Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 1 Cell Structure and Function

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cell Structure Endoplasmic reticulum Golgi apparatus Nucleolus Lysosome Ribosomes Mitochondrion Cell membrane Nucleus

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cell Components Nucleus and nucleolus Cytoplasm and cytoplasmic organelles –Ribosomes –Endoplasmic reticulum –Golgi complex –Lysosomes, peroxisomes –Mitochondria Cytoskeleton –Microtubules, microfilaments

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Hemoglobin Rationale: 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Anaerobic Energy Metabolism—Glycolysis In the cytoplasm, molecules are broken into 2-carbon chunks –Glycolysis breaks sugar  2 ATP molecules formed –Other pathways break fatty acids or amino acids –Breaking molecules involves removing electrons ºHanded to electron carriers like NAD and FAD ºH + follows the electrons –Afterwards, they are put back on the 2-carbon chunks ºForming lactic acid

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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 CO 2

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. ATP is produced in the mitochondria.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True Rationale: The Krebs cycle occurs in the mitochondria. Each Krebs cycle produces one molecule of ATP.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Aerobic Energy Metabolism—Oxidative Phosphorylation Inside mitochondrion matrix: Many electron carriers carry electrons Many H + ions follow them, attracted to the negative electrons In inner mitochondrial membrane: Proteins that can carry electrons cross the membrane And that can make ATP when H + ions pass through them

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Aerobic Energy Metabolism—Oxidative Phosphorylation (cont.) Electron carriers pass electrons to the membrane proteins H + ions follow the electrons across the membrane, but the electrons are passed back into the mitochondrion electrons H+H+ H+H+ H+H+ H+H+ H+H+ H+H+

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Aerobic Energy Metabolism—Oxidative Phosphorylation (cont.) H + ions are attracted to the electrons but can only get back into the mitochondrion by going through the ATP-producing protein This is how most ATP is made electrons H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Aerobic Energy Metabolism—Oxidative Phosphorylation (cont.) Now the H + ions are reunited with the electrons inside the mitochondrion They combine with oxygen to form H 2 O electrons H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ oxygen

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Basic Energy Metabolism—What Three Points Would You Add to This Diagram?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Osmosis: Which Way Will Water Move? Blood: Few solutes Lots of water Cell: Many solutes Less water

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Water Diffuses From the Place With Lots of Water to the Place With Less Water Blood: Few solutes Lots of water Cell: Many solutes Less water

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins “Water Follows Solutes” Blood: Few solutes Lots of water Cell: Many solutes Less water

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Na + Diffuses into a Cell—What Will Water Do? Na +

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins The Cell’s Na + /K + ATPase Pumps the Na + Back Out—What Will Water Do Now? 3 Na + 2 K +

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer a.They will burst/lyse. Rationale: 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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 Threshold potential Resting membrane potential Stimulus Action potential

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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) Threshold potential Resting membrane potential Stimulus Action potential

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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 Threshold potential Resting membrane potential Stimulus Action potential

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. An action potential is the result of K + movement out of the cell.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Rationale: An 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).

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Acetylcholine (ACh) Starts Contraction What will happen if ACh receptors are destroyed? What will happen if you block acetylcholinesterase? acetylcholine released from motor neuron attaches to receptor on muscle cell opens Na + gates acetylcholinesterase destroys acetylcholine and stops the firing Na + enters cell and muscle cell depolarizes

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Na + enters cell and muscle cell depolarizes Ca 2+ released from sarcoplasmic reticulum into the sarcoplasm Ca 2+ attaches to troponin

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Ca 2+ attaches to troponin troponin and tropomyosin move off actin binding site myosin attaches to actin binding site

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Contraction Uses Energy Myosin uses ATP to pull actin It also needs ATP to let go of actin Why does a dead body become stiff? myosin attaches to actin binding site myosin uses energy from ATP to pull actin myosin picks up a new molecule of ATP myosin lets go of actin and reaches forward

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b.It gets shorter. Rationale: 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.