A TOUR OF THE CELL

Cell Theory

All organisms are composed of one or more cells

Cells are the smallest living units of

all living organisms

Cells arise only by division of a previously

existing cell

Cell Size

relatively small because as size increases,

volume increases much more rapidly.

longer diffusion time

How are cells studied

Microscopy

Magnification

Resolution/resolving power

Cell fractionation

Technique that involves separation of

cellular organelles

Visualizing Cells

Resolution - minimum distance between two

points can be apart and be

distinguished as two separate points

Magnification how much larger an object is

made to appear compared to its

real size

General types of Microscopes

Compound light microscope

Electron microscope

Transmission EM

Scanning EM

Visualizing Cells

Cell Characteristics

Genetic material (DNA)

Single, circular in prokaryotes

double helix in eukaryotes

Cytoplasm fills cell interior

sugars, amino acids,

proteins organelles

Plasma membrane encloses the cell phospholipid bilayer

Living organisms as made up of either

Prokaryotic or Eukaryotic cells

Prokaryotic

(pro=before ; karyon=kernel)

Eukaryotic

(Eu=true; karyon=kernel)

Found only in bacteria and cyanobacteria Found in Protista, Fungi, Plantae and

Animalia

No true nucleus;lack nuclear membrane True nucleus; bounded by nuclear membrane

Genetic material in nucleoid region Genetic material within nucleus

No membrane-bound organelles Contains cytoplasm with cytosol and

membrane-bound organelles

Generalized Prokaryotic and Eukaryotic Cells

Generalized Animal and Plant Cells

Nucleus

Bound by nuclear membrane (two phospholipid bilayers)

Nuclear pores protein gatekeepers

Usually proteins going in and RNA going out

Repository for genetic material organized

w/ proteins = chromosomes

Directs activities of the cell

Usually single, some cells several, RBC none

Nucleolus - region of intensive ribosomal RNA synthesis

Chromosomes

DNA of eukaryotes is divided into linear chromosomes.

exist as strands of chromatin, except during cell

division

associated with packaging histones, packaging

proteins

nucleosomes

Endomembrane System

Includes:

Nuclear envelope

Endoplasmic reticulum

Golgi apparatus

Lysosomes

Vacuoles

Plasma membrane

(not actually an endomem. but related to the system)

Importance:

Compartmentalizes cell, channeling passage of molecules through cells interior.

Rough ER - studded with ribosomes

Smooth ER - few ribosomes

Endoplasmic reticulum

Extensive membranous network of tubules and sacs (cisternae)

Smooth ERSynthesizes lipids, phospholipids and

steroids

Participates in

carbohydrate

metabolism

Stores calcium ions for muscle contractionDetoxifies drugs

Rough ERManufactures secretory proteins

Manufactures

membrane

Golgi apparatus

Modifies, stores, routes, collects, products of ER

Distribute molecules synthesized at one location in the cell and utilized at

another location

Stacked, flattened membranous sacs (cisternae)\ Has distinct polarity, cis face and trans face

Modifies, stores, routes, collects, products of ER

Distribute molecules synthesized at one location in the cell and utilized at another location

SYNTHESIS OF MEMBRANE COMPONENTS AND THEIR

ORIENTATION ON THE RESULTING MEMBRANE

Lysosomes - membrane-bound vesicles containing digestive enzymes

(lipase, protease, carbohydrase,nuclease)

Microbodies - enzyme-bearing, membrane-enclosed vesicles.

Peroxisomes - contain enzymes that catalyze the removal of electrons and

associated hydrogen atoms

- Peroxide-producing oxidases

- catalase

Vesicles

Cytoplasm

Phagocytosis

Foodvesicle

Golgiapparatus

Lysosomes

Plasmamembrane

Digestion ofphagocytizedfood particles

or cells

Endoplasmicreticulum

Transportvesicle

Old or damagedorganelle

Breakdownof old

organelleExtracellularfluid

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Relationship among Endomembranes: A Summary

Nuclear

envelope

Golgi apparatus

Rough ER Smooth ER

Plasma membraneLysosomes

Vesicles

Vesicles

Membrane and secretory proteins produced

in ER are transported in

Fuse with the forming

face of

Pinch off maturing face

Give rise toFuse with and add to plasma membrane

and may release cellular products to outside

Is an extension of Is confluent with

Ribosomes

Ribosomes are RNA-protein complexes composed of

two subunits that join and attach to messenger RNA.

site of protein synthesis

assembled in nucleoli

Organelles With DNA

Mitochondria

bounded by exterior and interior membranes

interior partitioned by cristae

Chloroplasts

have enclosed internal compartments of stacked

grana, containing thylakoids

found in photosynthetic organisms

Mitochondria

"Powerhouse of the cell" - cellular metabolism

With outer and inner membranes, cristae

Have their own DNA

Chloroplasts

Chloroplasts are larger and more complex than mitochondria

Grana closed compartments of stacked membranes

Thylakoids disc shaped structure light capturing pigment

Stroma fluid matrix

Endosymbiosis

Endosymbiotic theory suggests engulfed prokaryotes

provided hosts with advantages associated with

specialized metabolic activities.

Theory of Endosymbiosis

Evidence for the endosymbiont theory is that

mitochondria and chloroplasts:

- Are appropriate size to be descendants of eubacteria.

- Have inner membranes similar to those on prokaryotic plasma membranes.

- Replicate by splitting, as in prokaryotes.

- DNA is circular and different from the DNA of the cell's nucleus.

- Contain their own components for DNA transcription and translation into proteins .

- Have ribosomes similar to prokaryotic ribosomes.

- Molecular systematics lend evidence to support this theory.

- Many extant organisms are involved in endosymbiotic relationships.

Cytoskeleton

Network of protein fibers throughout the cytoplasm

supporting cell shape, anchoring organelles, motility

Constructed from 3 types of fibers:

Microtubules Microfilaments Intermediate filaments

Microtubule

2. Cellular support 3. Make up centrioles

in animal cells

1. Cell motility (cilia and flagella)

4. Separation of

chromosomes during

cell division

Structure of cilia and flagella

Microfilaments(globular actin and long chain F actin)

Participates in

muscle contraction

Provides support

localized

contraction of cells

Intermediate filaments

Framework

of cytoskeletonReinforce

cell shape

Fix organelle position

Plant Cells

Central vacuole

often found in the center of a plant cell, and serves as a storage facility for water and other materials

Cell wall

primary walls laid down while cell is growing

middle lamella glues cells together

secondary walls inside the primary cell walls after growth

Plant Cell

Animal Cells

Animal cells lack cell walls.

form extracellular matrix

provides support, strength, and resilience