Cellular Structure and Function.

Chapter 7

Cell Discovery and Theory.

A cell is the basic structural and functional unit of all living organisms.

The human body is made of trillions of cells that are too small to see with naked eye. Because of their size , cells were unknown to scientist before the invention of the microscope.

The term cell came from a scientist by the name of Robert Hooke. (cellulae)

The Cell Theory.

A fundamental idea of modern biology that includes three principles:

1. All living organisms are composed of one or more cells.

2. Cells are the basic unit of structure and organization of all living organisms.

3. Cells arise form previously existing cells, passing their genetic material on to their daughter cells.

What Discoveries led to the Cell Theory?

In 1838, a German scientist by the

name of Matthias Schleiden studied plants and concluded that all plants are made up of cells.

Soon after, A scientist by the name

of Theodor Schwann reported that animal tissues are made up of cells as well.

Microscope Technology.

Compound light Microscopes:

• Uses a series of lens to magnify an object.

• When light passes through each lens, it magnifies the image of the previous lens.

Electron microscope: • Invented in the 1940’s.

• Doesn’t use lens.

• Uses a magnet to transmit a beam of electrons at the image to magnify it.

• The Scanning Electron microscope ( improvement) –Produces 3D images.

Basic Cell Types. All cells have different sizes, shapes, and functions, but they all have a

plasma membrane.

(A boundary that helps control what enters and leaves the cell.)

Cells are grouped into two broad categories based on their internal structure.

Prokaryotic cells Eukaryotic Cells

OR

Prokaryotic Cells:

• Simple cells with no specialized Structures are known as

prokaryotic cells.

• Unicellular organisms (bacteria) are prokaryotic cells therefore called Prokaryotes.

• Cell Functions for these cells take place in the plasma membrane.

*Similar to the first cells on earth.

Eukaryotic Cells:• Larger and more complex than

prokaryotic cells.

• Organisms made up of eukaryotic cells are called Eukaryotes. (can be unicellular or multicellular.)

• Contain a nucleus and other organelles.

• Specialized structures that carry out specific functions.

• Nucleus contains the genetic material for the cell.

The Plasma Membrane

Function : • A critical structure for the survival of a cell is the plasma membrane.

It allows the cell to maintain homeostasis ( stability).

*How waste leaves and nutrients enter.

It is a Thin, flexible boundary between a cell and its watery Environment.

•Recap! the plasma membrane is how waste leaves the cell and how nutrients comes in.

The plasma membrane is selectively permeable. Which means that it allows some substances to pass through while keeping other substances out of the cell.

Structure of the Plasma Membrane

•Plasma membrane is made up of two layers of phospholipids arranged tail-to-tail in what is called a phospholipid bilayer. (Allows for survival in watery environment)

Each phospholipid has a polar head and two non-polar tails.

Polar head attracts to water and non-polar tails repel water.

Arranged so that the polar heads face the side closest to water that is inside and outside the cell.

Non polar tails face the side farthest from water.

How does the phospholipid bilayer function?

•It forms a barrier that is polar on the surface and nonpolar in the middle.

•Substances that can dissolve in water will not pass through.

•Separates the outside environment of the cell to the inside environment of the cell.

What else is in the plasma membrane? • Inside of the plasma membrane you can find

1. Cholesterol -

2. Proteins – found on inner and outer surface. On the outer surface it is called a receptor ( send signals on the inside of the cell). On the inner surface it functions as support ( gives the shell its shape).

3. Carbohydrates

Transport Proteins

• Proteins that create a tunnel through the plasma membrane are called transport proteins. • Move needed substances or

waste through.

• Contribute to selective permeability.

Cholesterol:

•Cholesterol prevents the fatty-acid tails from sticking together. ( keeps it fluid)

•Helps maintain homeostasis.

Cell Structure and Organelles

The environment inside the plasma membrane is a semifluid material called

the Cytoplasm.

A structure within the cytoplasm called

the cytoskeleton is a network of long thin protein fibers that provide an anchor for organelles inside the cell. * the cells shape depends on the cytoskeleton.

Two types of protein fibers make up the cytoskeleton.

1. Microtubules: Long, hollow protein cylinders that form a firm skeleton for the cell. ( Assist in the movement of substances in the cell).

2. Microfilaments: thin protein threads that help give a cell shape and enables parts of the cell to move.

There are two types of Eukaryotic Cells:

Plant Cell Vs. Animal Cell• The same organelles are found mostly in both

cell types. • There are a few differences:

1. Centrioles and lysosomes are only found in animal cells.

2. Chloroplast and cell wall are only found in plant cells

Cellular Organelles

• The Cells Managing Structure.

• Contains most of the cells Genetic material (DNA). • DNA Defines the Cell and controls the

production of proteins. • The Nucleus is

Enclosed by a Nuclear Envelope that has nuclear pores ( Allows substances to move in and out of the Nucleus).

