diffusion of oxygen in Diffusion of oxygen in solutionsolution

1 1 µµm in .5 m in .5 msecmsec10 10 µµm in 50 m in 50 msecmsec100100µµm in 5 secm in 5 sec1000 1000 µµm (1mm) in 8.3 minm (1mm) in 8.3 min10000 10000 µµm (1cm) in 14 h!m (1cm) in 14 h!

Mechanisms of Cellular Transport

• Molecular Mechanisms- Solutes and Solvents– Passive Diffusion and Osmosis– Active Transport– Osmoregulation– Hypo-, Iso-, and Hypertonic

• Below, Equal, and Above

• Bulk transport: Endo- and Exocytosis

Diffusion

Hypertonic Hypotonic Isotonic

Diffusion goes in all directions…along the Concentration Gradient

Passive Transport- important to all cells… O2 and CO2

What about molecules that can’t get through the Plasma Membrane?

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Transport Proteins-Facilitated Diffusion

Still doesn’t use any energy!

Just High conc. to low

Examples:

Sugar, A.a., ions, even water!?

Osmosis- passive transport of water across a membrane

Why? Osmosis and living cells

SaltwaterFish

FreshwaterFish

Transport

• Passive- (downhill) Free or gated (chemical or ion)

• Facilitated- (downhill with a “push”)• Active-ATP mediated (uphill)

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Active Transport1. Solute attaches to binding site of transport protein

2. ATP causes the protein to change shape 3. so that solute is taken outside membrane

4. Phosphate groups leaves and causes the reverse change.

Active TransportSodium-Potassium Pumps

– Na-K pumps…up to 40% of all our energy is used for this pumping

Active Transport of Large Molecules, etc.

- Exocytosismoving things outside cell.

CryingInsulinothers

Active Transport of Large Molecules, etc.

- Endocytosismoving things inside cell- 3 ways

Endocytosis

Phagocytosis- “cell eating”

Pinocytosis- “cell drinking”

Receptor-mediated- highly specific

Review: passive and active transport compared

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What Controls all this Transport in Living Cells???

The Plasma Membrane

General functions of the Plasma Membrane

• Selective permeability to maintain separation• Control exchange of wastes and metabolites• Framework for organization of enzymes• Anchorage between cells• Binding site for hormones• Receptors for selective uptake • Intercellular identification

Membrane Structure: The Fluid Mosaic Membrane Model

• Lipid bilayer (double layer)• Nonpolar tails point inward, polar outside• Layers are “fluid”• Many things embedded within membrane

– Phospohlipids and cholesterol– Carbohydrates– Proteins

• Much of the structure and functions of the PM depend on these embedded proteins

The Singer Nicholson Fluid Mosaic Model of Membrane Structure: General Properties

• Phospholipid bilayer: 50%– Backbone of most membranes– Lateral movement only– Oily core forms hydrophobic

barrier• Proteins: 50%

– Integral and peripheral– cytosolic and exoplasmic faces

The fluidity of membranes

• Free movements of:– lipids – proteins

• Healing properties• The variable nature

of the fluidity of membranes:– Sat. vs Unsat. FA’s– Cholesterol

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Some functions of membrane proteins