Introduction Introduction Introduction Introduction

to the Cellto the Cellto the Cellto the Cell

• An adult human body has approx. 75 TRILLION cells!

• Cells in different tissues vary considerably in size and shape (and functions)

• We will focus on a “typical” cell

(unspecialized)

NUCLEUS

• membrane-bound organelle that contains most of the cell’s DNA– visible with light microscope– visible with light microscope

– enclosed by a nuclear envelope

– contains all of the information for cell to function

NUCLEAR ENVELOPE

• double membrane which encloses the nucleus– lipid bilayer membrane w/specific proteinsw/specific proteins

– is perforated by pores which regulate molecular traffic into and out of the nucleus

CHROMATIN• complex of DNA and proteins which make up chromosomes

CHROMOSOMES

• compacted, coiled up chromatin;

• long threadlike structures composed of chromatin and composed of chromatin and found in nucleus;

• visible under microscope;

• form as a cell prepares to divide

• human cells have: 46 (23 pairs)

NUCLEOLUS

• spherical region in the nucleus– visible when cell is NOT dividing– visible when cell is NOT dividing

– where ribosomes form

RIBOSOMES:• the sites of protein synthesis

– made in the nucleolus

– cells with high rates of protein

synthesis have large numbers of

nucleoli & ribosomes (e.g. human nucleoli & ribosomes (e.g. human

liver cells have millions)

– may be attached to the ER or

scattered throughout cytoplasm

ENDOPLASMIC RETICULUM (ER):

• extensive network of tubules and sacs

• may be “rough” (ribosomes) or “smooth” (no ribosomes)

• transports molecules within cell• transports molecules within cell

Smooth ER:

• synthesizes lipids, phospholipids,

steroids

• participates in carbohydrate • participates in carbohydrate

metabolism

• detoxifies drugs and

poisons

Rough ER:

• manufactures secretory proteins and

membranes

GOLGI APPARATUS:

• organelle made of stacked, flattened

membrane sacs

• finishes, sorts and ships many cell products• finishes, sorts and ships many cell products

• vesicles arrive from the ER and fuse with the Golgi membrane

LYSOSOMES• the “garbage disposals of the cell”

• contain powerful enzymes that break down nutrients or foreign particles

• recycle the cell’s own organic material;

• destroy cells• destroy cells

VESICLES / VACUOLES:

• membrane-bound sacs formed by the inward folding of the cell membrane

• contain liquid or solid material

• Golgi apparatus and ER also form vesicles

PEROXISOMES:• contain special

enzymes for specific

metabolic pathways,

including:

-synthesis of bile acids -synthesis of bile acids

(used to digest fats);

-detoxifying hydrogen

peroxide and alcohol;

MITOCHONDRIA:

• sites of cellular respiration (energy

from nutrients is released and from nutrients is released and

converted into ATP!

• the # in cells varies and is related to

the cell’s metabolic activity

• inner membrane is

convoluted and

contains enzymes

involved in cellular

respiration

• inner membranes many • inner membranes many

infoldings are called

cristae; they increase

the surface area for

cellular respiration

reactions to occurMitochondria in a human liver cell

MICROTUBULES & MICROFILAMENTS

• make up the cytoskeleton

• network of fibers throughout cytoplasmcytoplasm

• structural support to cell; maintain shape

• involved in cell motility (movement)

Microtubules:• straight, hollow rods made of protein

• can serve as “tracks” to guide organelle

movement;

YellowYellow: nucleus: nucleus

GreenGreen: microfilaments throughout cytoplasm: microfilaments throughout cytoplasm

movement;

• involved in separation of chromosomes in

cell division; make up CENTRIOLES

• responsible for beating of flagella & cilia

Cilia and Flagella:

► CILIA: fringe the surfaces of some epithelial (lining) cells

-tiny, hairlike structures

-beat in succession producing a wave of motion (e.g. sweep dust and of motion (e.g. sweep dust and debris out of respiratory tubes)

► FLAGELLA: longer; usually single structures

-move in wavelike motion to propel a cell