a tour of the cell - mission...

Reference: Chapter 2

A Tour of the Cell reference: Chapter 6

1

Monkey Fibroblast Cells stained with fluorescent dyes to show the nucleus

(blue) and cytoskeleton (yellow and red fibers), image courtesy of Nikon

Instruments & Florida State University

Overview & Objectives

v Outline §  Basic Features of Cells §  Animal Cell Structures

v Objectives §  List the major structures that make up animal cells and describe

their functions §  Be able to recognize and label organelles and other cell structures

in a picture of a cell

v Important concepts: §  Cells are the building blocks of all life §  Cells are the smallest living things §  Cells arise only from other cells

Cells

v Living organisms are either §  Prokaryotes

§  Single-celled organisms that lack specialized internal structures, such as a nucleus

§  e.g. bacteria

§  Eukaryotes §  Organisms whose cells contains a nucleus

and other complex internal structures

§  May be single-celled (e.g. protozoa such as amoebae

§  Multi-celled, such as plants and animals (and you!)

THE MICROSCOPIC WORLD OF CELLS v  Scale:

§  mm = millimeter = one thousandth of a meter (small; barely see it) §  µm = micrometer = one millionth of a meter (really small; can’t see it)

§  nm = nanometer = one billionth of a meter (really, really really small)

Cell Structures

v All cells consist of two basic components: §  Plasma Membrane (aka Cell Membrane)

§  This encloses the contents of the cell and regulates the passage of materials into and out of the cell

§  Cytoplasm §  Internal contents of the cell

v Many cells also possess an Extracellular Matrix §  Material that forms a coating around the cell §  Holds cells together in tissues; can also be the starting material for

bone and other structures

Cell Structures: The Plasma Membrane

v Separates the living cell (cytoplasm) from its nonliving surroundings

v The membranes of cells are composed of macromolecules §  Lipids §  Proteins §  Carbohydrate

Cell Structures: The Plasma Membrane

v The lipids belong to a special category called phospholipids §  Glycerol backbone §  Two hydrophobic fatty

acid “tails” §  Hydrophilic phosphate

“head” §  Organic group (R)

sometimes attached to phosphate § proteins §  carbohydrates

Cell Structures: The Plasma Membrane

v Phospholipids form a two-layered membrane, the phospholipid bilayer

v This thin, flexible bilayer surrounds the cell contents and prevents most materials from entering or leaving the cell

Outside cell

Cytoplasm (inside cell)

(a) Phospholipid bilayer of membrane

Cell Structures: The Plasma Membrane v Carbohydrate chains attach to the proteins and lipids in

the plasma membrane §  Important in cell-cell recognition

Cell Structures: The Cytoplasm

v  A semi-fluid matrix that fills the interior of the cell v  Most cellular activities occur in the cytoplasm

§  Highly organized §  Consists of 3 components

1.   Cytosol §  Gooey liquid; makes up about 80% of the cell §  Composed of water, salts, organic molecules

2.   Organelles §  “Little organs”; specialized structures in the

cytoplasm 3.   Vesicles

§  Membrane-bound sacks that transport materials and carry out chemical reactions within the cell

Cell Organelles: The Nucleus v The nucleus is the “manager” of the cell

§  Contains chromatin (DNA) that carries the genes which code for proteins

§  Bordered by a double membrane called the nuclear envelope

§  Also contains the nucleolus, a region of the nucleus where ribosomes are assembled

Cell Organelles: Ribosomes

v  Ribosomes are small organelles §  Mixture of protein and RNA (ribonucleic acid) §  synthesize the cell’s proteins

Cell Organelles: The Endomembrane System

v  Many of the membranous organelles in the cell belong to the endomembrane system §  They manufacture and

distribute cell products

v  Four components: 1.   Rough Endoplasmic

Reticulum (RER) 2.   Smooth Endoplasmic

Reticulum (SER) 3.   Golgi Apparatus 4.   Lysosomes

The Endoplasmic Reticulum

v The endoplasmic reticulum (ER)

§  Produces an enormous variety of molecules

§  Is composed of smooth and rough ER

Nuclear envelope

Ribosomes

Rough ER Smooth ER

1. Rough Endoplasmic Reticulum, RER

v “Roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane

v The functions of the RER include: §  Producing proteins §  Producing new membrane