• Contains a nucleolus that Produce ribosomes

*Present in both cell types

• Present in both cell types. • Produce proteins. • Made up of two

components:1.RNA (genetic material) 2.Proteins

• Some float freely in the cytoplasm and others are bound to the

Endoplasmic reticulum.

• A rough endoplasmic reticulum- a membrane system of folded sacs and channels which ribosomes are attached to.

• Smooth endoplasmic reticulum- Has no ribosomes attached. Produces complex carbohydrates and lipids.

• Modifies, sorts, and packs proteins into sacs called Vesicles. • Sacs fuse to

plasma membrane and ship proteins out of the cell.

• Act as a temporary storage for materials in the cytoplasm.

• Can store food, waste, and other materials needed by the cell.

Lysosome • Contain Substances that digest excess or worn-down organelles and food particles.

• Also digest bacteria and viruses that enter the cell.

Centriole

• Organelles made up of microtubules that function during cell division.

• Usually found near the nucleus of the cell.

* Only in animal cells.

Mitochondria

• Power house of the cell. • Converts fuel particles (Sugars)

into usable energy for the cell. • Has an outer membrane and in

inner membrane with many folds (provides a larger surface area)

Chloroplast

• Capture light energy (sun) and converts it into chemical energy through photosynthesis.

* Only in plant cells

Cell Wall

• Mesh of fibers that surrounds the plasma membrane.

• Protects and supports the cell.

• Made up of carbohydrates called cellulose.

*Only in plant cells.

Some animal cell surfaces have

Cilia or Flagella that extends beyond the plasma membrane.

• Cilia are short projections that look like hairs ( move back In forth, similar to the motion of the oars of a rowboat.)

• Flagella are longer, whip like projections that propel the cells.

* Both are composed of microtubules.

Flagella

Cellular Transport

DiffusionThe Net movement of particles from an area where there are many particles to an area where there are fewer particles of that substance.

• The Amount of substance in a particular area is called Concentration.

*Substances move from areas of high concentration to low concentration.

Condition in which there is continuous movement but no overall change is called Dynamic Equilibrium.

Main factors that affect the rate of diffusion.

• Concentration • Temperature • Pressure

When concentration is high, diffusion occurs more quickly because there are more particles that collide with one another.

*Same with temperature and pressure.

Diffusion Across the Plasma Membrane

*Remember that water can move across the membrane but other particles cannot.

Facilitated diffusion is another form of transport that uses transport proteins to move ions and small molecules across the plasma membrane.

With this method, substances move through a water-filled transport

protein, called a channel protein.

It opens and closes to allow substances to diffuse through the membrane.

Another type of transport

protein is called a carrier protein.

This protein changes shape as the diffusion process continues to help move particles through the membrane.

Facilitated diffusion requires NO ENERGY because the particles are moving down the concentration gradient. ( high -> low)

This is known as passive transport.

Osmosis: Diffusion of Water

The Diffusion of water across a selectively permeable membrane is called

Osmosis.

*The regulation of water movement is an important factor for maintaining homeostasis.

How does it work?

• A solution consist of a solvent ( water) and solutes.

• Water is the Solvent in a cell and its environment.

• Concentration is the measure of the amount of solute in a solvent.

Pink= water molecules Dotted line= Selectively permeable membranePurple = Sugar molecules

Water molecules will move to the side with the least concentration of water molecules. (right)

As the water moves the concentration of the sugar molecules will decrease and the water will continue to move until it reaches dynamic equilibrium.

Cells in an Isotonic SolutionWhen a cell is in a solution that has the same conc. Of water and solutes ( ions, sugars, proteins, etc.) as its cytoplasm it is said to be

in an isotonic solution.

Iso =equal

Water still enters the cell, but it moves in and out at the same rate.

Cell is at equilibrium and maintains its original shape. (most cells are in an isotonic solution, in the body)

Cells in a Hypotonic Solution

When a cell is in a solution that has a lower concentration of solutes as its cytoplasm it is said

to be in an Hypotonic solution.

Hypo= under

*Because they have ridged cell walls for support, plant cells do not burst in a hypotonic solution.

Cells in a Hypertonic Solution.

When a cell is in a solution that has a lower concentration of water and as its cytoplasm it is said to be in an

Hypertonic Solution.

• During osmosis net movement of water is out of the cell.

• Cells will shrivel.

Active Transport

When substances must move from places of lower concentration to that of higher concentration it requires energy. This is

called Active transport.

Carrier protein, commonly

called pumps. Use energy to transfer substance against their conc. Gradient (low -> high).

Transport of large molecules

If substance is too big to be moved by passive or active transport, it can enter the cell through a process called

Endocytosis.

A cell surrounds a substance in the outside environment, enclosing it with a portion of the plasma membrane.

Exocytosis is the secretion of materials at the plasma membrane.