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Chapter 03Lecture and

Animation Outline

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3.1 Cellular Organization

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A. Introduction

1. Three main parts of a cella. Plasma membrane – surrounds the

cell, keeps it intact, and regulates passage into and out of the cell

b. Nucleus – control centerc. Cytoplasm – gelatinous, semi-fluid of

water and suspended and dissolved substances

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Introduction, cont

2. Organelles (little organs) are scattered throughout the cytoplasm and have various functions

3. The cytoskeleton maintains cell shape and allows the cell and its content to move

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A typical animal cell

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B. Plasma Membrane

1. Separates the inside of the cell (cytoplasm) from the outside

2. Fluid-mosaic modela. Phospholipid bilayer – hydrophilic heads point

outward and hydrophobic tails point inwardb. Attached peripheral and integral proteins serve

as receptors, channels, and carriersc. Cholesterol molecules stabilize the membraned. Glycoproteins and glycolipids attached to outer

surface of some protein and lipid molecules, mark cells as belonging to a particular individual

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Fluid-mosaic model of the plasma membrane

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C. The Nucleus

1. Stores genetic information2. Chromatin

a. Contains DNA, protein, and some RNAb. Coils into rod-like structures called

chromosomes before the cell dividesc. Immersed in nucleoplasm

3. Nucleoli a. Dark-staining bodies containing rRNA

and proteinb. Site where ribosomes are formed

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The Nucleus, cont

4. Nuclear envelope separates nucleus from cytoplasm

a. Lipid bilayer with many nuclear poresb. Outer layer is continuous with the

endoplasmic reticulum

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The Nucleus

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D. Ribosomes

1. Composed of two subunits containing protein and rRNA

2. Can be found free within the cytoplasm, singly or in groups called polyribosomes; produce proteins that are used inside the cell

3. Also found attached to the endoplasmic reticulum; produce proteins that may be secreted by the cell

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E. Endomembrane System

1. Nuclear envelope2. Endoplasmic reticulum (ER)

a. Continuous with the outer membrane of the nuclear envelope, it is a system of membranous channels and saccules

b. Rough ER1) Has attached ribosomes2) Processes proteins produced by

attached ribosomes

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Endomembrane system, cont

c. Smooth ER 1) Has no attached ribosomes2) Synthesizes phospholipids, detoxifies

drugs, and has other functions depending on the type of cell

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Endoplasmic Reticulum

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Endomembrane System, cont

3. Golgi apparatusa. Stacks of curved sacculesb. Processes, packages, and secretes

various substancesc. Receives protein and/or lipid-filled

vesicles from ERd. Contains enzymes that modify proteins

and lipidse. Vesicles leave the Golgi apparatus and

move to other parts of the cell or to the plasma membrane for secretion

f. Produces lysosomes

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Endomembrane System Function

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Endomembrane system, cont

4. Lysosomesa. Contain hydrolytic digestive enzymes;

nick-names “suicide sacs”b. Autodigestion responsible for cell

rejuvenation and development and removal of worn-out organelles

c. Can fuse with vesicles of material brought into the cell for destruction

d. Tay-Sach’s disease – metabolic disorder involving missing or inactive lysosomal enzymes in nerve cells

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F. Peroxisomes and Vacuoles

1. Peroxisomesa. Enzyme-containing vesicles, similar to

lysosomesb. Detoxify drugs, alcohol, and other

toxinsc. Large numbers found in liver and

kidneyd. Break down fatty acids from fats

2. Vacuoles isolate substances captured inside the cell

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G. Mitochondria

1. Rod-shaped organelle bound by a double membrane

2. Inner membrane folds into cristae to increase surface area

3. Site of ATP production through cellular respiration – cell powerhouse

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Mitochondrion Structure

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1. The cytoskeleton

1. Microtubules - help maintain the cell’s shape and anchors or assists the movement of organelles

2. Intermediate filaments – involved in cell to cell junctions

3. Actin filaments – involved in cell movement4. Assembly regulated by the centrosome

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I. Centrioles

1. Composed of microtubules with a 9 + 0 pattern

2. A pair of perpendicular centrioles are found near the nucleus of every cell

3. In a area called the centrosome4. Involved in cell division by forming the

mitotic spindle5. Form the basal body (anchor point) for

each cilium or flagellum

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Structure of basal bodies and flagella

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1. Cilia and flagellum

1. Cilia are hair-like projections from the free surface of a cell; beat in unison to move material along the cell surface

2. Flagellum – a single whip-like extension for cell movement; sperm is the only human cell with a flagellum

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Cilia and flagella

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Structures in Human Cells

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3.2 Crossing the Plasma Membrane

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1. Introduction

1. The plasma membrane is selectively (semi) permeable – only certain ions and molecules can cross through

2. Passive processes – does NOT require cellular energy (ATP)

3. Active processes – DOES require cellular energy

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B. Simple Diffusion

1. Movement of atoms or molecules from an area of higher concentration to an area of lower concentration (down a concentration gradient)

2. Movement of atoms or molecules occur until they are equally distributed

3. No cellular energy is required (passive)4. Small lipid-soluble molecules will diffuse

through the lipid portion of the membrane; includes blood gases

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Diffusion

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C. Osmosis

1. Diffusion of water across a plasma membrane

2. Occurs when there is an unequal distribution of water on either side of a selectively permeable membrane; water passes freely but solutes do not