RER

1. Rough Endoplasmic Reticulum, RER

v After the rough ER synthesizes a molecule it packages the molecule into transport vesicles

Transport vesicle buds off

Ribosome Secretory protein inside transport vesicle

Protein Rough ER

Polypeptide

1 2

3

4

2. Smooth Endoplasmic Reticulum, SER

v SER lacks the surface ribosomes of RER §  Produces a different

variety of compounds, such as lipids, including steroids

SER

3. The Golgi Apparatus

v Golgi works in partnership with the ER §  Refines, stores, and distributes the products of cells

§  The “UPS Store” of the cell §  Consists of flattened membranous “sacks” §  Vesicles fuse and pinch off from the sacks

Transport vesicle from ER

“Receiving” side of Golgi apparatus

Golgi apparatus

New vesicle forming

Transport vesicle from the Golgi

“Shipping” side of Golgi apparatus

Plasma membrane

4. Lysosomes

v  A lysosome is a membrane-enclosed sack §  contains digestive enzymes §  Lysosomes have 2 functions:

1.  fuse with food vacuoles to digest food

4. Lysosomes

2.  break down damaged organelles

•  Visual Summary: The Endomembrane System

Cell Organelles: Mitochondria

v Cells require a constant energy supply to carry out the work of life

v Cells use a chemical form of energy known as ATP (adenosine triphosphate)

v Mitochondria are “Powerplants” that supply the cell’s energy needs by producing ATP

v Production of ATP is known as Cellular Respiration

mitochondria

Cell Structures: The Cytoskeleton

v The cytoskeleton is the infrastructure of the cell v Consists of a network of protein fibers v Controls cell shape and movement

Flagella and Cilia

v Cilia and flagella are external appendages

v Flagella propel the cell in a whiplike motion

§  Useful when you need to get somewhere in a hurry, like the sperm cell shown below

Flagella and Cilia

v Cilia are smaller than flagella §  Usually occur rows along the surface of the cell §  Beat in a coordinated fashion for locomotion or to move particles

toward or away from the cell

v The ciliates are a group of single-celled protists that have cilia covering the entire body

v Small animals like rotifers use cilia to gather food

Flagella and Cilia

v More structurally complex animals often have ciliated cells within their bodies

v The human windpipe is lined with cilia, as is the lining of the female reproductive tract

v  In the windpipe, the cilia beat in unison to propel dust and mucus out of the lungs

A Panoramic View of Eukaryotic Cells

Summary: Prokaryotic Cells Fimbriae

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella A typical

rod-shaped bacterium

(a)

Bacterial chromosome

0.5 µm

A thin section through the bacterium Bacillus

coagulans (TEM)

(b)

v Prokaryotic cells are characterized by having §  No nucleus §  DNA in an unbound region called the nucleoid §  No membrane-bound organelles §  Cytoplasm bound by the plasma membrane

Summary: Prokaryotic Cells

v Eukaryotic cells are characterized by having §  DNA in a nucleus that is bounded by a membranous

nuclear envelope §  Membrane-bound organelles §  Cytoplasm in the region between the plasma

membrane and nucleus

v Eukaryotic cells are generally much larger than prokaryotic cells

Summary: Eukaryotic Cells

Summary: Eukaryotic Cells

(Animal) Flagellum

Centrosome

CYTOSKELETON: Microfilaments

Intermediate filaments Microtubules

Microvilli

Peroxisome

Mitochondrion Lysosome

Golgi apparatus

Ribosomes

Plasma membrane

Nuclear envelope

Nucleolus

Chromatin

NUCLEUS

ENDOPLASMIC RETICULUM (ER)

Rough ER Smooth ER

Plant cells are also Eukaryotic, but have a few unique features… NUCLEUS

Nuclear envelope

Nucleolus Chromatin Rough ER

Smooth ER

Ribosomes

Central vacuole Microfilaments Microtubules

CYTOSKELETON

Chloroplast

Plasmodesmata Wall of adjacent cell

Cell wall

Plasma membrane

Peroxisome Mitochondrion

Golgi apparatus