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)

2

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

2

1

3

4

5

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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