Cells

By DJ Watts

The Cell Theory

• 1) All organisms are composed of one or more cells

• 2) Cells are the smallest unit of life• 3) All cells come from pre-existing cells

The Functions of Life

• All organisms exist in either a unicellular or multicellular form, and all organisms carry out the functions of life. These functions include:

• 1)Metabolism• 2)Growth• 3)Reproduction• 4)Response• 5)Homeostasis• 6)Nutrition

Cell Size

• Cells are relatively large, to put them in perspective, these are in decreasing size order.

CellsBacteria Viruses MembranesMolecules

Limiting Cell Size

• The factor called the surface area to volume ratio effectively limits the size of cells.

Cell Reproduction and Differentiation

• One function that many cells retain is the ability to reproduce themselves. In multicellular organisms, this allows for the possibility of growth. It also allows for the replacement of damaged or dead cells.

• Multicelluar organisms usually start out as a single cell which reproduces to form the multicellular organism

• The resulting cells go through a differentiation process to produce all the different types of cells that are necessary for the well being of the organism. This differentiation process is the result of the expression of certain specific genes but not others.

Cells and Medical Research

• There are populations of cells within organisms that retain their ability to divide and differentiate into various cell types. These cells are called stem cells.

• Some medical research has been directed towards growing large numbers of embryonic stem cells in culture so that they could be used to replace differentiated cells lost due to injury or disease. This involves therapeutic cloning.

• Successful stem cell treatment can be seen through the replacement of the damaged bone marrow of some leukemia patients.

• Ethical Issues?

Types of Cells

• Cells are divided into two groups: Prokaryotic and Eukaryotic.

• Prokaryotic cells are much smaller than Eukaryotic cells.

Prokaryotic Cells

Cell Wall and Plasma Membrane

• The prokaryotic cell wall protects and maintains the shape of the cell. In most prokaryotic cells, this wall is composed of a carbohydrate-protein complex called pepidoglycan.

• The plasma membrane is just inside the cell wall and has a composition similar to the membrane of eukaryotic cells. It controls the movement of materials in and out of the cell to a large extent, and it plays a role in the division of prokaryotic cells.

• ALL CELLULAR PROCESS IN PROKARYOTIC CELLS OCCUR IN THE CYTOPLASM.

Pili and Flagella

• Some bacterial cells contain hair-like growths on the outside of the cell wall. These structures are called pili and are used for attachment. Their main function, however, is in joining bacterial cells in preparation for the transfer of DNA from one cell to another (sexual reproduction).

• If a bacterium has flagella or a flagellum, they are long than the pili. The flagella allow the cell to move.

Ribosomes and the Nucleoid Region

• Ribosomes occur in all prokaryotic cells and they function as sites of protein synthesis.

• The nucleoid region of the bacterial cell is non-compartmentalized and contains a single, long, continuous, circular thread of DNA. This region is involved with cell control and reproduction. In addition bacteria may also contain small circular DNA called plasmids.

Prokaryotic Cell Division

• Prokaryotic cells divide by a very simple process called binary fission.

• During this process, DNA is copied, the two daughter chromosomes become attached to different regions on the plasma membrane, and the cells divide into two genetically identical daughter cells.

Review of Prokaryotic Cells

• Their DNA is not enclosed within a membrane and is one circular chromosome

• Their DNA is free; it is not attached to proteins• They lack membrane-bound organelles. Ribosomes

are complex structures within the plasma membrane, but they have no exterior membrane.

• Their cell wall is made up of a unique compound called peptidoglycan.

• They divide by binary fission.• They are small in size.

Eukaryotic Cells

Eukaryotic Cells

Cytoplasm

• All eukaryotic cells have a region called the cytoplasm that occurs inside the plasma membrane or the outer boundary of the cell.

• It is in this region that all the organelles occur.• The fluid portion of the cytoplasm between

the organelles is referred to as the cytosol.

Endoplasmic Reticulum

• The endoplasmic reticulum is an extensive network of tubules or channels that extends almost everywhere in the cell from the nucleus to the plasma membrane.

• Its structure enables its function which the transportation of materials throughout the internal region of the cell.

• The ER is of two general types: smooth and rough.

The Smooth ER

• The smooth ER has many unique enzymes embedded on its surface.

• Its functions include: 1. Production of membrane phospholipids and cellular

lipids2. Production of sex hormones 3. Detoxification of drugs in the liver4. Storage of calcium ions needed for muscle cells 5. The transportation of lipid-based compounds6. To aid the liver in releasing glucose into the bloodstream

The Rough ER

• The Rough ER has ribosomes on the exterior of the channels. These are involved in protein synthesis.

• The Rough ER is involved in protein development and transport.

Ribosomes

• Ribosomes are unique structures that do not have an exterior membrane.

• They carry out protein synthesis in the cell.• They may be found in the cytoplasm or

attached to the surface of the ER.• They consist of two subunits, RNA and a

protein.

Lysosomes

• Lysosomes are intracellular digestive centers that arise from the Golgi apparatus.

• They are sacs bound by a single membrane that contain as many as 40 different enzymes.

• Lysosomes fuse with old or damaged organelles from within the cell to break them down so that recycling of the components may occur.

Golgi Apparatus

• The Golgi apparatus consists of what appears to be flattened sacs called cistenae, which are stacked on top of one another.

• This organelle functions in the collection, packaging, modification, and distribution of materials synthesized in the cell.

• Movement= Cis Side Trans side

Mitochondria

• Mitochondria are rod-shaped organelles that appear throughout the cytoplasm.

• There roughly the size of a bacterial cell.• They have a double membrane.• The outer membrane is smooth, but the inner membrane is

folded into cristae.• Inside the inner membrane is a semi-fluid substance called

matrix. • An area called the inner membrane space lies between the

two membranes.• Most mitochondrial reactions involve the production of ATP.

Nucleus• The nucleus in eukaryotic cells is an isolated region where DNA

resides.• It is bordered by a double membrane referred to as the nuclear

envelope.• The DNA of eukaryotic cells often occur in the form of

chromosomes.• When the cell is not in the dividing process the chromosomes are

not present as visible structures. • During this phase, the cells DNA is in the form of chromatin.

Chromatin is formed of stands of DNA and proteins called histones.• This combination often results in structures called nucleosome.• These consist of 8 histones with a strand of DNA wrapped around

them and secured with a 9th histone.• Most nuclei include one or more dark areas called nucleoli . This is

where molecules of ribosomes are manufactured.

Chloroplast

• Chloroplasts occur only in plant and algae cells.• Chloroplasts contain a double membrane.• The key components of the chloroplast are DNA,

ribosomes, grana, the thylakoids, and the stroma.• A granum is made up of numerous thylakoids

stacked like a pile of coins.• The thylakoids are flattened membrane sacs with

components necessary for the absorption of light.• The fluid stroma is similar to cytosol of the cell.

Centresome

• The centresome occurs in all eukaryotic cells.• It consists of a pair of centrioles at right angles

to one another• These are involved in assembling microtubules,

which are important to the cell in providing structure and allowing movement.

• The centresome is located at one end of the cell close to the nucleus.

Vacuoles

• Vacuoles are storage organelles which form from the Golgi apparatus.

• They are membrane-bound and have many possible functions.

• They may store a number of different substances including food, metabolic waste, and toxins.

• In plants they allow an uptake of water that provides rigidity for the organism.