Biology 10, Las Positas College

Cells

I-Introduction
II-Cell Structure & Function Overview
III-Plasma Membrane

A. Description
B. Membrane Proteins
C. Passive transport
D. Active Transport
E. Endocytosis
F. Exocytosis

IV-Organelles and their Functions

A-Nucleus
B-Other Cytomembranes
C-Mitochondria
D-Cytoskeleton

I- Introduction
Cell Theory = 1. all living things are made up of cells. 2. Smallest living unit of structure & function of all organisms is the cell. 3. all cells arise from preexisting cells.

Functional unit of all tissues. Each can perform all essential functions of life. Cells in tissues specialize & perform wide range of 1 or more fundamental cell processes

II-Cell Structure & Function

Almost all cells have the following characteristics

1. a surrounding membrane

2. a thick fluid, cytoplasm, enclosed by this membrane

3. organelles located within cytoplasm (of eukaryotes) that carry out specific functions; 4. a nucleus (eukaryotes) or nucleoid (prokaryotes) that contains DNA

Prokaryotic vs eukaryotic

1. Prokayotic cell – no internal membranes, -> no internal organelles, -> inefficient, -> small size

Bacteria, archea

2. Eukaryotic cell – has internal membranes, -> internal organelles, especially refers to nucleus. Compartmentalization -> more efficient. Much larger.

Plant, animal, fungi, protista

organelle = internal, membrane-bound sac or compartment that serves one or more specialized functions inside cell.

III-PLASMA MEMBRANE
A. Description

B. Proteins have important, specific functions:
Transport proteins-control import and export of ions, nutrients, wastes.

C. Passive transport-does not require energy-goes down concentration gradient.

Gradient = a difference in concentration, pressure, or electrical charge between two regions.

D. Active Transport -Moves substances against the concentration gradient. Requires energy & carrier proteins.

Steps:
1. molecule attaches to carrier protein on membrane
2. molecule/carrier moves through membrane, requires energy
3. enzyme separates molecule & carrier & releases molecule on other side of membrane
4. carrier protein returns to original shape & place in membrane

E. endocytosis-bulk transport into cell

Requires energy
Cells engulf large molecules or particles and bring these substances into the cell packaged within vesicles.

F. exocytosis-bulk transport out of cell

Requires energy
Discharge of material form a cell by packing it in a vesicle and moving the vesicle to the cell surface. Often used to release hormones or neurotransmitters. Vesicle formed in cell, its membrane fuses with plasma membrane, break in membrane, product released outside cell.

Both usually receptors for substance to be incorporated. Substance attaches to receptor, indentation forms in plasma membrane, pinched off, forms vesicle with substance inside, substance shuttled to where needed or where it will be degraded

V-ORGANELLES AND THEIR FUNCTIONS

A-Nucleus

The double membrane vesicle of a eukaryotic cell that contains the hereditary material, DNA.
Control center of the cell. DNA contains instructions for building proteins which produce substances needed by cell for building, maintaining, operating and reproducing cell.

DNA inside nucleus. DNA directs the synthesis of RNA, which directs synthesis of proteins. DNA bound to proteins, forming a complex called chromatin.

B. Ribosomes – cytoplasmic organelle that provides site for protein synthesis. RNA and amino acids come together -> proteins. RNA = instructions. Amino acids = building blocks.

C. Endoplasmic Reticulum-continuous with nuclear membrane. Tubular network of membranes which are site of protein production, protein modification or lipid synthesis.

Rough ER-membrane system with ribosomes attached-site where rRNA, and substrates for protein synthesis come together and polypeptides assembled.

Smooth ER has enzymes in its interior surfaces that build and lipids and are active in detoxification.

D. Golgi Bodies-collect, modify and package molecules and prepares them for transport. Molecules come in vesicles pinched off from the endoplasmic reticulum. Once inside, molecules modified by the formation of new chemical bonds or by the addition of carbohydrates. Different parts of the stack of membranes contain enzymes that do specific jobs. When molecular products ready for transport, sorted and pinched off in separate vesicles. Each vesicle travels to its destination and fuses with another membrane.

E. Lysosomes-membrane-bounded bags of digestive enzymes. Help break down waste products. Active in remodeling . Destroy bacteria gathered by white blood cells.

F. Vacuoles

Storage compartment – food, water, etc.

G. Chloroplasts

Photosynthetic organelle. Contains chlorophyll.
Two membrane system -> inner and outer compartments. Inner membrane organizes enzymes and concentration gradients to capture light energy from sun to form sugar.
6 CO2 + 6 H2O + Energy -> C6H12O6 + 6 O2

H. Mitochondria

Break down fuel molecules, releasing energy for cell work. Powerhouse of the cell.
Two membrane system -> inner and outer compartments. Inner membrane organizes enzymes and concentration gradients to allow energy from breakdown of organic substrates (usually glucose or fatty acids) to form ATP. Requires and consumes O2. -> cellular respiration
C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + Energy

I. Cytoskeleton

Network of filaments and fibers within the cytoplasm that helps maintain the shape of the cell, move substances within cells, and anchor various structures in place. Subunits -> form and function of each.