Cell Structure and FunctionChapter 4

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What is a Cell?• The smallest unit of matter

that can carry all processes of life.

• Structure directly related to Function

• ≈ 10-100 trillion cell in the human body

• All cells are not created equal• cell diversity-cells differ

in shape, size, and organization• Limited in size by surface

area to volume ratio• Shape indicates function

• At least 200 cell types in your body!

www.tutorvista.com/.../structure-cell.php

Background CheckCell Discovery:

◦ Possible by development of microscope

◦ Robert Hooke-examined cork

◦ Anton van Leeuwenhoek-1st to observe living cells

• Cell Theory:1. All living things are

composed of one or more cells

2. Cells are the basic units of structure and function in an organism

3. Cells come only from the reproduction of existing cells

www.microbeworld.org/index.php?option=com_con...

askabiologist.asu.edu/.../rhooke.html

Eukaryotes Vs. ProkaryotesEukaryotes:

◦ Membrane-bound nucleus and organelles

◦ Example(s): YOU, animals, plants, fungi, protists

Prokaryotes:◦ Lack nucleus and

membrane-bound organelles

◦ Example(s): bacteria

www.uoregon.edu/~bsl/astronomy/

Cell Membrane

Surrounds entire cell Selectively

permeable – some substances pass with ease while others cannot pass at all

Made of:-- Lipids and proteins

Fluid Mosaic Model

commons.wikimedia.org/wiki/File:Cell_membrane...

Membrane Lipids and ProteinsPhospholipids

◦ Polar head: hydrophilic

◦ Nonpolar tails: hydrophobic

◦ Forms lipid bilayer

Steroids◦ Cholesterol main

steroid in animal cells

◦ Stabilize membrane/maintain fluidity

Proteins◦ Peripheral proteins: on

exterior or interior surface of cell membrane

◦ Integral proteins: embedded in lipid bilayer Carbohydrates:

involved with self recognition and attachment

Transport of molecules through bilayer (channels or pores)

Cytoplasm/CytosolCytoplasm:

◦ Area between cell membrane and nucleus contains organelles

• Cytosol: Gelatin-like

aqueous in cytoplasm

Salts, minerals, organic molecules

Mitochondria

Site of chemical reactions producing ATP – “power house”

Own DNA and grow and divide on own

2 membranes◦ Smooth outer:

boundary◦ Inner: cristae

(folds)- enlarge surface area for reactions

www.yellowtang.org/cells.php

RibosomesNo membraneTwo compounds-

proteins and RNAAssembled in

nucleusFree or attached to

Endoplasmic reticulum

Role: protein synthesis

www.biologie.uni-hamburg.de/b-online/library/...

Endoplasmic Reticulum (ER)

System of membranous tubules and sacs

Function: intracellular highway

2 types:◦ Rough- has ribosomes

cells with high rate of proteins being exported out or inserted into membrane

◦ Smooth- no ribosomes calcium regulation in

muscle cells Breaks down toxic materials

www.yellowtang.org/cells.php

Golgi ApparatusThe UPS of the cell

◦ Packaging, processing, and secreting proteins

System of membranes/sacs◦ Works closely with ER

www.yellowtang.org/cells.php

LysosomesSmall and spherical

◦ Enclose hydrolytic enzymes

Enzyme use:◦ Digest- proteins,

carbohydrates, lipids, RNA, DNA

◦ Digest- old organelles, viruses, and bacteria

Common in: ◦ Animals, fungi, and

protists ◦ RARE in plants

CytoskeletonLong protein strands in

cytosol ◦ maintain cell shape and size◦ support and movement◦ No membrane

2 Components:◦ Microfilaments-

Actin polymer chains Smallest Contribute to movement and

contraction of muscle

◦ Microtubules- hollow tubes Largest Active role in cell division-

spindle fibers

Cilia and FlagellaCilia

◦ Hair-like organelles ◦ Numerous on cell ◦ Crawling motion

Help unicellular bacteria search for food/escape

On surface of respiratory tract

Flagella◦ Hair-like organelles◦ Long, less

numerous◦ Swimming/

whipping motion Quick movement for

unicellular organisms

Nucleus- “the brain”Nuclear matrix

◦ Protein skeleton◦ Maintains shape

Nuclear envelope◦ Double membrane◦ Chromatin within

DNA and protein combination Coil for cell division forming

chromosomes

Nuclear Pores-visible◦ Holes in envelope

Nucleolus-visible◦ Ribosome

synthesis/partially assembled

www.cartage.org.lb/.../Nucleus/Nucleus.htm

Cell Wall- Plant cellsOutside cell membraneRigid- support and

protection◦ Long chains of cellulose◦ Pores-allow passage of

ions and molecules2 types

◦ Primary- when cell being formed

◦ Secondary- when cell reaches full size Between primary wall and

membrane Tough and woody

www.microscopy-uk.org.uk/.../fixation.html

Vacuoles- Plant cellsFluid-filledOften large can

occupy up to 90% of cell volume

Storage:◦ Store enzymes and

metabolic waste◦ Some waste toxic-

can be a defense

www.yellowtang.org/cells.php

Plastids- Plant cellsDouble membrane and contains DNAStore:

◦ Starch, fats, or pigmentsChloroplast- most common

◦ Chlorophyll- green pigment◦ Thylakoids: system of flattened, membranous sacs

Sunlight converted to chemical energy- PhotosynthesisOther plastids contian pigments that give fruit

and flowers color

www.yellowtang.org/cells.php