Chapter 4 – A Tour of the Cell

And comparison to viruses

Intro

Intro

Intro

Intro

Intro

State Standards

Standard 1.c. – Prokaryotic cells, eukaryotic cells (including those from plant and animals), and viruses differ in complexity and general structureStandard 1.e. – The endoplasmic reticulum and Golgi apparatus play a role in the secretion of proteins

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The Microscopic World of Cells

• Organisms are either:

– Single-celled, such as most bacteria and protists

– Multicelled, such as plants, animals, and most fungi

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

The Microscopic World of Cells• The human body is made up of trillions of cells many of which are

specialized

– Muscle cells, Nerve cells, & blood cells…

The Cell Theory• Cells were first discovered in 1665 by Robert Hooke.• The accumulation of scientific evidence led to the cell theory

- All living things are composed of one or more cells- All cells are formed from previously existing cells

Microscopes provide windows to the world of the cell

The Light MicroscopeLight passes through the specimenLenses enlarge, or magnify, the imageMagnification – the increase in the specimen’s apparent sizeResolving power – the ability to show 2 objects as being separate

Microscopes provide windows to the world of the cell

The Electron MicroscopeUses a beam of electronsResolving power is higher than the light microscopeCan magnify up to 100,000X

Microscopes provide windows to the world of the cell

Scanning Electron Microscope (SEM)Used to study the details of the surface of the cellProduces a 3D imageUsed to study cell and organelle surfaces

Microscopes provide windows to the world of the cell

Transmission Electron Microscope (TEM)An electron beam is aimed through a thin sectionUsed to explore the internal structures of the cell

The Two Major Categories of Cells

The Two Major Categories of Cells• There are 2 major categories of cells

- Prokaryotic cells- Eukaryotic cells

• Both cells- Are surrounded by a plasma membrane- Consist of cytoplasm and organelles and contain DNA

• Prokaryotic and eukaryotic cells differ in several ways

The Size of CellsMost cells are 10-

100 micrometers in size

Cell size and shape are related to their function

Ex: red blood cells, nerve cells, eggs

The Size of Cells• The lower limit of cell size is determined by the

fact that a cell must be large enough to house the parts (DNA, organelles) it needs to survive and reproduce.

• The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes.

Prokaryotic Cells• Smaller than eukaryotic

cells (2-8 um)• Enclosed by a plasma

membrane that is usually surrounded by a rigid cell wall

• The cell wall may be covered by a sticky capsule

• DNA is found inside the cell but it is not housed in a nucleus

• Ribosomes (70S) are present

• Internal structures surrounded by membranes are not present

Structures of the Prokaryotic CellNucleoid region – area where DNA is coiled in the cytoplasm. DNA is in direct contact with the rest of the cellPlasmid – smaller circular DNA molecules

Ribosomes – where proteins are madePlasma membrane – encloses the cytoplasm of the prokaryotic cell

Structures of the Prokaryotic CellCell wall – rigid, composed of lipids, carbohydrates and protein. Protects the cell and maintains its shape

•Cell Wall components determine if bacteria is classified as• gram positive (+)• or gram negative (-)..In general more toxic and

resistant to antibiotics

http://www.bio.upenn.edu/computing/media/Instructional.Stain.Gram.php

Structures of the Prokaryotic Cell

Capsule – sticky outer coat that surrounds some prokaryotes. Protects the cell surface. Helps bacteria attach to surfacesPili – short surface projections found in some prokaryotes. Helps attach bacteria to surfacesFlagella – long whiplike extensions found in some prokaryotes. Propel cell through liquid environments

The Role of Bacteria in the Nitrogen Cycle

Eukaryotic CellsLarger than

prokaryotic cells (10-100 um)

More complex in structure

DNA housed in the nucleus

Ribosomes (80S)

Membrane bound organelles

Comparing Animal and Plant CellsAnimal cells

contain centrioles, lysosomes, flagella

Plant cells contain a central vacuole, cell wall, chloroplasts

Comparing Eukaryotic and Prokaryotic Cells-Prokaryotes Eukaryotes

Differences Differences

Commonalities

Comparing Eukaryotic and Prokaryotic Cells- Differences in parallel statements

Prokaryotic CellsDate back at least 3.5 BYAEx include: Bacteria & ArchaeabacteriaSimpler Structure (all single celled organisms)

Naked DNA (not wrapped around histone proteins)

Circular ChromosomesDNA in cytoplasm (nucleoid

region)70S ribosomesNo internal membrane

compartments (no membrane bound organelles)-ex: no mitochondria, no Rough ER

Eukaryotic CellsDescended from ancient prokaryotes 2.1 BYAEx organisms: plants, animals, fungi, protistsMore Complex Structure (mostly multicellular organisms but some single celled organism)

DNA associated with histone proteins Chromosomes linear

DNA separated from cytoplasm (in nucleus)

80S ribosomesInternal membrane compartments

(membrane bound organelles) –ex: yup mitochondria and Rough ER

Comparing Eukaryotic and Prokaryotic Cells-

Commonalities: Prokaryotes & EukaryotesSmallest units of Life (therefore has the characteristics of life Chapter 1!)

Requires energy (to run metabolic reactions of life)Grows and developsIndependently reproduce

DNA stores genetic informationCan evolve over generations

Order: internal organizationResponds to environmental stimuli

Ribosomes build proteins for the cellsContains plasma membrane to regulate what enters and leaves the cellFilled with cytosol (fluid)