Cells and how they work Chapter 3

CELLS AND HOW THEY WORK Chapter Outline Cells: Organized for life The cytoskeleton: support and movement The plasma membrane: a lipid bilayer The plasma membrane is a mix of lipids and proteins Membrane proteins carry out most membrane functions DNA is organized in chromosomes Endoplasmic reticulum (ER) : A protein and lipid assembly line Golgi Bodies: Packing and shipping Mitochondria: the cell’s energy factories

Mitochondria: the cell’s energy factories ATP—The cell’s energy currency How cells make ATP Cells make ATP in three steps Step 1: Glycolysis breaks glucose down to pyruvate Step 2: The Krebs cycle produces energy-rich transport molecules Step 3: Electron transport produces a large harvest of ATP

Smallest unit of life Can survive on its own or has potential to do so Is highly organized for metabolism Senses and responds to environment Has potential to reproduce Cell

Structure of Cells All start out life with: –Plasma membrane –Region where DNA is stored –Cytoplasm Two types: –Prokaryotic –Eukaryotic

PLASMA MEMBRANE GOLGI BODY LYSOSOME ENDOPLASMIC RETICULUM (ER) nuclear envelope nucleolus NUCLEUS MITOCHONDRION

microfilaments microtubules components of cytoskeleton plasma membrane mitochondrion nuclear envelope nucleolus DNA + nucleoplasm NUCLEUS vesicle lysosome rough ER ribosomes smooth ER vesicle Golgi body pair of centrioles

Table 3.2 Common Features of Eukaryotic Cells ORGANELLES AND THEIR MAIN FUNCTIONS: Nucleus Endoplasmic reticulum (ER) Golgi body Various vesicles Mitochondria Contains the cell’s DNA Routes and modifies newly formed polypeptide chains; also, where lipids are assembled Modifies polypeptide chains into mature proteins; sorts and ships proteins and lipids for secretion or for use inside cell Transport or store a variety of substances; break down substances and cell structures in the cell; other functions Produce ATP

Table 3.2 Common Features of Eukaryotic Cells OTHER STRUCTURES AND THEIR FUNCTIONS: Ribosomes Cytoskeleton Assemble polypeptide chains Gives overall shape and internal organization to cell; moves the cell and its internal parts

Electron Microscope Light Microscope

Basis for cell shape Enables organelle movement within cells and, in some cases, cell motility Main elements are microtubules, microfilaments, and filaments Cytoskeleton

microtubules intermediate filaments microfilaments Figure 3.13

Flagella and Cilia Structures for cell motility 9+2 internal structure Arise from centrioles dynein microtubule

one of the outer ring’s pairs of microtubules (doublets) dynein arm two central microtubules central sheath base of flagellum or cilium plasma membrane basal body plasma membrane

Main component of cell membranes Gives membrane its fluid properties Two layers of phospholipids –Hydrophilic heads face outward –Hydrophobic tails in center Lipid Bilayer

lipid bilayer water

one layer of lipids

Plasma Membrane Extremely thin Mosaic of proteins and lipids Lipids give membrane its fluid quality Proteins carry out most membrane functions

Membrane Proteins Transport proteins Receptor proteins Recognition proteins Adhesion proteins

EXTRACELLULAR FLUID cytoskeletal proteins just beneath the plasma membrane adhesion protein phospholipid cholesterol LIPID BILAYER recognition protein receptor protein CYTOPLASM transport proteins

In-text figure Page 50 oxygen, carbon dioxide, and other small, nonpolar molecules; some water molecules glucose and other large, polar, water-soluable molecules; ions (e.g., H +, Na +, K +, Ca ++, CI – )

Membrane Proteins Transport proteins Receptor proteins Recognition proteins Adhesion proteins

glucose, more concentrated outside cell than inside glucose transporter When the glucose binding site is again vacant, the protein resumes its original shape. Glucose binds to a vacant site inside the channel through the transport protein. Glucose becomes exposed to fluid on the other side of the membrane. Bound glucose makes the protein change shape. Part of the channel closes behind the solute.

Passive Transport Flow of solutes through the interior of passive transport proteins down their concentration gradients Passive transport proteins enable solutes to move both ways Does not require any energy input

Active Transport Net diffusion of solute is against concentration gradient ATP gives up phosphate to activate protein Binding of ATP changes protein shape and affinity for solute

higher concentration of calcium outside cell lower concentration of calcium inside cell The pump returns to its resting shape. ATP binds to a calcium pump. Shape change permits calcium release at opposite side of membrane. Phosphate group and ADP are released. Calcium enters tunnel through pump. ATP transfers a phosphate group to pump. This energy input will cause pump’s shape to change.

