NOTES FOR BIOLOGY 1001

SECTION 005

Spring 2005

DR. STEVEN POMARICO, INSTRUCTOR

PART 1D

CHAPTER 4

CELL STRUCTURE AND FUNCTION

>>>Some of the basics

Three generalization comprise the cell theory.

1) Every organisms is made up of one or more cells.

2) The cell is the smallest unit having all the properties of life.

3) The continuity of life comes from growth and division of cells.

The plasma membrane contains the cell but still allows the cell to interact with its environment. (See fig 4.4)

---Plasma membrane is the membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell’s chemical environment.

Most membranes including the plasma membrane are composed of proteins and lipids.

>>>Genetic material in cells is deoxyribonucleic acid (DNA)

Where is the DNA stored?

Remember

---Prokaryotic versus Eukaryotic

PROKARYOTES	EUKARYOTES
Found only in the Kingdom Monera	Found in the Kingdoms Protista, Fungi, Plantae, and Animalia
No nucleus or nuclear envelope	Nucleus with a nuclear envelope
DNA in a “nucleoid region”	DNA within the nucleus
No organelles or internal membranes	Contains cytosol with membrane-bound organelles

---Nucleoid is a dense region of DNA in a prokaryotic cell

---Cytoplasm is the entire region inside the cell membrane and outside the the region containing the DNA.

>>>Eukaryote cells are compartmentalized

Why compartmental organization?

-Provide localized environmental conditions necessary for specific metabolic process.

-Sequester reactions, so they may occur without interference from incompatible metabolic processes elsewhere in the cell.

These compartments inside of the eukaryotic cell are organelles

---Organelles are one of several compartments suspended in the cytoplasm of eukaryotic cells.

1) Nucleus

2) Endoplasmic reticulum

3) Golgi complex

4) Vesicles

5) Mitochondrion

6) Chloroplasts (in plants)

>>>>>The nucleus is the compartment that contains the cell’s genetic library (See fig 4.11)

---Nucleus is a conspicuous (usually) membrane-bound cellular organelle in eukaryotic cells. The nucleus contains most of the genes that control the cell.

---Nuclear envelope is a double membrane which encloses the nucleus of a eukaryotic cell

---Nucleolus is a spherical shaped region in the nucleus where eukaryotic ribosomes are assembled.

-May be two or more per cell.

-Sites of ribosome production

---Chromatin is a complex of DNA and histone proteins, which make up chromosomes in eukaryotic cells. In non-dividing cells, the chromatin appears as a mass of diffuse stained material.

---Chromosomes are long threadlike associations of genes, composed of chromatin and found in the nucleus of eukaryotic cells.

Each species has a specific number of chromosomes (46 for humans)

>>>>>Many cell organelles are connected through the endomembrane system

Endomembrane system

-components include:

-Nuclear envelope

--Endoplasmic reticulum (rough and smooth types)

-Golgi apparatus

-Lysosomes

-Vacuoles

All of the components are related either directly or indirectly

>>>>>The endoplasmic reticulum manufactures membranes and performs other vital biosynthetic functions

---Endoplasmic reticulum (ER) (See fig 4.14) is an extensive membranous network of tubules and sacs

-Largest part of the cell’s membrane system

-Found in two forms smooth ER and rough ER.

-Smooth ER (because there are no bound ribosomes attached)

Function

Synthesis of lipids (especially phospholipids and steroids)

-Rough ER (because of the presence of bound ribosomes)

Functions

Manufacture of membranes

Synthesis of secretory proteins (made on the ribosomes)

The pathway of a secretory protein:

1. Protein synthesized by a bound ribosome

2. The newly synthesized protein moves through the ER membrane into the ER

3. A vesicle carrying the protein is pinched off the ER and travels to the Golgi bodies.

>>>>>The Golgi bodies finish, sort and ship many cell products (See fig 4.15).

---Golgi body is an organelle made of stacked, flattened membranous sacs, that modifies, stores, sorts, and routes products of the ER.

The Golgi body has two sides or faces, a cis-face and a trans-face

-The cis-face is the “receiving” face for transport vesicles arriving to the Golgi from the ER

-The trans-face is the “shipping” face for transport vesicles leaving the Golgi.

>>>>All of the components 0f the endomembrane system are connected either directly or indirectly

-Directly through physical contact

-Indirectly through vesicles

---Vesicles are membrane-enclosed sacs that are pinched off portions of membranes. Vesicles are formed at one site and move to a membrane at another site.

>>>One type of vesicle which “leaves” from the Golgi complex is the lysosome (see fig. 5-14)

---Lysosomes are membrane-bound organelles which are digestive compartments that digest all major classes of macromolecules.

Functions of lysosomes:

1. Intracellular digestion

---Food vacuoles are formed by phagocytosis of a food particle

2. Recycling of cellular material

3. Programmed cell destruction

>>>>>Peroxisomes consume oxygen in metabolic functions

---Peroxisomes are membrane-bound organelles which contain enzymes for the breakdown of fats and proteins.

Functions:

1. Oxidation of molecules

A. Breakdown of fatty acids

2. Breakdown of peroxide (H₂O₂)

3. Detoxification

Alcohol

>>>>>Mitochondria and chloroplasts are the main energy transformers of cells

(cellular power company)

General features of both organelles:

-Double membrane

-Membranes are not part of the endomembrane system

-Contain ribosomes and DNA

Make some but not all of their proteins (10-20%)

-Semi-autonomous

Can grow and reproduce

---Mitochondria (See fig. 4.16) are organelles which use energy extracted from organic macromolecules (food) to produce ATP

Mitochondrial Features:

-Size 1-10 micrometers

-Number per cell varies with metabolic activity

-Can move and change shape

-Inner membrane is highly folded to increase surface area. The infolded structures are called cristae

-Space between the outer and inner membranes is called the intermembrane compartment

-Space inside the inner membrane is called the matrix

---Chloroplasts (See fig 4.17) are chlorophyll containing organelles which are the sites of photosynthesis

Chloroplast Features:

-Size 2.0-5.0 micrometers

-Number per cell varies with metabolic activity

-Can move and change shape

-Space inside the inner membrane is called the stroma.

---Stroma is the viscous fluid between the inner membrane

---Thylakoids are third membrane system found in the chloroplast stroma. They are shaped like flattened sacs.

---Grana are stacks (granum = 1 stack) of thylakoids in a chloroplast.

>>>>>The cytoskeleton provides structural support and functions in cell motility.

---Cytoskeleton (See fig 4.20)

General functions:

-Mechanical support for the cell

-Allows the cell to maintain shape and change shape

-Involved with organelle movement and cell movement by interacting with specialized proteins called motor proteins (See fig. 4.23).

General features:

-Constructed from at least three types of fibers: microtubules (thickest), microfilaments (thinnest), and intermediate filaments (in between size)

(See fig 4.21)

>>>>>Plant cells are surrounded by cell walls (See fig 4.27)

Composed of cellulose fibers embedded in a matrix of other polysaccharides and proteins.

Development of the cell wall:

-Young plant cell secrete a thin flexible primary cell wall

-As the plant cells mature and stop growing they may add a hardening substance to the primary cell wall and/or secrete a secondary cell wall between

the primary cell wall and the plasma membrane.