Introduction to the Cell

Copyright CSAN (2012), Images used with permission

The CellThe CellOutcomesOutcomes

You should be able to:You should be able to:• Briefly discuss the importance of understanding cell Briefly discuss the importance of understanding cell

structure and function in terms of health, illness and structure and function in terms of health, illness and nursingnursing

• Give definitions for organism, organ, tissue, cellGive definitions for organism, organ, tissue, cell

• Describe the basic difference between Prokaryotic & Describe the basic difference between Prokaryotic & Eukaryotic cellsEukaryotic cells

Outcomes• Describe the basic structure of a Eukaryotic cell

– Briefly describe the cytoplasm– Describe the structure of the cell membrane & briefly

explain its functions– Describe Endocytosis and Exocytosis – Describe the structure & function of the following

organelles/ cell structures:• Lysosomes ● Nucleolus• Mitochondria ● Chromatin• Centrioles ● Endoplasmic

reticulum • Nucleus ● Golgi apparatus

Levels of organisation

Think about your body:

What are its levels of organisation?

1.Chemical

2.Cellular

3.Tissue

4.Organ

5.System

6.Organism

CELL THEORYCELL THEORY 1. All living things are made up of cells & the All living things are made up of cells & the

products of those cellsproducts of those cells

2.2. All cells carry out their own life functions All cells carry out their own life functions

3.3. New cells come from other living cells New cells come from other living cells

Cell Theory is based on over 300 years of scientific investigations, beginning with Hooke in 1665

Exceptions to Cell TheoryExceptions to Cell Theory

Viruses. Cell Theory suggests

that we have to say they are not alive.

This is because a virus is not a cell.

Viruses are made protein & nucleic acid. They have no membranes, nucleus, or protoplasm. They

only appear to be alive when they reproduce after infecting a host cell. (This will be discussed in later sessions)

Mitochondria. Cell organelles that have their own genetic material & reproduce independently from the rest of the cell (This does not fit with cell theory).

Cell BasicsAll cells have:

– a cell membrane, – cytoplasm, – genetic material (DNA).

There is a stark difference between cells i.e. are they Prokaryotic or Eukaryotic

• Prokaryotic cells – no nucleus (e.g. bacteria)• Eukaryotic cells - have nucleus (e.g.neutrophil)

Other variances:– number and type of Organelles within the cell– Shape of the cell– function of the cell.

The Cell

Organelles• Secretory vesicle plasma membrane• Golgi complex nuclear envelope• Nuclear envelope• Mitochondria• Cytoplasm• Nucleus• Nucleolus• Centriole• Granular endoplasmic reticulum• Agranular endoplasmic reticulum• Ribosome• Microtubule• Lysosome

The Cell

Cell components 1: CytoplasmCytoplasm/Cytosol- This fluid like matter surrounds

the organelles

• This supports numerous microtubules that act like an internal skeleton, forming ‘motorway’ routes for substances, organelles and vesicles to travel

This allows for: - communication between components of the cell - communication between the cell and the external environment - microtubules form spindle apparatus involved in cell division

Cytoskeleton

Cell Components 2: Plasma membrane

The cell ‘plasma’ membrane maintains the boundaries of the cell

The Cell ‘Plasma’ Membrane• An essential communication link between the cell and its

surrounding environment.

• Largely made up of phospholipid molecules

• Provides specific gateways for substances to pass through, controlling the internal environment & the outflow of substances manufactured in the cell

• Contains ‘markers’ that others cells can recognize

• Proteins within the phospholipid cell wall are essential; for acceptance of water-soluble substances.

