THE CELL

Cellular Organization

• Cell• Tissue – group of cells functioning

together.• Organ – group of tissues

functioning together.• Organ System – group of organs

functioning together.• Organism – group of organ

systems functioning together.

1. 1–100µm

2. Why is there a limit to cell size? a. Surface-to-volume ratio b. Distance from surface to center

Cell Size

CELL SIZE

The smaller the object the greater its ratio of surface area to volume. The nucleus can better

control a smaller cell

adult human

tallest trees

chicken egg

frog embryo

most eukaryotic cells

mitochondrionmost bacteria

virus

proteins

atoms

diameter of DNAdouble helix

nuclear pores

nucleus

CELL THEORY1.All organisms are made up of cells

2.All substances in organisms are products of cells

3.Cells come from other cells by reproduction

Microscopes and Cells• 1830’s.

–Mathias Schleiden identified the first plant cells and concluded that all plants

made of cells.

- Thomas Schwann made the same conclusion about animal cells.

Microscopes and Cells

–Robert Hooke used the first compound microscope to view thinly sliced cork cells.

• Compound scopes use a series of lenses to magnify in steps.

• Hooke was the first to use the term “cell”.

Microscopes and Cells

• 1600’s.–Anton van Leeuwenhoek first described living cells as seen through a simple microscope.

The History of the Cell

• The Cell–The basic unit of an organism–Discovery made possible by the invention of the microscope

Two Basic Cell Types

1) Prokaryote–Lacks internal compartments.

–No true nucleus.–Most are single-celled (unicellular) organisms.

–Examples: bacteria

Two Basic Cell Types2) Eukaryote

–Has several internal structures (organelles).

–True nucleus.–Either unicellular or multicellular.

unicellular example: yeast multicellular examples: plants and animals

• Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells.– All cells share certain characteristics.

• Cells tend to be microscopic.• All cells are enclosed

by a membrane.• All cells are filled with

cytoplasm.

Bacterium(colored SEM; magnification 8800x)

cell membrane

cytoplasm

Characteristics of Prokaryotic Cells.

•surrounded by a membrane and cell wall

•has no membrane enclosed organelles

Prokaryotic continued

Cells come in multiple shapes: ococci (round) o baccilli (rods) ospirilla (corkscrew)

Some cells have external whip-like flagella for locomotion or hair like pili for adhesion

coccusbaccilli

spirilla

flagella

pili

http://waynesword.palomar.edu/images/plant3.gif

“Typical” Plant Cell

“Typical” Animal Cell

http://web.jjay.cuny.edu/~acarpi/NSC/images/cell.gif

EukaryotesThe basic eukaryotic cell contains the following:

1.plasma membrane

2.cytoplasm (semifluid) (also known as cytosol)

3.cytoskeleton - microfilaments and microtubules that suspend organelles, give shape, and allow motion

4.presence of characteristic membrane enclosed

organelles

• Cells have an internal structure.– The cytoskeleton has many functions.

• supports and shapes cell• helps position and transport organelles• provides strength• assists in cell division• aids in cell movement

CYTOSKELETON

• Three main types of fibers found in the cytoskeleton

• Microtubules are long hollow tubes.• They give the cell its shape.• They work like “tracks” that organelles can ride

on• They are also necessary for mitosis (cell

division)• Intermediate filaments are smaller than

microtubules and act as supports (girders) to give the cell strength

• Microfilaments are the smallest of the three.• Tiny threads that play an important role in the

movement and division of cells

Plasma Membrane – phospholipid bilayer•A lipid/protein/carbohydrate complex providing a barrier and containing transport and signaling systems. •A selective barrier that regulates the substances that pass in and out of the cell.

Nucleus – the brainand Nucleolus

•Double membrane surrounding the chromotin and the nucleolus. •Pores allow specific communication with the cytoplasm. •The nucleolus is a site for synthesis of RNA making up the ribosome.

Mitochondria – the power house

•Surrounded by a double membrane with a series of folds called cristae which increases the surface area. •Functions in energy production through metabolism called cellular respiration. •Makes an energy molecule known as ATP• Contains its own DNA.

Rough Endoplasmic Reticulum

•A network of interconnected membranes forming channels within the cell. •Connects the nuclear membrane to the cell membrane. •Covered with ribosomes (causing the "rough" appearance) which are in the process of synthesizing proteins for secretion or localization in membranes.

•Protein and RNA complex responsible for protein synthesis – making proteins.• Can be found on rough ER or floating free in the cytosol (cytoplasm).

Ribosomes – protein

factories

Smooth Endoplasmic Reticulum

•A network of interconnected membranes forming channels within the cell. •A site for synthesis and metabolism of lipids. •Also contains enzymes for detoxifying chemicals including drugs and pesticides.

