CHAPTER 1

CELL STRUCTURE AND FUNCTION

CHAPTER 1

CELL STRUCTURE AND FUNCTION

PRELECTURE QUIZ (TRUE FALSE)

The endoplasmic reticulum is the control center of the cell.

Cells communicate with each other by means of chemical messenger systems.

The glycolytic pathway does not require oxygen to produce cellular energy.

Examples of passive movement across the cell membrane include diffusion, osmosis, and active transport.

Cells with a similar embryonic origin or function are often organized into larger functional units called tissues.

F

T

T

F

T

PRELECTURE QUIZ __________ tissue is the most abundant

tissue type in the body. Three types of __________ tissue exist:

skeletal, cardiac, and smooth. __________ literally means “cell

eating” and involves the engulfment and subsequent killing or degradation of microorganisms and other particulate matter.

The __________ serve as sites of protein synthesis in the cell.

Cell metabolism is the process that converts carbohydrates, proteins, and fats into __________, which is the major source of energy for all body cells.

ATP

Connective

muscle

Phagocytosis

Ribosomes

CELL STRUCTURE

CELL COMPONENTS Nucleus and nucleolus Cytoplasm and cytoplasmic

organelles Ribosomes Endoplasmic reticulum Golgi complex Lysosomes, peroxisomes Mitochondria

Cytoskeleton Microtubules, microfilaments

THE PLASMA MEMBRANE

RED BLOOD CELLS START OUT WITH ALL THE ORGANELLES

As they mature, they: Lose their lysosomes Produce hemoglobin Have small Golgi bodies Have enlarged endoplasmic

reticulum

When they are mature, they: Lose their endoplasmic reticulum Lose their mitochondria

How does this relate to their function?How does this relate to their function?

QUESTION

By the time a red blood cell (RBC) is mature, it has lost all but which of the following?

a. lysosomes

b. endoplasmic reticulum

c. hemoglobin

d. mitochondria

ANSWER

c. Hemoglobin

Because the function of the RBC is to carry oxygen, hemoglobin is an essential component of the cell (each hemoglobin molecule can carry four molecules of oxygen) . Lysosomes, endoplasmic reticulum, and mitochondria all exert some metabolic function in other cells. But, if they remained in the RBC, the oxygen on board would be consumed before reaching its destination.

ANAEROBIC ENERGY METABOLISM—GLYCOLYSIS

In the cytoplasm, molecules are broken into chunks, 2-carbons each Glycolysis breaks sugar 2 ATP molecules

formed Other pathways break fatty acids or amino

acids Breaking molecules involves removing electrons

º Which are handed to electron carriers like NAD and FAD

º H+ follow the electrons Afterwards, they are put back on the 2-carbon

chunksº Forming lactic acid

AEROBIC ENERGY METABOLISM—KREBS CYCLE

2-carbon molecules enter the mitochondrion matrix space Krebs cycle breaks them

down 1 ATP molecule formed

Carbon is lost as CO2

Energy is extracted from nutrients and used to form ATP from ADP

Energy is released to do cellular work when ATP is broken back down to ADP

The 2-Carbon molecules don’t make lactic acid but

KREBS CYCLE OCCURS WITHIN MITOCHONDRIA

• Breaking molecules involves removing electrons

– Handed to electron carriers like NAD and FAD

– H+ follows the electrons

– Many of these electron carriers are loaded up with electrons by the Krebs cycle

QUESTION

Tell whether the following statement is true or false:

ATP is produced in the mitochondria.

ANSWER

True

The Krebs cycle occurs in the mitochondria. Each Krebs cycle produces one molecule of ATP.

DIFFUSION IS MOVEMENT OF MOLECULES

Passive diffusion: molecules move randomly away from the area where they are most concentrated

Facilitated diffusion: molecules diffuse across a membrane by passing through a protein

Osmosis: diffusion of water molecules

QUESTION

Your patient has been given an intravenous solution of water. What will happen to this patient’s red blood cells?

a. They will burst/lyse.b. They will shrink.c. They will not be affected by the water

solution.

ANSWER

a. They will burst/lyse.

Osmosis causes movement from “more watery” to “less watery.” Because water is “more watery” than the RBC (it’s water, after all), water moves into the cell, causing it to expand and burst/lyse.

CELL COMMUNICATION

A messenger molecule attaches to receptor proteins on cell surface

Receptor proteins cause cell to respond by: Opening ion channels to let ions in or out Causing a second molecule to be

released inside the cell Turning on enzymes inside the cell Stimulating the transcription of genes in

the nucleus

THE BASICS OF CELL FIRING Cells begin with a

negative charge: resting membrane potential

Stimulus causes some Na+ channels to open

Na+ diffuses in, making the cell more positive

THE BASICS OF CELL FIRING (CONT.)

At threshold potential, more Na+ channels open

Na+ rushes in, making the cell very positive: depolarization

Action potential: the cell responds (e.g., by contracting)

THE BASICS OF CELL FIRING (CONT.)

K+ channels open K+ diffuses out, making

the cell negative again: repolarization

Na+/K+ ATPase removes the Na+ from the cell and pumps the K+ back in

QUESTION

Tell whether the following statement is true or false:

An action potential is the result of K+ movement out of the cell.

ANSWER

FalseAn action potential occurs when Na+

moves into the cell, making it more positive on the inside (depolarization). When K+ leaves the cell, it becomes less positive (more negative) until it returns to resting membrane potential (repolarization).

Na+ enters cell and muscle cell

depolarizes

Ca2+ released from sarcoplasmic reticulum into the

sarcoplasm

Ca2+ attaches to

troponin

MUSCLE CONTRACTION

QUESTION

What happens to the sarcomere when myosin slides across the actin binding sites?

a. It gets longer.b. It gets shorter.c. There is no change in length.d. It releases acetylcholinesterase.

ANSWER

a. It gets shorter.When the myosin binds with exposed

actin sites (myosin “reaches” forward like your hands do when pulling end-over-end on a rope), the Z lines get pulled closer together, and the muscle cell shortens/contracts.