CELLS

Cell – the building blocksThe cell is the basic unit of life; living cells are

made of cells.Cells Tissue Organ System Organism

They are viewed using a microscope.

The Cell TheoryConcept Evidence

1. Living cells are made of cells Observations by microscopists

2. Cells are the smallest unit of life

Discovery of virusesBiochemical investigations of organelles

3. Cells come from pre-existing cells

Pasteur’s observationObservation on the behaviour of cells at division

4. Cells contain a blueprint for growth, development and behaviour

Observations on the behaviour of chromosomes

5. Cells are the site of the chemical reactions of life

Discovery of enzymesDiscovery of biochemical eventsDiscovery of cell ultrastructure

The Discovery of Cell  1590  Hans and Zacharias Jansen constructed the first crude

compound microscope  1665 Robert Hooke looked at a slice of cork under a compound

microscope and discovered the cork was made up of small “boxes” that he named cells

 1680  Anton von Leeuwenhoek looked at blood and pond water under

a microscope.  He saw moving microscopic creatures that he named “Animalcules.”

 1824  Henri Dutrochet came to the conclusion that all living things

are made of cells.  In other words, cells are the “building blocks” of life

The Discovery of Cell continued…  1826  Pierre Turpin observed cell division  1838Matthias Schleiden studied plant tissue under a microscope and

discovered all plants were composed of “cells”  1839Theodor Schwann studied animal tissue under a microscope and

found that animals were also composed of cells  Hugo von Mohl described the process of mitosis in plant cells  1855  Rudolph Virchow stated that all living cells come from other living

cells  1873  Anton Schneider observed chromosomes inside of a cell during cell

division

Relative Sizes of Molecules vis-à-vis Cell Biological Entity

Size

Molecules 1 nm

Cell Membrane thickness

10nm

Virus 100nm

Bacteria 1 um

Cell Organelles

Up to 10um

Cells Up to 100 um

Microscopy and MagnificationMicroscope – an instrument used to see objects that are too

small for the naked eye. Compound Microscopes - are designed with a compound lens

system.

Electron Microscope (EM)– use a beam of highly energetic electrons to examine objects on a very fine scale.

Transmission EM – yields the size, shape and arrangement of the particles which make up the specimen as well as their relationship to each other on the scale of atomic diameters. 

Scanning EM – yields the surface features of an object or "how it looks", its texture; detectable features limited to a few manometers

Magnification - the process of enlarging the size of something, as an optical image.

Magnification = size of image___ size of specimen

Cell Surface Area: Volume RatioSurface area - units squared (m2)Volume – units cubed (m3)

General Principle:As the cell gets bigger in size, the surface

area:volume ratio becomes lesser. The rate of metabolism of a cell is a function of its

mass, whereas the rate of exchange of materials and heat energy that metabolism generates is a function of the cell’s surface area.

rate of metabolism : cell massrate of exchange of materials and heat : cell’s surface

Types of Cells

Types of CellsProkaryote – unicellular organisms whose cell

lacks membrane bound nucleus and organellesex. Bacterial cell

Eukaryote – unicellular to unicellular organisms whose cell contain a membrane bound nucleus and organellesex. Animal and plant cell

N.B. Both unicellular and multicellular organisms can do

the basic life processes.

Prokaryote

Prokaryotic Cell Structure Prokaryotic cells are not as complex as eukaryotic cells. They have no true nucleus as the DNA is not contained within a membrane or separated from the rest of the cell, but is coiled up in a region of the cytoplasm called the nucleoid.

Capsule - Found in some bacterial cells, this additional outer covering protects the cell when it is engulfed by other organisms, assists in retaining moisture, and helps the cell adhere to surfaces and nutrients.

Cell Wall - Outer covering of most cells that protects the bacterial cell and gives it shape.

Cytoplasm - A gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules.

Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.

Pili - Hair-like structures on the surface of the cell that attach to other bacterial cells. Shorter pili called fimbriae help bacteria attach to surfaces.

Flagella - Long, whip-like protrusion that aids in cellular locomotion. Ribosomes - Cell structures responsible for protein production. Plasmids - Gene carrying, circular DNA structures that are not involved in

reproduction. Nucleiod Region - Area of the cytoplasm that contains the single

bacterial DNA molecule.

Eukaryote

Eukaryotic Cell StructureOrganelle Function

NucleusThe “brains” of the cell, the nucleus directs cell activities and contains genetic material called chromosomes made of DNA.

Mitochondria Make energy out of food

Ribosomes Make protein

Golgi Apparatus Make, process and package proteins

Lysosome Contains digestive enzymes to help break food down

Endoplasmic Reticulum

Called the "intracellular highway" because it is for transporting all sorts of items around the cell.

VacuoleUsed for storage, vacuoles usually contain water or food. (Are you are thirsty? Perhaps your vacuoles need some water!)

Plant cells also have:

Chloroplasts Use sunlight to create food by photosynthesis

Cell Wall For support

Characteristic Prokaryotes Eukaryotes

Size of cell Typically 0.2-2.0 m m in diameter Typically 10-100 m m in diameter

Nucleus No nuclear membrane or nucleoli (nucleoid) True nucleus, consisting of nuclear membrane & nucleoli

Membrane-enclosed organelles

Absent Present; examples include lysosomes, Golgi complex, endoplasmic reticulum, mitochondria & chloroplasts

Flagella Consist of two protein building blocks Complex; consist of multiple microtubules

Glycocalyx Present as a capsule or slime layer Present in some cells that lack a cell wall

Cell wall Usually present; chemically complex (typical bacterial cell wall includes peptidoglycan)

When present, chemically simple

Plasma membrane No carbohydrates and generally lacks sterols

Sterols and carbohydrates that serve as receptors present

Cytoplasm No cytosketeton or cytoplasmic streaming Cytoskeleton; cytoplasmic streaming

Ribosomes Smaller size (70S) Larger size (80S); smaller size (70S) in organelles

Chromosome (DNA) arrangement

Single circular chromosome; lacks histones Multiple linear chromosomes with histones

Cell division Binary fission Mitosis

Sexual reproduction No meiosis; transfer of DNA fragments only (conjugation)

Involves meiosis

Eukaryotic and Prokaryotic Cell Structure

Cell Structure Prokaryotic Cell

Typical Animal Eukaryotic Cell

Cell Membrane Yes Yes

Cell Wall Yes No

Centrioles No Yes

Chromosomes One long DNA strand

Many

Cilia or Flagella Yes, simple Yes, complex

Endoplasmic Reticulum No Yes (some exceptions)

Golgi Complex No Yes

Lysosomes No Common

Mitochondria No Yes

Nucleus No Yes

Peroxisomes No Common

Ribosomes Yes Yes