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Exam 2 Review Slides Lectures 5-8 Chapters 3 and 22 (Sec. 22.1-22.4) Cell Membranes Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 2 Passage of Materials through the Cell Membrane Carrier/channel proteins required for all but fatsoluble molecules and small uncharged molecules oxygen, carbon dioxide and other lipid-soluble substances diffuse freely through the membrane 3 Cellular Organelles Table 1 of 2 CELL COMPONENT DESCRIPTION/ STRUCTURE FUNCTION(S) CELL MEMBRANE Bilayer of phospholipids with proteins dispersed throughout cell boundary; selectively permeable (i.e. controls what enters and leaves the cell; membrane transport) CYTOPLASM jelly-like fluid (70% water) suspends organelles in cell NUCLEUS Central control center of cell; bound by lipid bilayer membrane; contains chromatin (loosely colied DNA and proteins) controls all cellular activity by directing protein synthesis (i.e. instructing the cell what proteins/enzymes to make. NUCLEOLUS dense spherical body(ies) within nucleus; RNA & protein Ribosome synthesis RIBOSOMES RNA & protein; dispersed throughout cytoplasm or studded on ER protein synthesis ROUGH ER Membranous network studded with ribosomes protein synthesis SMOOTH ER Membranous network lacking ribosomes lipid & cholesterol synthesis GOLGI “Stack of Pancakes”; cisternae modification, transport, and packaging of proteins 4 Cellular Organelles Table 2 of 2 CELL COMPONENT DESCRIPTION/ STRUCTURE FUNCTION(S) LYSOSOMES Membranous sac of digestive enzymes destruction of worn cell parts (“autolysis) and foreign particles PEROXISOMES Membranous sacs filled with oxidase enzymes (catalase) detoxification of harmful substances (i.e. ethanol, drugs, etc.) MITOCHONDRIA Kidney shaped organelles whose inner membrane is folded into “cristae”. Site of Cellular Respiration; “Powerhouse of Cell” FLAGELLA long, tail-like extension; human sperm locomotion CILIA short, eyelash extensions; human trachea & fallopian tube to allow for passage of substances through passageways MICROVILLI microscopic ruffling of cell membrane increase surface area CENTRIOLES paired cylinders of microtubules at right angles near nucleus aid in chromosome movement during mitosis 5 Cell Death • Two mechanisms of cell death – Necrosis – Programmed cell death (PCD or apoptosis) • Necrosis – Tissue degeneration following cellular injury or destruction – Cellular contents released into the environment causing an inflammatory response • Programmed Cell Death (Apoptosis) – Orderly, contained cell disintegration – Cellular contents are contained and cell is immediately phagocytosed 6 Stem and Progenitor Cells Stem cell • can divide to form two new stem cells • can divide to form a stem cell and a progenitor cell • totipotent – can give rise to any cell type (Embryonic stem cells) • pluripotent – can give rise to a restricted number of cell types Progenitor cell • committed cell • can divide to become any of a restricted number of cells • pluripotent 7 8 Cancer Two types of tumors • benign – usually remains localized • malignant – invasive and can metastasize; cancerous Genes that cause cancer • oncogenes – activate other genes that increase cell division • tumor suppressor genes – normally regulate mitosis; if inactivated they will not regulate mitosis Oncology is the study of tumors 9 Cancer Metastasis is the spread of a cancer from its site of origin to other areas of the body 10 Lecture Review TRANSPORT PROCESS IS ENERGY NEEDED? CONCENTRATION GRADIENT GENERAL DESCRIPTION EXAMPLE IN HUMANS SIGNIFICANCE SIMPLE DIFFUSION NO [HIGH] TO [LOW] spreading out of molecules to equilibrium O2 into cells; CO2 out of cells. Cellular Respiration FACILITATED DIFFUSION NO [HIGH] TO [LOW] Using a special cm carrier protein to move something through the cell membrane (cm) Process by which glucose enters cells OSMOSIS NO [HIGH] TO [LOW] water moving through the cm to dilute a solute maintenance of osmotic pressure of 0.9%. Same FILTRATION NO [HIGH] TO [LOW] using pressure to push something through a cm (sprinkler hose) manner in which the kidney filters things from blood removal of metabolic wastes 11 Lecture Review TRANSPORT PROCESS IS ENERGY NEEDED? CONCENTRATION GRADIENT GENERAL DESCRIPTION EXAMPLE IN HUMANS ACTIVE TRANSPORT YES [LOW] TO [HIGH] opposite of diffusion at the expense of energy K+-Na+-ATPase pump maintenance of the resting membrane potential ENDOCYTOSIS YES [LOW] TO [HIGH] bringing a substance into the cell that is too large to enter by any of the above ways; Phagocytosi: cell eating; Pinocytosis: cell drinking. Phagocytosed (foreign) particles fuse with lysosomes to be destroyed help fight infection EXOCYTOSIS YES [LOW] TO [HIGH] expelling a substance from the cell into ECF Exporting proteins; dumping waste Same SIGNIFICANCE 12 Osmotic Pressure/Tonicity Osmotic