Introduction to the Cell

Copyright CSAN (2005), Images used with permission

The CellThe CellObjectivesObjectives• Briefly discuss the importance of Briefly discuss the importance of

understanding cell structure and function understanding cell structure and function in terms of health, illness and nursingin terms of health, illness and nursing

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

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

Objectives• Describe the basic structure of a Eukaryotic cell

– Briefly describe the cytoplasm– Describe 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 the Cell TheoryExceptions to the Cell Theory• Viruses. According to the Cell Theory we have to say

they are not alive because a virus is not a cell. Viruses are made protein & nucleic acid, but have no membranes, nucleus, or protoplasm. They appear to be alive when they reproduce after infecting a host cell. (This will be discussed in later sessions)

• Mitochondria. These cell organelles (small structures inside the cell) have their own genetic material & reproduce independently from the rest of the cell

Cell Basics• The Prokaryotic-Eukaryotic difference

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

neutrophil)

• All cells have– a cell membrane, – cytoplasm, – genetic material (DNA).

• Other variances- – Organelles present in the cell, the shape of the cell, or

the 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• Cytoplasm- a jelly like matrix within the cell

– Includes structures called organelles (little organs)

– Fluid like cytosol surrounds the organelles

Numerous microtubules within the cytosol act like a sort of internal skeleton, forming ‘motorway’ routes for substances, organelles and vesicles to travelAllows for: - communication between components of the cell - communication between the cell and the external environment - microtubules form spindle apparatus involved in cell division

The cytoskeleton

cell wall

The cell ‘plasma’ m embrane 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 are 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 that 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 can ‘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).

ORGANELLES & THEIR FUNCTIONS

• Organelles within the cell have specific functions.

-They support the cell and as a whole, maintain its function

-The distribution of organelles varies between cell, depending on their function

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

Replication of parts of the body = depends on genetic codingCodes = blueprint for the manufacture of proteins that form a part of cell structures and tissues, enzymes, hormones, nucleic acids

Genetic codes - contained within the nucleus of the cell embedded within the DNA and RNA complexesProtein synthesis occurs within the cell cytoplasm - you need to

understand this process and this is a part of your study to be discussed during Module 2

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 (protein synthesisis covered in module 2)

They are tiny, and can be found free in the cytoplasm or attached to endoplasmic reticulum

This diagram shows a model of the two subunits that make up a ribosome

A stack of membranous sacs, associated with the ER

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

Essentially packages the products in transport vesicles to transport to somewhere inside or outside the cell.

The Golgi apparatus

MitochondriaOriginated from bacteria-contain their own DNA and self replicate. Essential for effective energy production.

They convert substances like glucose and fats to a form of energy that can be used by the cells (i.e. ATP- this will be discussed later)

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 module 2)

• Without adequate feeding- would wounds heal?

Digest 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

Lysosomes

Peroxisomes

• Peroxisomes are membrane enclosed spherical vesicles that contain several specific enzymes

• Peroxisomes- present in most cells – particularly large and active in the liver (think of a

substance detoxified by the liver……)

• Peroxisomes ‘oxidize’ toxic molecules, removing hydrogen and transferring it to oxygen to form hydrogen peroxide

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…………….

Summary• In this session we reviewed:

1. Levels of organisation

2. Cell Theory

3. Cell structure

4. Organelles and their functions