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Chapter 3 Cells: The Living Units

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Page 1: Ppt chapter 031

Chapter 3

Cells: The Living Units

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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cell Theory

• The cell is the basic structural and functional unit of life

• Organisms depend on individual and collective activity of cells, dictated by subcellular structures

• Continuity of life has a cellular basis

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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structure of a Generalized Cell

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Plasma Membrane

• Separates intracellular fluids from extracellular fluids

• Plays a dynamic role in cellular activity

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Fluid Mosaic Model

• Double bilayer of lipids with imbedded, dispersed proteins

• Bilayer consists of phospholipids, glycolipids, cholesterol and proteins

• Phospholipid bilayer has hydrophobic (in the middle) and hydrophilic (facing the outside) portions

• Glycolipids are lipids with bound carbohydrates

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Fluid Mosaic Model of Plasma Membrane

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Functions of Membrane Integral Proteins

• Transport –channels or transporters

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Functions of Membrane Peripheral Proteins

• Attach to inner cytoplasm

• Part of glycocalyx outer coating as:

• Receptors

• Enzymes

• Cell identification markers

• Intercellular linkers

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Cell Environment Interactions

• Membrane receptors used for:

• Contact signaling – cell recognition

• Electrical signaling – voltage-regulated “ion gates” in nerve and muscle tissue

• Chemical signaling – neurotransmitters and hormones

• Cell linkers anchor cells, assist in movement of cells past one another, send signals for repair and immunity

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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Membrane Potential

• Voltage across a membrane

• Resting membrane potential

• Ranges from –20 to –200 mV

• Results from Na+ and K+ concentration gradients across the membrane

• Differential permeability of the plasma membrane to Na+ and K+

Figure 3.13

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Membrane Transport• The cell membrane is selectively permeable to

substances in the interstitial (extracellular) fluid

• Passive transport processes require no energy

• Active transport processes require energy

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Diffusion

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Passive Membrane Transport: Diffusion

• Simple diffusion –movement from higher to lower concentration

• Nonpolar, lipid-soluble substances diffuse directly through the cell lipid bilayer

• Most small polar substances must go through integral protein channels

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Passive Membrane Transport: Facilitated Diffusion

• Large polar molecules (sugars) combine with integral protein transporters that aid transport across membrane

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Passive Membrane Transport: Osmosis

• Diffusion of water across a semipermeable membrane

• Occurs when the concentration of water is different on opposite sides of a selective, water permeable membrane

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Effect of Membrane Permeability on Osmosis

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Tonicity

• Isotonic – solution has the same solute concentration as that of the cell

• Hypotonic – solution has lesser solute concentration than that of the cell

• Hypertonic – solution has greater solute concentration than that of the cell

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Passive Membrane Transport: Filtration

• The passage of water and solutes through a membrane by pressure

• Pressure gradient pushes substances from a higher-pressure area to a lower-pressure area

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Active Transport (Solute Pump)

• Solutes move against a concentration gradient (uphill)

• Uses ATP to help move solutes across the membrane

• Requires integral transport proteins

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Types of Active Transport

• Symport system – two substances are moved across the membrane in the same direction

• Antiport system – two substances are moved across the membrane in opposite directions

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Types of Active Transport

• Primary active transport – phosphate from ATP causes conformational change of transport protein, which then transports substance

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Types of Active Transport

• Secondary active transport – as Na+ goes across membrane, other solutes (like glucose) “piggyback” across with it

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Vesicular Transport

• Transport of large particles (macromolecules) across plasma membranes

• Exocytosis – moves substance from the cell interior to the extracellular space

• Endocytosis – enables macromolecules to enter the cell

• Phagocytosis – engulf solids and bring them into the cell’s interior

• Pinocytosis – engulf liquids

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Vesicular Transport

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Cytoplasm

• Cytoplasm – material between plasma membrane and the nucleus; contains:

• Cytosol – Colloid of water with dissolved protein, salts, sugars and other solutes

• Inclusions – large chemical substances

• Cytoplasmic organelles – metabolic machinery of the cell

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Cytoplasmic Organelles

• Specialized cellular compartments with specialized functions – division of labor

• Most are membrane - bound

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Cytoskeleton

• The “skeleton” of the cell

• Consists of microfilaments, intermediate filaments and microtubules

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Microfilaments

• Smallest strands like a beaded necklace

• Function to change cell shape, cell movement, endocytosis, exocytosis and support microvilli

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Intermediate Filaments

• Tough, insoluble protein fibers constructed like rope

• Resist pulling forces in the cell

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Microtubules

• Hollow tubes made of a spherical protein

• Determine the overall shape of the cell and distribution of organelles

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Centrioles

• Small barrel-shaped organelles located near the nucleus

• Pinwheel array of microtubules

• Organize mitotic spindle during mitosis

• Form the bases of cilia and flagella

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Cilia

• Hairlike, motile cellular extensions on exposed surfaces of certain cells

• Move substances across cell surface

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Flagella

• “Tail” of sperm cells for cell movement

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Ribosomes

• Granules containing rRNA and protein

• Site of protein synthesis

• Free ribosomes synthesize soluble proteins

• Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

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Endoplasmic Reticulum (ER)