Pressure (Osmolarity) – ability of solute to generate enough pressure to move a volume of water by osmosis *Osmotic pressure increases as the number of nonpermeable solutes particles increases 0.9% NaCl • isotonic – same 5.0% Glucose osmotic pressure as a second solution • hypertonic – higher osmotic pressure • hypOtonic – lower osmotic pressure Crenation The O in o hyp tonic 13 Some Definitions… *Chromatin – combination of DNA plus histone proteins used to pack DNA in the cell nucleus Gene – segment of DNA that codes for a protein or RNA - About 30,000 protein-encoding genes in humans - DNA’s instructions are ultimately responsible for the ability of the cell to make ALL its components Genome – complete set of genes of an organism - Human Genome Project was complete in 2001 - Genomes of other organisms are important also Genetic Code – method used to translate a sequence of nucleotides of DNA into a sequence of amino acids 14 Structure of Nucleic Acids Purines: Adenine and Guanine (double ring) Pyrimidines: Cytosine, Thymine, and Uracil (single ring) Figure from: Alberts et al., Essential Cell Biology, Garland Press, 1998 15 Structure of DNA 5' 3' A double-stranded DNA molecule is created by BASEPAIRING of the nitrogenous bases via HYDROGEN bonds. Notice the orientation of the sugars on each stand. 5' 3' *DNA is an antiparallel, double-stranded polynucleotide helix16 Structure of DNA Complementary base pairing… Base pairing in DNA is VERY specific. - Adenine only pairs with Thymine (A-T) - Guanine only pairs with Cytosine (G-C) Note that there are: - THREE hydrogen bonds in G-C pairs - TWO hydrogen bonds in A-T pairs - A purine (two rings)base hydrogen bonds with a pyrimidine base (one ring) Figure from: Martini, “Human Anatomy & Physiology”, Prentice Hall, 2001 17 DNA Replication 5’ THINGS TO NOTE: 1. DNA is replicated in the S phase of the cell cycle 3’ 5’ 3’ 3. DNA polymerase has a proofreading function (1 mistake in 109 nucleotides copied!) 5’ 3’ 3’ 5’ 3’ Figure from: Martini, “Human Anatomy & Physiology”, Prentice Hall, 2001 2. New strands are synthesized in a 5’ to 3’ direction 5’ 4. Semi-conservative replication describes pairing of postreplication strands of DNA (1 new, 1 old) 18 RNA • RNA is a polynucleotide with important differences from DNA – Uses Uracil (U) rather than Thymine (T) – Uses the pentose sugar, ribose – Usually single-stranded • There are three important types of RNA – mRNA (carries code for proteins) – tRNA (the adapter for translation) – rRNA (forms ribosomes, for protein synthesis) 19 Transciption/Translation • Transcription – generates mRNA from DNA – Occurs in nucleus of the cell – Uses ribonucleotides to synthesize mRNA • Translation – generates polypeptides (proteins) from mRNA – Occurs in the cytoplasm of the cell – uses tRNA and ribosomes 20 The Genetic Code 1. Codon – group of three ribonucleotides found in mRNA that specifies an aa 2. Anticodon – group of three ribonucleotides found in tRNA that allows specific hydrogen bonding with mRNA 3. AUG is a start codon and also codes for MET. UAA, UAG, and UGA are stop codons 21 that terminate the translation of the mRNA strand. Find the AMINO ACID SEQUENCE that corresponds to the following gene region on the DNA: Template -> G A T T G A A T C Coding -> C T A A C T T A G tRNAs Transfer RNAs (tRNA) function as ‘adapters’ to allow instructions in the form of nucleic acid to be converted to amino acids. Figures from: Martini, Anatomy & Physiology, Prentice Hall, 2001 23 Eukaryotic Genes The template strand of DNA is the one that’s transcribed. The coding strand of DNA is used as the complementary strand for the template strand in DNA and looks like the codons. Figure from: Alberts et al., Essential Cell Biology, Garland Publishing, 1998 24 Eukaryotic mRNA Modification Newly made eukaryotic mRNA molecules (primary transcripts) undergo modification in the nucleus prior to being exported to the cytoplasm. 1. Introns removed 2. 5' guanine cap added 3. Poly-A tail added Figure from: Alberts et al., Essential Cell Biology, Garland Publishing, 1998 25 The Fate of Proteins in the Cell • Breakdown of proteins regulates the amount of a given protein that exists at any time. • Each protein has unique lifetime, but the lifetimes of different proteins varies tremendously. • Proteins with short life-spans, that are misfolded, or that become oxidized must be destroyed and recycled by the cell. Enzymes that degrade proteins are called proteases. They are hydrolytic enzymes. Most large cytosolic proteins in eukaryotes are degraded by enzyme complexes called proteasomes. 