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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 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.
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.
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
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