LECTURE 5: THE WORKING CELL

I. Energy.

A. Major energy processes in cells.

1. Cellular respiration.

2. Photosynthesis.

B. Energy: "heat or anything that can be transformed into heat."

1. 1 cal = energy to raise the temp. of 1 gram of water from 14.5oC to 15.5oC.

2. Dieticians use kilocalories: 1 kcal = 1,000 cal.

C. Where are the calories?

1. Energy is in chemical bonds.

2. Breaking/forming chemical bonds requires energy.

D. Adenosine Triphosphate (ATP).

1. ATP is biologically usable energy — "energy currency" of the cell.

2. ATP is a nucleotide.

a. 5-carbon sugar (ribose).

b. a nitrogenous base (adenine).

c. 3 phosphate groups (each PO3).

3. High-energy phosphate bonds. (Figure 5.7)

4. The ATP cycle. (Figure 5.7)

a. ATP releases energy for cell use — produces ADP and P.

b. Energy released from food puts ADP and P together to make ATP.

E. What cells need energy for.

1. Mechanical work.

2. Transport.

3. Chemical reactions.

II. Plasma membrane processes.

A. Plasma membranes are selectively permeable.

B. Diffusion -- movement of molecules from high to region of low concentration.

1. Passive transport — no energy required.

2. Examples: CO2, O2, perfumes, etc.

C. Osmosis -- diffusion of water across a cell membrane.

1. Passive transport — no energy required.

2. Concentration of water depends on how much solute it contains.

3. Osmotic pressure.

D. Osmotic conditions for cells .

1. Isotonic environment.

2. Hypertonic environment.

3. Hypotonic environment

E. Osmoregulation (Figure 5.13).

F. Active transport — movement of molecules against the concentration gradient.

1. Moves molecules in the opposite direction of diffusion and osmosis.

2. Active transport requires energy to be expended by the cell.

3. Example: potassium.

4. Membrane proteins as "ion pumps" (Figure 5.15)

G. Endocytosis and Exocytosis.

1. Endocytosis: bringing particles into cells in vacuoles.

2. Exocytosis: expelling particles in vacuoles out of cells.

3. Both take energy to carry out. (Figure 5.16)

4. Kinds of endocytosis.

a. Phagocytosis — "cell eating." (Figure 5.17)

b. Pinocytosis — "cell drinking."

c. Receptor-mediated endocytosis.

H. Cell signaling.

1. Cells use chemical messengers (e.g. hormones) to communicate.

2. Membrane proteins act as receptors and initiate signal transduction.

3. Example: adrenalin (epinephrine) -- the "fight or flight hormone."

4. Figure 5.19.

NEXT TIME: Cellular Respiration. (Chapter 6)