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Cell Structure & Function

Cell Theory

• All living things are made up of cells.

• Cells are the smallest working units of all living things.

• All cells come from preexisting cells through cell division.

Definition of Cell

A cell is the smallest unit that is capable of performing life

functions.

Cell Classified to function

1. Muscle cell2. Nerve cell3. Epithelial cell4. Connective tissue cell

Examples of Cells

Amoeba Proteus

Plant Stem

Red Blood Cell

Nerve Cell

Bacteria

Two Types of Cells

•Prokaryotic

•Eukaryotic

Prokaryotic

• Do not have structures surrounded by membranes

• Few internal structures

• One-celled organisms, Bacteria

Eukaryotic• Contain organelles (little organs) surrounded by

membranes• Most living organisms

Plant Animal

“Typical” Animal Cell

• Cells are surrounded by cell membrane

• The interior of the cell is divided:1. Nucleus

2. Cytoplasm

The Cytoplasm contains two components

1. Cell organelles

2. Cytosol

Cell Parts

Surrounding the Cell

Cell Membrane

Function of cell membrane

1. Regulate the passage of substance into and out of cell and between cell organelles and cytosol.

2. Link adjacent cells together3. Detect chemical

messengers arriving at the cell surface

The Cell Membrane Structure

Overview• Cell membrane separates living cell from

nonliving surroundings– thin barrier = 8nm thick

• Made of phospholipids, proteins & other macromolecules

Phospholipids

Fatty acid

Phosphate

• Fatty acid tails– hydrophobic

• Phosphate group head – hydrophilic

• Arranged as a bilayer

Phospholipid bilayer

polarhydrophilic

heads

nonpolarhydrophobic

tails

polarhydrophilic

heads

More than lipids… • In 1972, S.J. Singer & G. Nicolson proposed that membrane

proteins are inserted into the phospholipid bilayer• Two types of membrane protein1. Integral membrane2. Peripheral membrane

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of

the lipid bilayerExtracellular fluid

Cholesterol

Cytoplasm

Glycolipid

Transmembraneproteins

Filaments ofcytoskeleton

Peripheralprotein

Glycoprotein

Phospholipids

Membrane Proteins• Proteins determine membrane’s specific functions

– cell membrane & organelle membranes each have unique collections of proteins

• Membrane proteins:– peripheral proteins

• loosely bound to surface of membrane

– integral proteins • penetrate lipid bilayer, usually across whole membrane

• transmembrane protein

Proteins domains anchor molecule

• Within membrane– nonpolar amino acids

• hydrophobic • anchors protein

into membrane

• On outer surfaces of membrane– polar amino acids

• hydrophilic• extend into extracellular

fluid & into cytosol

Polar areasof protein

Nonpolar areas of protein

Many Functions of Membrane ProteinsOutside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion

Membrane carbohydrates • Play a key role in cell-cell recognition

– ability of a cell to distinguish one cell from another

– important in organ & tissue development

Membrane Junctions

• Some cell not anchored to other cells but suspend in the fluid.

• Most cells are packaged into tissues and are not free to move.

• Many cells physically joined by specialized types:

1. Desmosomes2. Tight junctions3. Gap junctions

Inside the Cell

Nucleus

• Almost all cells contain a single nucleus.• Directs cell activities• Separated from cytoplasm by nuclear membrane• Function-Stores and transmits genetic information in the

form of DNA. Genetic information passes from the nucleus to the cytoplasm

Nuclear Membrane

• Surrounds nucleus• Made of two layers

Nuclear envelope

Nuclear pores• Openings allow

material to enter and leave nucleus

http://library.thinkquest.org/12413/structures.html

Chromosomes

• In nucleus• Made of DNA• Contain instructions

for traits & characteristics


Nucleolus

• Inside nucleus• Contains RNA to build

proteins


Endoplasmic Reticulum• Moves materials around

in cell• Smooth type (Agranular):

lacks ribosomes. Site of lipid molecule synthesized

• Rough type (Granular): ribosomes embedded in surface. Packaging of proteins to be secreted or distributed.


Ribosomes

• Composed of proteins and several RNA molecules

• Proteins factories of the cell

• Either bound to the organelle or found free in the cytoplasm


Golgi Apparatus

• Most cells have single Golgi apparatus.

• Protein 'packaging plant'

• Move materials within the cell

• Move materials out of the cell


Lysosome• Spherical or oval• Typical cell may contain

several hundreds• Digestive enzyme for

proteins, fats, and carbohydrates

• Transports undigested material to cell membrane for removal

• Cell breaks down if lysosome explodes


Mitochondria

• Spherical rode like structure• Produces energy through

chemical reactions – breaking down fats & carbohydrates

• Controls level of water and other materials in cell

• Recycles and decomposes proteins, fats, and carbohydrates
