Transcript A Tour of the Cell

A Tour of the Cell
Overview: The Cell

Cell: the basic unit of all living organisms

2 types:


Prokaryotic
Eukaryotic

All cells have several basic features


A plasma membrane
Contain cytosol: jellylike substance where
organelles & other components are found

Contain chromosomes

Have ribosomes

Major difference: location of DNA

Eukaryotic: membrane enclosed (nucleus)

Prokaryotic: not membrane enclosed

Region called nucleoid

Other differences:

Eukaryotes have organelles

Eukaryotes are generally larger
The Eukaryotic Cell
The Nucleus


Contains genes of the cell
Enclosed by nuclear envelope




Double membrane
Perforated by pores
DNA is organized into chromosomes inside
nucleus
Nucleolus: makes ribosomes
Ribosomes



Made of rRNA & proteins
Carry out protein synthesis
Cells with high rate of protein synthesis
have high number’s of ribosomes


Human pancreas cells have a few million
ribosomes
Can be free or attached
The Endoplasmic Reticulum

Network of membranes

2 types:


Smooth ER: lacks ribosomes
Rough ER: contains ribosomes on outer
surface
Functions of Smooth ER

Diverse metabolic processes




Synthesis of lipids
Metabolism of carbohydrates
Detoxification of drugs & poisons
Cells that synthesize steroids and/or
hormones are rich in smooth ER

Liver cells help detoxify drugs & poisons




Adds hydroxyl group to drug/poison
Makes molecules more soluble
Alcohol creates this type of response
Induces smooth ER to work quickly
Increases rate of detoxification
 As a result: increases tolerance

Functions of Rough ER

Make proteins that are secreted by the cell


Proteins get separated from proteins that
remain in cell


Ex. Pancreatic cells secrete insulin
Place in transport vesicles
Also makes phospholipids
The Golgi Apparatus




After leaving ER, many transport vesicles
head here
The center of manufacturing,
warehousing, sorting, & shipping
Products of ER get modified, stored & sent
to their destinations
Made of flattened membrane sacs called
cisterae

Has a distinct polarity

Cis face  receiving

Trans face  shipping

Cis face is usually near ER
Lysosomes



A membranous sac of hydrolytic enzymes
These enzymes work best in acidic pH
Hydrolytic enzymes & membrane are
made by rough ER


Some actually bud off trans face of Golgi
apparatus
Carry out intracellular digestion


Ex. Assist in phagocytosis
Ex. Recycle cell’s organic material
Vacuoles

Membrane bound vesicles with many
functions




Store food
Contractile vacuole  pumps water out of cell
In plants & fungi  hydrolysis
Central vacuole  stores a variety of
compounds
Mitochondria

Found in nearly all eukaryotes




Enclosed by 2 membranes




Some have single, large mitochondrion
Most have hundreds or thousands
Number correlates with level of metabolic
activity
Outer  smooth
Inner  folded into cristae
Has its own DNA
Serves as site of cellular respiration
Chloroplasts


Site of photosynthesis
Specialized plastid – group of closely
related plant organelles





Leucoplast: colorless; stores starch, lipids, &
proteins
Chromoplasts: have pigments that give fruits
& flowers a yellow or orange hue
Chloroplasts: have green pigments
Enclosed by 2 membranes
Has its own DNA
Peroxisomes

Specialized metabolic compartment bound
by a single membrane

Transfers hydrogen to O2 to form H2O2

H2O2 is toxic

Also has enzymes that convert it to H2O
Cell-to-Cell Connections

Tight junctions: connect cells by tightly
pressing them together

held in place by special proteins

Prevents extracellular fluid from leaking

Desmosomes: fasten cells together into
strong sheets

Ex. Muscle cells

Gap junctions: cytoplasmic channels
from one cell to another

Necessary for communication