Golgi Apparatus and Vesicles

•A series of stacked membranes. •Vesicles (small membrane surrounded bags) carry materials from the RER to the Golgi apparatus. •Vesicles move between the stacks while the proteins are "processed" to a mature form. •Contain enzymes that make final additions to proteins.•Vesicles then carry newly formed membrane and secreted proteins to their final destinations.

Vacuoles

Membrane surrounded "bags" that contain water and storage materials .

Lysosomes – suicide bag

• The main function of these microbodies is

digestion. • Lysosomes break down cellular waste products and debris from outside the cell into simple compounds, which are transferred out into the cytoplasm as new cell-building materials.

• Carries out apoptosis – “Cell Suicide”-If a cell is damaged or functioning improperly and harming the organism, the nucleus sends a signal for all of the Lysosomes to move to the cell membrane and open up.

• This causes the digestive enzymes to eat holes in the cell membrane caused the death of the cell.

• Can also happen when a cell gets to old- sometimes referred to as programmed cell death.

Lysosomes – suicide bag

• Centrioles are tubes found in the centrosomes.

• Centrioles help divide DNA • Centrioles form cilia and flagella

Centriole

Cell wall

Cell WallsThis surrounds (on the outside) the cell membraneFound in plants, algae, fungi, and most bacteriaThis gives support, shape, and protection to the organismThis cell wall takes the place of an internal skeletonCell walls are made of different substances based on the type of organism

In plants and Algae, the cell wall is made of celluloseIn Fungi, cell walls are made of chitinIn bacteria, cell walls are made of peptidoglycan

Chloroplast

ChloroplastsHighly compartmentalized (like Mitochondria) to increase surface area for chemical reactionsThey contain disc-shaped sacs called Thylakoids, which contain chlorophyll Chlorophyll is a pigment that gives plants their green appearance and absorb light energy as part of photosynthesisChloroplasts also have their own DNA and Ribosome's, so they may have been captured in a similar manner to mitochondriaRemember, plants have BOTH Mitochondria AND Chloroplasts

Prokaryotes & Eukaryotes

• Similarities & differences

– Both surrounded by plasma membrane, but very different

– Prokaryotes – Archaebacteria and Eubacteria

– Eukaryotes – everything else

Plant & Animal Cells

• Similarities

– Both constructed from eukaryotic cells

– Both contain similar organelles

– Both surrounded by cell membrane

Plant & Animal Cells

• Differences

– Plants have• Cell wall – provides strength & rigidity

• Have chloroplasts, photosynthetic

–Animals have• Other organelle not found in plants (lysosomes formed from Golgi)

• Centrioles, important in cell division

cell membrane

• Cell membranes are composed of two phospholipid layers.– The cell membrane is made of a phospholipid

bilayer.– There are other molecules embedded in the

membrane.

– The fluid mosaic model describes the membrane.

protein

cholesterol

proteincarbohydratechain

protein channel

Phospholipid Bilayer

Cell membranes are composed of two phospholipid layers.

The cell membrane is selectively permeable.

Some molecules can cross the membrane while others cannot.

Homeostasis• Balance between all life activities.

• Things that influence equilibrium:1.Size of particles2.Solubility in water3.Conditions in and out of the cell4.Structure of the membrane

(pore size)• Passive and active transport

maintains homeostasis

Diffusion

The movement of molecules from an area of high

concentration to an area of low concentration.

Factors that Affect Diffusiono Concentration

o Temperature

o Pressure

Special types of diffusion

• Osmosis the special diffusion of water across a selectively permeable membrane. It is a passive transport (needs no energy)

• Turgor Pressurethe pressure that builds up in a plant cells as a result of the osmosis of water inward into a plant cell. This gives the plant firmness.

Diffusion and osmosis are types of passive transport.• There are three types of solutions.

• isotonic

Diffusion and Osmosis

• hypotonic

• hypertonic

Isotonic Solution

Hypotonic Solution

Hypertonic Solution

• Some molecules can only diffuse through

transport proteins.• Some molecules cannot easily diffuse across the cell membrane.

• Facilitated diffusion is diffusion through transport proteins.

Diffusion and Osmosis

• Active transport requires energy input from a cell

and enables a cell to move a substance against its

concentration gradient.

• Passive transport requires no energy from the cell.

• Active transport is powered by chemical energy (ATP).

Active Transport, Endocytosis, and Exocytosis

• Cells use active transport to maintain homeostasis.

• Active transport occurs through transport protein pumps.

• A cell can import and export large materials or large

amounts of material in vesicles during the

processes of endocytosis and exocytosis.• Cells use energy to transport material in vesicles.

• Endocytosis is the process of taking material into the cell.

Active Transport, Endocytosis, and Exocytosis

• Phagocytosis is a type of endocytosis.