Components of Nucleus Nuclear envelope Nucleoplasm Nucleolus

nuclear pore (protein complex that spans both lipid bilayers) one of two lipid bilayers (facing cytoplasm) one of two lipid bilayers (facing nucleoplasm) NUCLEAR ENVELOPE

Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells Functions of Nucleus

Endoplasmic Reticulum In animal cells, continuous with nuclear membrane Extends throughout cytoplasm Two regions: rough and smooth

Rough ER Arranged into flattened sacs Ribosomes on surface give it a rough appearance Some polypeptide chains enter and are modified

cytoplasmribosome vesicle RNA messages from the nucleus the cell nucleus rough ER

Smooth ER A series of interconnected tubules No ribosomes on surface Lipids assembled inside tubules

Golgi Bodies Put finishing touches on proteins and lipids that arrive from ER Package finished material for shipment to final destinations

internal space budding vesicle

5 Vesicles from the Golgi body transport products to the plasma membrane. Products are released by exocytosis. 4 Proteins and lipids take on final form inside Golgi body. Modifications enable them to be sorted out and shipped to proper destinations. 3 Vesicles bud from the ER membrane and transport unfinished proteins and lipids to a Golgi body. 2 In the membrane of smooth ER, lipids are assembled. 1 Some polypeptide chains enter the rough ER. Modifications begin. Endocytic vesicles form at plasma membrane and move into the cytoplasm. They might fuse with the membrane of other organelles or remain intact, as storage vesicles. Exocytic vesicles bud from ER and Golgi membranes, travel to and fuse with plasma membrane. Their contents are thereby released from the cell. DNA instructions for building polypeptide chains leave the nucleus and enter the cytoplasm. assorted vesicles Golgi body smooth ER rough ER Chains are assembled on ribosomes in cytoplasm.

Vesicles Membranous sacs that move through the cytoplasm Lysosomes Peroxisomes

©2005 Brooks/Cole - Thomson plasma membrane endocytic vesicle forming exocytic vesicle leaving cytoplasm

Mitochondrial Structure Outer membrane faces cytoplasm Inner membrane folds back on itself Membranes form two distinct compartments ATP-making machinery is embedded in the inner mitochondrial membrane

ATP-producing powerhouses Double-membrane system Carry out the most efficient energy-releasing reactions Reactions require oxygen Mitochondria

cristae inner membrane outer mitochondrial membrane outer compartment inner compartment

outer compartmentcytoplasm outer mitochondrial membrane inner mitochondrial membrane

Glucose is absorbed into blood Pancreas releases insulin Insulin stimulates glucose uptake by cells Cells convert glucose to glucose-6-phosphate This traps glucose in cytoplasm where it can be used for glycolysis Carbohydrate Breakdown and Storage

Glycolysis Occurs in cytoplasm Reactions are catalyzed by enzymes Glucose2 Pyruvate (six carbons) (three carbons)

ATP Universal Energy Currency ATP is earned in reactions that yield energy, and spent in reactions that require it P PP ribose adenine

Mitochondrial Reactions Reactions begin when pyruvate enters a mitochondrion

How Cells Make ATP Step 3: Electron transport produces many ATP molecules. –The final stage of cellular respiration occurs in the electron transport systems embedded in the inner membranes (cristae) of the mitochondrion.

Glucose ATP ADP P PP PP Energy in (2 ATP) Net Energy Yield: 2 PGAL: pyruvate NAD + NADH Intermediates donate phosphate to ADP, making 4 To second set of reactions

CYTOPLASM MITOCHONDRION GLYCOLYSIS ELECTRON TRANSPORT PHOSPHORYLATION KREBS CYCLE ATP energy input to start reactions 2 CO 2 4 CO water 2 NADH 8 NADH 2 FADH 2 2 NADH2 pyruvate e - + H + e - + oxygen (2 ATP net) glucose TYPICAL ENERGY YIELD: 36 ATP e-e- e - + H + ATP H+H+ e - + H + ATP2 4

Overview of Aerobic Respiration C 6 H O 2 6CO 2 + 6H 2 0 glucose oxygen carbon water dioxide

Creating an H + Gradient NADH OUTER COMPARTMENT INNER COMPARTMENT

Making ATP ATP ADP + P i INNER COMPARTMENT

How Electron Transport Forms ATP

©2005 Brooks/Cole - Thomson Krebs Cycle NADH ATP ADP + P i INNER COMPARTMENT OUTER COMPARTMENT acetyl-CoA free oxygen 6 H + flows back into inner compartment, through ATP synthases. Flow drives ATP formation. 1 Pyruvate from cytoplasm enters inner mitochondrial compartment. 3 NADH and FADH 2 give up electrons and H + to electron transport systems. 2 Krebs cycle and preparatory steps: NAD + and FADH 2 accept electrons and hydrogen. ATP forms. Carbon dioxide forms. 5 Oxygen accepts electrons, joins with H + to form water. 4 As electrons move through the transport system, H + is pumped to outer compartment.

Summary of Energy Harvest (per molecule of glucose) Glycolysis –2 ATP formed by substrate-level phosphorylation Krebs cycle and preparatory reactions –2 ATP formed by substrate-level phosphorylation Electron transport phosphorylation –32 ATP formed

Diffusion

Click to view animation. Animation

Factors Affecting Diffusion Rate Concentration gradient Molecular size Temperature Electrical or pressure gradients

selectively permeable membrane between two compartments protein molecule water molecule Osmosis

98% water 2% sucrose 100% water (distilled) 90% water 10% sucrose 98% water 2% sucrose HYPOTONIC CONDITIONS HYPERTONIC CONDITIONS ISOTONIC CONDITIONS

Enzyme Structure and Function Enzymes speed the rate at which certain reactions occur Nearly all are proteins An enzyme recognizes and binds to only certain substrates Reactions do not alter or use up enzyme molecules

Participants in Metabolic Pathways Enzymes Energy Carriers Cofactors Substrates Intermediates End Products

Factors Influencing Enzyme Activity Temperature pH Salt concentration Coenzymes and cofactors

product molecule ©2005 Brooks/Cole - Thomson two substrate molecules active site substrates contacting active site of enzyme substrates briefly bind tightly to enzyme active site enzyme unchanged by the reaction