Chapter 6 Notes - Valenciafd.valenciacollege.edu/file/nwilliams46/Chapter 6 notes.pdf– They are enclosed by a plasma membrane ... -All cells have ribosomes, ... – Have their DNA

Chapter 6 Notes

A Tour Of the Cell

Microscopy

● Light Microscope (EM)

● - visible light is passed through the specimen and then

through glass lenses

● Electron Microscope (EM)

● -focuses a beam of electrons through the specimen or

onto its surface

● Scanning Electron Microscope (SEM)

● -useful for detailed study of the topography of a specimen

● Transmission Electron Microscope (TEM)

● -used to study the internal structure of cells

Cells

● Eukaryotic cells have internal membranes that

compartmentalize their functions

● Cells are the basic structural and functional units of

every organism

● There are two types of cells:

● -Prokaryotic cells: Domains Bacteria and Archaea

● -Eukaryotic cells: Protists, Fungi, Animals and

Plants

Comparing Prokaryotic and Eukaryotic Cells

• All cells have several basic features in common

– They are enclosed by a plasma membrane

• Functions as a selective barrier

• Allows sufficient passage of nutrients

and waste

-Inside all cells is a semifluid, jelly-like substance called

cytosol, in which subcellular components are

suspended

-All cells contain chromosomes, which carry genes in the

form of DNA

-All cells have ribosomes, tiny complexes that make

proteins according to instructions from the genes

• Prokaryotic cells

– Do not contain a nucleus

– Have their DNA located in a region called

the nucleiod

• Eukaryotic cells

–Contain a true nucleus, enclosed by a membranous

nuclear envelope

–Are generally quite a bit bigger than prokaryotic cells

A Panoramic View of the Eukaryotic Cell

• Eukaryotic cells

–Have extensive and elaborately arranged internal membranes,

which form organelles

– Larger than prokaryotic cells

– complex internal structure with membranous and

non-membranous organelles

• membranous: nucleus, endoplasmic reticulum, Golgi

apparatus,mitochondria, lysosomes and peroxisomes

• non-membranous: ribosomes, microtubules, centrioles,

flagella and cytoskeleton

Plant and animal cells have most of the same organelles

The Nucleus: Information Central

●The nucleus contains most of the genes in the

eukaryotic cell

●The nucleus houses chromosomes, which are made

of chromatin (DNA and proteins)

• The nuclear envelope

– Encloses the nucleus, separating its contents

from the cytoplasm

-Nuclear envelope is a double membrane

-also contains nucleoli, where ribosomal subunits

are made

Ribosomes: Protein Factories

• Ribosomes

–Are particles made of ribosomal RNA and protein

– Site of protein synthesis

● Build proteins in two cytoplasmic locales:

● -Free Ribosomes-suspended in the cytosol

● -Bound Ribosomes-attached to the outside of the

endoplasmic reticulum or nuclear envelope

● Bound and free ribosomes are structurally identical,

and ribosomes can alternate between two roles

Endomembrane System

• The endomembrane system regulates protein

traffic and performs metabolic functions in the cell

• The endomembrane system includes:

– Endoplasmic reticulum (ER)

– Golgi apparatus

– Lysosomes

– Vacuoles

– (plasma membrane)

Endoplasmic Reticulum: Biosynthetic Factory

•The ER membrane is continuous with the nuclear envelope

• There are two distinct regions of ER

-which lack ribosomes

-with attached ribosomes

Two regions of ER:

• The smooth ER-outer surface lacks ribosomes appears smooth

– Synthesizes lipids

– Metabolizes carbohydrates

– Stores calcium

– Detoxifies poison

• The rough ER-studded with ribosomes appears rough

– Aids in synthesis of secretory and other proteins to make glycoproteins; produces new

membrane

Golgi Apparatus: Shipping and Receiving Center

• After leaving the ER, many transport vesicles travel to the Golgi

Apparatus

The Golgi apparatus

• Golgi apparatus finishes, sorts and ships cell

products transported in vesicles from ER

– consists of flattened membranous sacs called cisternae

–Receives many of the transport vesicles produced in the rough

ER

- Modifies some of the products of the rough ER

-Synthesis of many polysaccharides

Lysosomes: Digestive Compartments

• A lysosome

– Is a membranous sac of hydrolytic enzymes

● Lysosomes contain enzymes to digest food

and wastes

– defective lysosomes cause fatal diseases

• Lysosomes carry out intracellular digestion by

– phagocytosis

– autophagy

Vacuoles:Diverse Maintenance Compartments

• Vacuoles function in general cell

maintenance

– a plant or fungal cell may have one or several

vacuoles

– food vacuoles are formed by phagocytosis

– contractile vacuoles pump excess water out of

protist

• Central vacuoles are found in plant cells

– hold reserves of important organic compounds

and water

Mitochondria and Chloroplasts

• Mitochondria and chloroplasts have similarities with

bacteria

– Enveloped by a double membrane

– Contain free ribosomes and circular DNA

molecules

– Grow and reproduce somewhat independently in

cells

Mitochondria

• Mitochondria:

– found in all eukaryotic cells, except anaerobic

protozoans

– surrounded by double membrane

• a smooth outer membrane

• an inner membrane folded into cristae

– site of cellular respiration

Chloroplasts: Capture of Light Energy

● Typically two membranes around fluid stroma, which

contains thylakoids stacked into grana

● Chloroplasts are specialized members of a

family of closely related plant organelles called

plastids

– contain chlorophyll

– found in plants and algae

– site of photosynthesis

• convert solar energy to chemical energy (sugars are

made)

Peroxisomes: Oxidation

• Peroxisomes

- specialized metabolic compartment bounded by a

single membrane

– i.e. breaks down fatty acids, breaks down toxins

• detoxify blood toxins in liver and kidneys

Ex. Alcohol

-Produce hydrogen peroxide as a by-product and

convert it to water

The Cytoskeleton

● Network of fibers that organizes structures and activities in

the cell.

● Functions in the structural support for the cell and in

motility and signal transmission

● Cell motility generally requires the interaction of the

cytoskeleton with motor proteins

• Components of the Cytoskeleton:

–microfilaments:rods of globular proteins

– intermediate filaments: ropelike strands of fibrous proteins

– intermediate filaments: hollow tubes of globular proteins

Centrosomes and Centrioles

● In animal cells, microtubles grow out of a

centrosome.

● A centrosome is a region that is often

located near the nucleus and is

considered a “microtuble-organizing

center”

Cilia and Flagella

Cilia and flagella

– function to move whole cell

– are locomotor appendages of some cells

• Cilia and flagella share a common ultrastructure

– structure consists of 9 microtubule doublets

arranged around central pair (9+2)

• Movement of cilia and flagella occurs when

arms consisting of the protein dynein move

the microtubule doublets past each other

Microfilaments (Actin Filaments)

• Microfilaments are built from molecules of the

protein actin

– microfilaments cause contraction of muscle

cells

– they also function in amoeboid movement,

cytoplasmic streaming and support for cellular

projections

Intermediate Filaments

– support cell shape

– fix organelles in place

Extracellular Components

• Plant cell walls

– Are made of cellulose fibers embedded in other

polysaccharides and protein

• Animal cells

– Lack cell walls

– Are covered by an extracellular matrix, ECM

Tight Junctions, Desmosomes, and Gap Junctions

in Animal Cells

• In animals, there are three types of intercellular

junctions

– Tight junctions

– Desmosomes

– Gap junctions