The Working Cell

ATP & Cellular Work

Enzymes

Membrane Function

Chemical Energy

Chemical EnergyWhere do our muscles get energy to perform work?

From food we eat

When body breaks down food molecules what happens?

Energy from food molecules is stored

Potential energy

Can be converted to kinetic energy

Or, muscle activity

When, how is stored energy released?

During the process of cellular respiration

What does cell respiration do?Converts chemical energy (food)

To another form of energy: ATP

What is the significance of ATP?

More cellular respiration and ATP in Chapter 6

Food

Cell respiration

?

? ?

Energy for cellular work

Muscle work

?

?

How much energy do we get to use for cellular work?

The diagram gives us a clue

What percent is given off as heat?

What percent is captured as ATP?

~60%

~40%

What is the ~60% heat converted to?

Food Calories

– is the amount of energy – that raises the temperature – of one gram (g) of water

– by one degree (1) Celsius

What is a calorie? A unit of energy

And, how is it measured?

How much energy is in this

handful of peanuts? Enough to boil a quart of water!

(in kilocalories)(as fuel for energy)

The kilocalorie (Kcal or C) is 1,000 calories• The unit used to measure the energy in food

Pizza!

What would you have to do to burn off the calories from this

pizza?

You’d have to run about 14 miles!

ATP

Why is ATP so important? It ‘powers’ all cellular work

How? • It releases ‘free’ energy

(adenosine triphosphate)

• When its phosphate bonds are hydrolyzed

(or, broken down)

What is ATP? It is a nucleotide that performs many essential roles in the cell

Phosphate ‘tail’

What does the ATP structure look like?

Adenosine

Ribose sugar

ATP is broken down to ADP

+

Accompanied by release of energy

ADP? (adenosine diphosphate)

Where’s the power in ATP?

Unstable. Why?

Repulsion between negatively charged phosphate groups

In the phosphate tail

Release of last P makes energy available

(adenosine diphosphate)

What about that ‘leftover’ phosphate?

Its used to energize other molecules

What do these other molecules do?

Help cells do 3 main types of work

• Mechanical • Transport• Chemical

ATP and Mechanical Work?

Phosphate transferred to special motor proteins

(muscles)

What happens then?Proteins change shape

Muscle cells contractPerform mechanical work

ATP and Transport Work?

Phosphate transferred to brain cells

What happens then?Ions pumped across membranes

ATP and Chemical Work?

Make cell’s giant molecules

What happens then?Amino acids are linked to make a protein

Via a dehydration reaction

Reactants Products

What is the ATP cycle?

Our cells need energy (ATP) all the time!

Its recyclable!

Cellular respiration

Food

Energy in…

To regenerate ATP

Energy out…

For cellular work

The 3rd phosphate

Acts as an energy shuttle

Learning check

1. What is the source of energy for regenerating ATP from ADP?

2. A kilocalorie is equal to _______?

3. Most cellular work is accomplished by _____ energizing molecules by _____ them.

a. enzymes ... activating

b. diffusion ... activating

c. substrates ... transferring a phosphate group to

d. ATP ... transferring a phosphate group to

Enzymes What is the barrier for reactions to occur?

Energy must be added

What is this energy called?

Energy of activation EA

How does the cell overcome the barrier?Uses a specialized protein, an enzyme

What does the enzyme do?Serves as a biological catalystIncreases the rate of the reaction

‘lowers the energy barrier’Reduces activation energy

• Binds to specific molecules (substrates)

• Puts them under physical or chemical stress

• Which makes it easier to break bonds

• And start a reaction

What are the details?

• Enzyme very selective

• At the enzymes active site

Induced fit?

sucrase

Substrate ? Sucrose

What is this site?

What are these molecules?

Identify the steps?1. Enzyme available with empty active site

2. Substrate binds to enzyme

3. Substrate converted to products

4. Products are released

What are enzyme inhibitors?

‘Imposters’ that plug up the active site

Or at some remote site

How do they function?

Binding changes the shape of the enzyme

Active site no longer receptive

Examples of enzyme inhibitors?

Poisons e.g., malathion

Antibiotics

Inhibits an enzyme required for normal function of the insect nervous system

e.g., penicillin

Inhibits an enzyme bacteria use to make cell walls

Membrane Function

1. Endocytosis moves materials _____ a cell via _____.

a. into ... facilitated diffusion

b. into ... membranous vesicles

c. into ... a transport protein

d. out of ... diffusion

e. out of ... membranous vesicles

2. What name is given to the process by which water crosses a selectively permeable membrane?

a. diffusion

b. passive transport

c. phagocytosis

d. pinocytosis

e. osmosis

3. Active transport ______.

a. Can move solutes against their concentration gradient

b. Can involve the transport of ions

c. Requires the cell to expend energy

d. Uses ATP as an energy source

e. All of the above

2. A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mothers milk. These molecules probably enter the cells lining the baby’s digestive tract via ____________?

a. osmosis

b. passive transport

c. exocytosis

d. active transport

e. endocytosis

Hydrolysis Decomposition of a substance by the insertion of water molecules between certain of its bonds. Food is digested by hydrolysis.

protein A three-dimensional biological polymer constructed from a set of 20 different monomers called amino acids.

enzyme A protein serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction.

substrate The reactant on which an enzyme works.

active site The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.