Detail of the Cell Membrane

Cell membrane proteins =special

• Part of them is Lipophilic (fat loving) which means that they can interact with lipids. These proteins can act as:

• Transporters to carry substances through the cell wall

• Channels that allow substances though the cell membrane

• Receptors that detect hormones and transmitter substances

• Enzymes that catalyze specific reactions and – Markers give the cell and identity. – Cells of the same identity group together to form tissues types (to

discussed later)

Clinical relevance point

– Think about absorption of medicines into cells--

– Liposoluble drugs ‘diffuse’ though the membrane very quickly because lipids are

attracted to a cell wall

Endocytosis and Exocytosis

Endocytosis

Exocytosis

Exocytosis

Transport through the cell wall• ENDOCYTOSIS –A small part of the cell membrane

is drawn into the cell and the cell membrane then joins with a vesicle from the outside to reform the external boundaries of the cell. This tiny droplet from the outside is then a part of the cell wall and can be released into the cell

• EXOCYTOSIS -Little sacs of substances called ‘vesicles’ join with the cell wall. For this to happen, the cell needs to take away the adjacent phospholipid layer (by endocytosis) to make room for the new part (the vesicle).

Cell Components 3: Organelles & their functions

Organelles have specific functions;

-supporting the cell and as a whole, maintaining its function

-distribution of organelles varies between cells, depending on their function.

NucleusA double layer membrane containing DNA and RNA - genetic codes.

Replication of parts of the body = depends on genetic coding

Codes = blueprint for the manufacture of proteins These proteins form a part of cell structures and tissues, enzymes, hormones, nucleic acids

Genetic codes - within the nucleus of the cell are embedded within the DNA and RNA complexes

Protein synthesis occurs within the cell cytoplasm - you need to understand this process and this is a part of your study.

The nucleus

Consists of membranes that enclose amino acids and enzymes.

Enzymes bring about chemical reactions, producing proteins and lipids.

ER is where cellular waste is broken down & converted for re-use or excretion.

Rough ER has ribosomes inserted into its membrane

Smooth ER does not have ribosomes.

Endoplasmic Reticulum ER-

Ribosomes

Ribosomes are often called the protein factories of the cell

Ribosomes are tiny. -found free in the cytoplasm or- attached to endoplasmic reticulum

a model of the two subunits that make up a ribosome

A stack of membranous sacs, associated with the ER

Takes up products made by the ER and may modify them a little -

Packages products in transport vesicles –

Packages are transported inside or outside the cell.

The Golgi apparatus

MitochondriaOriginated from bacteria-

Contain their own DNA and self replicate.

Essential for effective energy production.

Convert substances like glucose and fats to energy that can be used by the cells (i.e. ATP)

Clinical Relevance point

If we fail to feed cells with e.g. glucose, then energy will not be produced

• Imagine what would happen to our skin – as these cells need energy to constantly make new cells (to be discussed in future sessions)

• Without adequate feeding- would wounds heal?

LysosomesDigest materials:Contain Enzymes (acid hydrolases) that digest large molecules like bacteria

Breakdown cell materials Sometimes, things have to be broken down and removed to enhance the operating environment of the cell.

'Pinocytosis' - cell drinking, effectively breaking down the bacteria

'Phagocytosis' cell eating

Peroxisomes• Spherical vesicles enclosed is a membrane

• They contain several specific enzymes

• They are present in most cells – particularly large active cells in the liver (think of a

substance detoxified by the liver……)

• They ‘oxidize’ toxic molecules, removing hydrogen and transferring this to oxygen to form hydrogen peroxide.

Examples of cells

Cell SpecialisationCells become specialized to perform a particular function within an organism, usually as part of a tissue, e.g.:

Nerve cells to operate as part of the nervous system

Skin cells for waterproof protection and protection against pathogens

Cells combine efforts in these tissue types to perform a common cause.

Specialized cellsThe task of the specialized cell will determine in

what way it is going to be specialized. e.g.

Muscle cells are long and smooth in structure

White Blood Cells contain powerful digestive enzymes

Specialized cells to detect light at the back of the eye

In summary….• The structural and functional and functional unit of living

material is the………..

• It contains functional subunits called………….

• Cell function depends on the presence of specific…………..

• Groups of similar cells that perform a similar function are……………

• Structures that contain different tissues organised to perform a general function are………………..

• Groups of organs that work together to carry out a general function are…………….

SummaryIn this session we reviewed:

1. Levels of organisation

2. Cell Theory

3. Cell structure

4. Organelles and their functions