• Interconnected tubes and parallel membranes enclosing cisterna

• Two varieties – rough ER and smooth ER

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Rough Endoplasmic Reticulum

• External surface studded with ribosomes

• Manufactures and transports protein containing compounds for internal use, integral proteins of plasma membranes and ultimately secretion

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Smooth Endoplasmic Reticulum

• Function to synthesis and internal transport of lipid containing compounds

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Golgi Complex

• Stacked and flattened membranous sacs

• Functions in packaging compounds from the ER to make:

• Secretory vesicles for export from the cell, plasma membrane components or lysosomes

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Role of the Golgi Complex

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Lysosomes

• Spherical sacs containing digestive enzymes:

• Digest ingested bacteria, viruses or toxins

• Breakdown useless tissue

• Degrade nonfunctional organelles

• Cell suicide

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Peroxisomes

• Sacs that contain detoxifying enzymes to detoxify harmful substances, including free radicals – highly reactive chemicals that can damage cells

• Ex: liver & kidney

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Proteasomes

• Contain proteases, enzymes that cut or degrade faulty cellular proteins into small peptides

• 4 stacked rings around a central core

• Too small to see under a light microscope

• In both the cytosol & nucleus

• Malfunction can result in Alzheimer’s & Parkinson’s diseases

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Mitochondria

• Double membrane structure with inner membrane shelves called cristae and matrix between

• Function to provide the cell’s ATP via aerobic cellular respiration

• Contain their own DNA and RNA

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Nucleus

• Gene-containing control center of the cell contains the genetic library with blueprints for nearly all cellular proteins; dictates the kinds and amounts of proteins to be synthesized

• Contains nuclear envelope, nucleolus and chromatin

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Nucleus

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Nuclear Envelope

• Selectively permeable double membrane barrier containing pores

• Pore complex regulates transport of large molecules into and out of the nucleus

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Nucleolus

• Dark-staining spherical body within the nucleus

• Site of ribosome production

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Chromatin

• Threadlike strands of DNA

• Condense and form barlike bodies called chromosomes when the nucleus starts to divide

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Protein Synthesis

• DNA serves as master blueprint for protein synthesis

• Genes are segments of DNA carrying instructions for a polypeptide chain

• Triplets of nucleotide bases form the genetic library; each triplet specifies coding for an amino acid

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Transcription

• Occurs in the nucleus

• Transfer of information from the DNA strand to the mRNA as mRNA is synthesized

• Each DNA triplet codes for a corresponding 3-base sequence of RNA, called a codon

• Each codon corresponds to a DNA triplet

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Transcription

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Genetic Code

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Translation

• Involves all three types of RNA – mRNA, rRNA, and tRNA

• Occurs in the cytoplasm at the ribosomes; mRNA leaves the nucleus and goes to the ribosomes

• rRNA (part of ribosomes) is the anchoring site where mRNA is read and tRNA brings in the various amino acid to build a polypeptide

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Translation

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Roles of the Three Types of RNA

• Messenger RNA (mRNA) carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm

• Ribosomal RNA (rRNA) is a structural component of ribosomes and site of protein synthesis

• Transfer RNAs (tRNAs) bound to amino acids base pair their anticodons with the codons of mRNA at the ribosome to begin the process of protein synthesis

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Information Transfer from DNA to RNA to Make Proteins

• DNA triplets are transcribed into mRNA codons

• Codons base pair with tRNA anticodons at the ribosomes

• Amino acids are peptide bonded at the ribosomes to form polypeptide chains

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Information Transfer from DNA to RNA to Make Proteins

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Cell Life Cycle

• Interphase

• Growth (G1), synthesis (S), growth (G2)

• Cell division is essential for body growth and tissue repair

• Mitosis (nuclear division)

• Cytokinesis (cytoplasm division)

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Interphase Parts• G1 – normal metabolic activity and growth

• If cell gets signal to divide, then

• S (synthesis) – DNA (chromosomes) and centrioles replicate

• G2 – enzyme preparation for division

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DNA Replication

• The DNA double helix unwinds into two complementary nucleotide chains; hydrogen bonds between nucleotides break

• Freed nucleotide strands serve as templates for replication

• Complementary nucleotide strands form: A-T; G-C

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Mitosis Phases

• Prophase

• Metaphase

• Anaphase

• Telophase

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Prophase

• Chromatin condenses into chromosomes

• Nuclear envelope and nucleolus disappear

• Centriole pairs separate and the mitotic spindle forms

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Metaphase

• Chromosomes cluster at the middle of the cell with their centromeres aligned at the exact center, or equator, of the cell

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Anaphase

• Sister chromatids split

• Chromosomes are pulled toward poles

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Telophase and Cytokinesis• Chromosomes nearly reach poles

• New sets of chromosomes unwind into chromatin

• New nuclear membrane and nucleolus reappear

• Cytokinesis occurs at the same time

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Cytokinesis

• Cleavage furrow formed in late anaphase by a contractile ring

• Cytoplasm is pinched in two as mitosis ends

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Aging Theories

• Mitosis ceases

• Telemeres (tips of chromosomes) lost each mitosis

• Glucose bridges to proteins

• Free radical damage

• Autoimmunity