3. Osmotic pressure – force exerted on a selectively permeable membrane

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Osmosis, cont

4. Tonicity – concentration of solute versus the concentration of water

a. Isotonic – equal concentration of solutes (dissolved substances) and solvent (water) inside and outside cell; cell shape is maintained

b. Hypotonic – higher concentration of water (lower concentration of solutes) outside cell; water moves into cell causing it to swell and eventually lyse

c. Hypertonic – lower concentration of water (higher concentration of solutes) outside cell; water moves out of cell causing it to shrink or crenate

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Tonicity

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D. Filtration

1. Filtration is the movement of liquid from high pressure to low pressure

2. Blood pressure creates the hydrostatic pressure in capillaries where filtration occurs

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1. Transport by carriers

1. Facilitated diffusiona. Solutes are transported by means of a

protein carrierb. Movement from area of higher

concentration to area of lower concentration

c. No energy required - passive

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Transport by carriers, cont

2. Active transporta. Solutes move up their concentration

gradient (low concentration area to high concentration area)

b. Requires a protein carrier (often called pumps)

c. Requires the use of cellular energyd. The sodium/potassium pump (Na+/K+

pump) is an important pump that all cells have

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Active Transport

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F. Endocytosis and Exocytosis

1. In endocytosis (bring into the cell) the plasma membrane envelopes a substance and forms an intracellular vesicle

a. Phagocytosis (“cell eating”) – cell ingests solid particles

b. Pinocytosis (“cell drinking”) – cell consumes solutions

2. In exocytosis (takes out of the cell) a vesicle fuses with the plasma membrane as secretion occurs

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Crossing the Plasma Membrane

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3.3 The Cell Cycle

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A. Introduction

1. Set of stages that take place between the time a cell divides and the time the daughter cell divides

2. Controlled by external and internal signals3. Apoptosis (cell death) occurs at a

restriction checkpoint if the cell did not complete mitosis and is abnormal

4. Some specialized cells no longer go through the cell cycle - muscle cells and nerve cells

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B. Cell Cycle Stages - Interphase

1. Cell is not dividing, but is preparing to divide

2. The cell carries on regular activities3. Three phases

a. G1 phase – cell doubles number of organelles and accumulates materials used for DNA synthesis

b. S phase – “synthesis” phase; DNA replication occurs

c. G2 phase – cell synthesizes proteins that will assist cell division and completes replication of centrioles

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The Cell Cycle

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C. Major events during interphase

1. Replication of DNA

a. Before replication, the two strands of DNA are hydrogen bonded together

b. Parental DNA strands unwind (hydrogen bonds are broken)

c. New complimentary nucleotides pair with nucleotides in the parental DNA strands and DNA polymerase joins the new nucleotides

d. When replication is complete, two identical double helix molecules have been formed

e. Each strand of this double helix is equivalent to a chromatid; held together by the centromere

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Overview of DNA Replication

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Ladder configuration & DNA replication

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2. Protein synthesis

a. DNA also serves as a template for RNA formation and protein construction

b. Two steps involved in protein synthesis are:1) Transcription – formation of mRNA2) Translation – involves mRNA, tRNA,

and rRNA; specifies the order of amino acids in a polypeptide

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Protein Synthesis Process

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D. The Cell Cycle – Mitotic Stage

1. M-stage – nuclear division stage divided into 4 phasesa. Prophase

1) The centrioles near nucleus begin moving towards opposite ends of nucleus

2) Spindle fibers appear between the centrioles3) Nuclear envelope begins to fragment4) Nucleolus begins to disappear5) Chromosomes appear randomly and attached

to spindle fibers by their centromere

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M-stage, cont

b. Metaphase1) Spindle is fully formed2) Chromosomes are aligned at the equator

c. Anaphase1) Centromere splits2) Sister chromatids separate (now called

chromosomes)3) Chromosomes move toward opposite

poles of the spindle (toward centrioles)4) Some spindle fibers push the

chromosomes apart while others pull them toward the poles

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M-stage, cont

d. Telophase1) Chromosomes become chromatin 2) Spindle disappears and nucleoli appear3) Nuclear envelope reassembles and two

daughter cell nuclei can be observed

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1. The Cell Cycle - Cytokinesis

a. Cytokinesis – division of the cytoplasm and organelles

b. Begins in anaphase and completes in telophase

c. Actin filaments form a ring around the equator that contracts, pinching the cell in half

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Mitotic Stage of the Cell Cycle

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Mitosis in a whitefish embryo

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3. Importance of mitosis

a. Maintains chromosome numberb. Each cell in our body is genetically

identicalc. Each cell type has certain genes

turned on and others turned off to give the different types of body cells

d. Important to the growth and repair of multicellular organisms

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1. Meiosis

1. Known as reduction division because the chromosome number is cut in half

2. The four phase of mitosis are repeated twice with some changes in the steps that occur

3. The gametes (ova and sperm) have half the chromosomes of normal body cells so that when they join to form the zygote, the chromosome number is correct for that organism.