26 Enzymes • Enzymes are biological catalysts – Highly specific for their substrate – Lower activation energy needed to start a reaction – Are not consumed during reaction – May require cofactors/coenzymes – Effectiveness is greatly affected by temperature, pH, and the presence of required cofactors Cofactors • make some enzymes active • ions or coenzymes Coenzymes • complex organic molecules that act as cofactors (so coenzymes ARE cofactors) • vitamins • NAD+ 27 Harnessing Energy from Carbohydrates General Reaction sequence in carbohydrate catabolism OXIDATION C6H12O6 + 6 O2 6 CO2 + 6 H2O + ENERGY REDUCTION Electrons (H·) “fall” in energy from organic molecules to oxygen during cellular respiration. That is, e- LOSE potential energy during this process and this energy is captured to make ATP However, electrons CANNOT be transferred directly from glucose to the electron transport chain. There are intermediates – activated carrier molecules 28 Energy for Metabolic Reactions Energy • ability to do work or change something (potential, kinetic) • heat, light, sound, electricity, mechanical energy, chemical energy • changed from one form to another, but NEVER destroyed (law of conservation of energy) • involved in all metabolic reactions Release of chemical energy • most metabolic processes depend on chemical energy • oxidation of glucose generates chemical energy • cellular respiration releases chemical energy slowly from molecules and makes it available for cellular use 29 Oxidation and Reduction Revisited Oxidation Is Loss of electrons; Oxidation Reduction Is Gain of electrons • gain of O2 “OIL RIG” • loss of e • loss of H (since a H carries an electron with it) • increase in oxidation number, e.g., Fe2+ -> Fe3+ Reduction • loss of O2 • gain of e• gain of H • decrease in oxidation number, e.g., Fe3+ -> Fe2+ 30 ATP – An Activated Carrier Molecule • each ATP molecule has three parts: • an adenine molecule These two components together are called a ? • a ribose molecule • three phosphate molecules in a chain • ATP carries its energy in the form or P (phosphate) • ATP is a readily interchangeable form of energy for cellular reactions (“common currency”) High-energy bonds 31 NAD(H) – An Activated Carrier Molecule NAD+ NAD (and NADP) are specialized to carry high-energy e- and H atoms A “packet” of energy = H· NADH + H+ NAD+ NADH These packets of energy will be passed to oxygen in the electron transport chain, and their energy used to drive the synthesis of ATP Important carriers of e- in catabolism: NADH, FADH2 Figure from: Alberts et al., Essential Cell Biology, Garland Press, 1998 32 Summary Table of Cell Respiration Where it takes place Products Produced Purpose What goes on GLYCOLYSIS TCA ETC Cytoplasm Mitochondria Mitochondria ATP NADH Pyruvate Breakdown of glucose (6 carbons) to 2 molecules of pyruvate (3 carbons) 1. Glucose is converted to pyruvate, which is converted to acetyl CoA when there is sufficient O2 present. 2. Acetyl CoA enters the TCA cycle. 3. If O2 is not present, pyruvate is converted to lactic acid to replenish the supply of NAD+ so glycolysis can continue to make ATP ATP NADH,FADH2 CO2 Generation of energy intermediates (NADH, FADH2, ATP) and CO2 ATP NAD,FAD H2O Generation of ATP and reduction of O2 to H2O(Recall that reduction is the addition of electrons) 1. The energy in acetyl CoA 1. Chemiosmosis (oxidative is trapped in activated phosphorylation) uses the carriers of electrons (NADH, electrons donated by NADH and FADH2) and activated FADH2 to eject H+ from the carriers of phosphate groups matrix of the mitochondria to the (ATP). intermembrane space. 2. The carries of electrons that trap the energy from 2. These H+ then flow down acetyl CoA bring their high their concentration gradient energy electrons to the through a protein (ATP synthase) electron transport chain. that makes ATP from ADP and phosphate. 3. During this process, the H+ that come through the channel in ATP synthase are combined with O2 to make H2O. 33 Summary of Catabolism of Proteins, Carbohydrates, and Fats Acetyl CoA is a common intermediate in the breakdown of most fuels. Acetyl CoA can be generated by carbohydrates, fats, or amino acids Acetyl CoA can be converted into fatty acids 34 Pyruvate is a Key Junction in Metabolism Lipogenesis Lipolysis * Glycogenolysis Glycogenesis Pyruvate is used to synthesize amino acids and Acetyl CoA Pyruvate can also be used to synthesize glucose via gluconeogenesis. Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 35 Carbohydrate Storage Excess glucose can be • stored as glycogen by glycogenesis (liver and muscle cells) • stored as fat by lipogenesis • converted to amino acids 36 Terms to Know… -olysis breakdown of -genesis creation of -neo new • Glycolysis – metabolism of glucose to pyruvate • Gluconeogenesis – metabolism of pyruvate to glucose (making CHO from non-CHO source) • Glycogenesis – metabolism of glucose to glycogen • Glycogenolysis – metabolism of glycogen to glucose • Lipogenesis – creation of new triglyceride (lipid, fat) • Lipolysis – breakdown of triglyceride into glycerol and fatty acids 37