Bio 10: Intro to BiologyInstructor: Paul Nagami

Laney College

Sept. 13, 2013

Structure and Function of Cells, Part 2: Energy and

CellFunction

Agenda

• Administrative Stuff• A Quick Review: Cells as Bags of

Bags• The Great Cat and Rat Farm• Energy, Entropy, Calories, and ATP• Diffusion and Osmosis• Getting Molecules into and out of

the Cell• Wrap-up

The Cell: A Biological Bag

Cells are lipids, proteins, nucleic acids, and carbohydrates in a bag, or plasma membrane!

Two layers of lipids!

Proteins can act as channels, signal receivers, and so on!

Phospholipid bilayer+

x 2 layers!

Organelles: Bags with Functions

But where do these parts get the energy to perform their functions? What is energy, anyway?

Our Cells Need Energy To…

The Great Cat and Rat FarmIn a classic tall tale, someone starts a “cat and rat farm.” At this farm, they raise cats for fur…

…and raise rats to feed to the cats. The cats eat the rats.

But what do the rats eat?

When the owner’s done getting the fur from the cats….

…they feed them to the rats!

This is impossible. But why? Explain in terms of energy.

EnergyEnergy is the capacity to do work. In science, work generally means moving things around.

Moving objects have kinetic energy. Energy that is being “stored” in an object’s position or chemical structure (electrons) is called potential energy.

Lipids and carbohydrates can store a lot of potential energy as chemical energy. When oxygen grabs electrons from these substances, energy is released!

Which releases more energy when burned – a gram of glucose, or a gram of TNT?

Conservation of Energyheat

heat

heat heat

Entropy (or, Not All Energy Is Equally Useful)

Measuring Energy

We can measure the energy in food by burning it, transferring its chemical energy as heat.

Increase in temperature = molecules moving faster

Amount of energy needed to make 1 gram of water 1 degree hotter = 1 calorie

How Does Energy from Food Move Your Muscles?

ATP: A Cellular “Battery”

ADP can then be recycled into ATP by putting the phosphate back on, starting the cycle over.Can this cycle simply be repeated over and over to

generate energy? Explain on your index card.

Mitochondria

Recycle ADP into ATP using energy from other chemicals.Convert the chemical energy of food into a “concentration gradient,” which is used to make ATP from ADP

…But what’s a concentration gradient? What does it have to do with energy? How can it drive our bodies?

(There are other ways of making ATP, but let’s focus here for now.)

Diffusion (Spreading Out)

By random motion, molecules have a tendency to spread out. They will tend to go from places where there are lots of them to places where there are few of them. It’s luck!

When substances move from higher concentration to lower concentration, we call that “moving down a concentration gradient.”

This movement releases energy, which can be used to do work! In mitochondria, differences in H+

across the “folds” are used to drive the making of ATP from ADP.

But What If We Want to Reverse Diffusion?

Movement against a concentration gradient is active transport. It requires the input of energy (ATP -> ADP).

Osmosis: Movement of Solute across a Membrane

Functional Effects of Osmosis

When Channels Aren’t Enough

Exocytosis

Exo = outside/out of

Cyto = cell

Endocytosis

Endo = inside/into

Cyto = cell

Review!