chapter 3 cell structure and function. eukaryotic cell structure
TRANSCRIPT
Chapter 3Cell Structure and Function
Eukaryotic Cell Structure
Chemical Components of Cells
• Most cells are composed of 4 elements– Carbon– Hydrogen– Oxygen– Nitrogen
• Cells are about 60% water
Anatomy of a Generalized Cell
• Cells have 4 main regions (parts)– Nucleus– Cytoplasm– Plasma Membrane
Nucleus
• Control center• Cell reproduction
DNA --Visible Chromosomes• Nuclear envelope
– Double membrane– Pores
• Nucleoli– rRNA and tRNA assembly
Cell Membrane-fluid mosaic
• Controls movement into and out of the cell
• Composed of – lipid and protein bilayer– Cholesterol– Glycolipids– Glycoproteins
Components of Cell Membrane(Fluid Mosaic Model)
• Phospholipids (bilayer)– Phospholipids
• Hydrophillic (water loving) Head: Phosphate and glycerol• Hydrophobic Tails (water hating): impermeable to most
water soluble molelcules• Cholesterol – membrane fluidity
• Proteins: Receptors, enzymes, transport channels or carriers
• Receptors: Glycoproteins and Glycolipids– Blood type, organ transplant rejection
ORGANELLES
• Specialized cellular compartments• Many membrane bound
Cytoplasm (Cytosol)
• Semi-fluid material suspends other elements
• Contains enzymes
Mitochondrion
• Double membrane– Internal folds
• Cellular Respiration!!! Energy for cell
• Contains its own DNA and RNA
Ribosomes
• Site of Protein synthesis• Found
– free in cytoplasm– As a part of the Rough ER
Endoplasmic Reticulum
• Fluid Filled Tubules • Rough ER
– Contains Ribosomes– Moves proteins within cell
• Smooth ER– No Ribosomes– Protein modification– Lipid metabolism
Rough ER
Golgi Apparatus
• Flattened sacs • Modifies, Sorts, and
packages proteins arriving from ER for delivery
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Golgi Animation
Materials are transported from Rough ER to Golgi to the cell membrane by
VESICLES
3 types of packages
Lysosomes• Intracellular digestion
(enzymes)• Membranous “bags” from
golgi apparatus • Fuse with vesicles
– Ingested food – Damaged organelles
Tay-Sachs disease-missing or inactive lysosomal enzymes
Cytoskeleton
• Protein network made of…– Microfilaments– intermediate filaments– Microtubules
• Cell Shape• Internal Organization• Organelle Movement!
Figure 3.7 Cytoskeletal elements support the cell and help to generate movement.
Actin subunit
7 nm
Fibrous subunitsTubulin subunits
10 nm 25 nm
Microfilaments form the bluebatlike network.
(a) Microfilaments (b) Intermediate filaments (c) Microtubules
Intermediate filaments formthe purple networksurrounding the pink nucleus.
Microtubules appear as goldnetworks surrounding thecells’ pink nuclei.
Centrioles
• Rod shaped made of Microtubules
• Before mitosis-pairs duplicate + separate– Produces Mitotic Spindles
Cilia and Flagella
• Cell movement – Sperm cells-flagella
• Movement of materials along surface– Respiratory tract-cilia
• Microvilli – fingerlike extensions – Increase surface area for absorption
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Cilia Moving Away Dust Particles from the Lungs
Respiratory System
Membrane Transport
• Two basic methods– Passive Transport (no energy required)– Active Transport (energy required ATP)
Passive Transport
• Diffusion – Simple: lipid soluble or
small– Osmosis: water moves
thru
aquaporins– Facilitated: use carriers– Filtration
Passive Transport: Filtration
• Water and solutes are forced through a membrane because of a pressure gradient
• Through capillary walls– Movement of water or small solutes– Kidneys-blood filtration
Active Transport• Solute pumping• Requires protein carriers• ATP used
Examples: sodium/potassium pump
Active Transport
• Endocytosis: into the cell– Phagocytosis: engulfing large particles– Pinocytosis: cell drinking
• Exocytosis: movement out of the cell
Figure 3.12b Exocytosis.
(b) Electron micrograph of asecretory vesicle inexocytosis (190,000×)
Figure 3.13b Events and types of endocytosis.
Pseudopod
Bacteriumor otherparticle
Extracellularfluid
Cytoplasm
(b)
Figure 3.13a Events and types of endocytosis.
PlasmamembraneLysosome
Pit
Ingestedsubstance
Detached vesicle
Vesicle
Extracellularfluid Cytosol
Release ofcontents tocytosol
Vesicle fusingwith lysosomefor digestion
Transport to plasmamembrane and exocytosisof vesicle contents
Membranes and receptors(if present) recycled to plasmamembrane
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(a)
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3
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Cell Life Cycle
• INTERPHASE– Cell growth– Carries on regular cell activities
• CELL DIVISION– Cell replicates itself to produce more cells for
growth and repair
Interphase
• G1: “growth” – protein synthesis, organelles double
• S: “synthesis” phase– DNA replication/duplicated chromosomes
• G2: – Protein synthesis, chromatin condenses,
chromosomes visible, final preparation to divide
Cell Division
• Mitosis – division of the nucleus– Result: 2 daughter nuclei
• Cytokinesis – division of the cytoplasm– Result: 2 daughter cells
Spindlemicrotubules
Chromosome,consisting of twosister chromatids
Fragments ofnuclear envelope
Daughterchromosomes
Figure 3.15 Stages of mitosis.
Centrioles Chromatin Centrioles
Formingmitoticspindle
Centromere
Centromere
Plasmamembrane
NuclearenvelopeNucleolus
Spindlepole
Metaphaseplate
Nucleolusforming
Cleavagefurrow
Spindle Sisterchromatids
Nuclearenvelopeforming
Interphase Early prophase Late prophase
Metaphase Anaphase Telophase and cytokinesis
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Cytokinesis
• Division of cytoplasm• Cell pinched into 2
daughter cells
Protein Synthesis
(into) (into)
DNA mRNA Protein
transcription translation
As the ribosomemoves along the mRNA,a new amino acid isadded to the growingprotein chain.
Released tRNAreenters thecytoplasmic pool,ready to be rechargedwith a new aminoacid.
mRNA specifying onepolypeptide is made onDNA template.
mRNA leavesnucleus and attachesto ribosome, andtranslation begins.
Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via its anticodonto the codon.
mRNA
Figure 3.16 Protein synthesis.
Nuclear membrane
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1
3
4
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Nuclear pore
Nucleus(site of transcription)
DNA
Aminoacids
Cytoplasm(site of translation)
Synthetaseenzyme
Correct aminoacid attached toeach species oftRNA by an enzyme
Growingpolypeptidechain
Peptide bond
tRNA “head”bearing anticodon
Large ribosomal subunit
Codon
Portion ofmRNA alreadytranslated
Small ribosomal subunit
Direction ofribosome advance;ribosome moves themRNA strand alongsequentially as each codon is read.
Met
Gly
Ser
Phe
Ala
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