CHAPTER 7A TOUR OF THE CELL

The Cell Theory

• The basic unit of life

• Cells come from cells

• 17th century – cells observed through microscope (CYTOLOGY)

Microscopes provide windows to the world of the cell

Microscopy: History

Simple Compound

Microscopy: History

Microscopy: History

Goals of Microscopy

Produce a magnified image of the specimen (Magnification)

Separate the details in the image (Resolving Power)

Render the details visible to the human eye or camera.

Magnification• Magnification - ratio of an object’s image to its

real size

                                                                                                                     

Onion – 40X Onion – 1000X

Resolving power

Resolving power is a measure of image clarity.

–It is the minimum distance two points can be separated and still viewed as two separate points.– It is determined by the wavelength of light used                                                                                                      

              

0.2m

0.1nm

Enhancing Light Microscope Images

• Electron microscope (EM) -focuses a beam of electrons through the specimen or onto its surface

• Can study only DEAD CELLS!

• Transmission electron microscopes (TEM) are used mainly to study the internal ultrastructure of cells (2D).

Fig. 7.2a (Rabbit Trachea)

• Scanning electron microscopes (SEM) are useful for studying surface structures (3D).

Fig. 7.2b

Gravitational Biology Facility (GBF)

• Cell fractionation - separate the major organelles of the cells so that their individual functions can be studied.

Cell biologists can isolate organelles to study their functions

Fig. 7.3

• Ultracentrifuge- a machine that can spin at up to 130,000 revolutions per minute and apply forces more than 1 million times gravity (1,000,000 g).

1) Homogenization- disrupt the cell and release its contents.

2) Spin homogenate in a centrifuge.

3) Heavier pieces will separate into the pellet while lighter particles remain in the supernatant.

4) Repeat at higher speeds and longer durations- smaller and smaller organelles can be collected in subsequent pellets.

All cells have:

• Plasma membrane.

• Cytoplasm

• Chromosomes

• Genes, DNA

• Ribosomes, (make proteins using the instructions contained in genes)

Prokaryotic and Eukaryotic cells

The prokaryotic cell

The Eukaryotic cell

Prokaryotes• No nucleus, ‘naked’ DNA

• No membrane bound organelles

• Cell wall has peptidoglycan

• Smaller in size (1-10um)

• Nucleus bound by a membrane

• Membrane Bound Organelles

• No peptidolycan in cell wall of plants

• Upto 10 times larger (10- 100um)

• More complex

Eukaryotes

Similarities:-Both have Ribosomes -Are both covered by plasma membrane!-Both have DNA-DNA-> mRNA -> Protein (universal genetic code)

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.7

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.8

• The plasma membrane functions as a selective barrier that allows passage of oxygen, nutrients, and wastes

• Made up of phospholipids and proteins

Nucleus (5 microns)Contains most of the genes

Nuclear Membrane (double) covers it

Pores in Nuclear Membrane (why?)

Nucleolus – rRNA is sythesized here

Chromatin is inside nucleus (DNA+protein)

Chromosomes (46)

NucleusFunction: Stores genes (DNA)

Makes mRNA and other types of RNA

Ribosomes Made up of rRNA and Protein

Located ‘free’ in cytoplasm or in association with ER/ nuclear membrane (‘bound’)

Function – Protein synthesis ‘benches’

Proteins made on Free ribosomes – these proteins stay in cytoplasm

Proteins made on Bound ribosomes – proteins are located in the Plasma Membrane or exported out of the cell

Endomembrane System Nuclear Envelope

Endoplasmic Reticulum

Golgi apparatus (or body)

Lysosomes

Vacoules

Plasma Membrane

Endoplasmic Reticulum Made of sacs - cisternae

2 types: Smooth ER and Rough ER

Smooth ER functions: Lipid synthesis, glucose metabolism, detoxification of drugs (alcohol), muscle contraction

Rough ER functions: Proteins fold in cisternae, some proteins are modified; plasma membrane proteins and phospholipids are synthesized

What cell has a lot of RER?-Cells involved in synthesis of enzymes for digestion ex: pancreasWhat cell has a lot of SER?-Cells involved in detoxification - in a alcoholic!-Cells making steroid hormones!

Transport Vesicles Pinch off from the ER and contain the macromolecules being transported to the Golgi apparatus

Golgi Apparatus Made of sacs – cisternae; cis side- receiving, trans side – news vesicles bud off

Functions: Tags (attaches chemical groups), sorts, and packages macromolecules (warehouse)

Lysosomes

membrane-bounded sac of hydrolytic enzymes that digests macromolecules; low pH (5) inside lysosome protects the cell - how?

Functions:

Phagocytosis-In Amoeba – digestion of food vacoules

Autophagy - recycling of cells own macromolecules (suicide bags)

Destroy bacteria, viruses – in WBC

Vacuoles

Vesicles and vacuoles (larger versions) are membrane-bound sacs with different functions.

Food vacuoles, fuse with lysosomes during phagocytosis

Contractile vacuoles, pump excess water out of the cell (amoeba)

Central vacuoles are found in many mature plant cells – stores water, salts, proteins, defensive compounds, pigments, metabolic byproducts

Mitochondria

Mitochondria and chloroplasts are the main energy transformers of cells

Chloroplast• Found only in

photosynthetic organisms (plants, some primitive eukaryotes)

• Site for photosynthesis (makes glucose)

• Has its own DNA• Has its own ribosomes• Has a double outer

membrane• Is semi-autonomous

• Found in plants and animals• Converts macromolecules

into usable energy – ATP (site for cellular respiration)

• Has its own DNA• Has its own ribosomes• Has a double outer

membrane• Is semi-autonomous

What cell has a lot of Mitochondria?-Cells needing a lot of ATP - heart muscle cell (for pumping), and liver cell (synthesis)

– Peroxisome has catalase that converts H2O2 to water;detoxify alcohol and other harmful compounds

Peroxisomes generate and degrade H2O2

• Network of fibers extending throughout the cytoplasm

Cytoskeleton

• Provides mechanical support and maintains shape

• Provides anchorage for many organelles and enzymes

• Is dynamic - dismantling in one part and reassembling in another to change cell shape.

Movement of cilia, flagella, muscles

Movement of organelles

• 3 main types of fibers in the cytoskeleton: Microtubules, Microfilaments, and Intermediate filaments.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

1) Microtubules – made of tubulin (protein)

• They grow or shrink as more tubulin molecules are added or removed.

• Move chromosomes during cell division

• Guide organelles

• Are part of centrioles – (important to cell division)

• Make up cilia and flagella

Fig. 7.26 The shape of the microvilli in this intestinal cell are supported by microfilaments, anchored to a network of intermediate filaments.

2) Microfilaments (Actin)

-Support-Muscle contraction-Amoeboid movement-Cytoplasmic streaming

3) Intermediary filaments

- cell shape, organelle location

• Microfibrils of cellulose embedded in a matrix of proteins and other polysaccharides.

Plant cells are encased by cell walls

Extracellular matrix (ECM) of animal cells

COLLAGEN-glycoprotein

• Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact.

• Plant cells are perforated with plasmodesmata, channels allowing cysotol to pass between cells.

Intracellular junctions help integrate cells

• Animal Cells:

Fig. 7.30

– Macrophages use actin filaments to move and extend pseudopodia, capturing their prey, bacteria.

– Food vacuoles are digested by lysosomes, a product of the endomembrane system of ER and Golgi.

A cell is a living unit greater than the sum of its parts

• The enzymes of the lysosomes and proteins of the cytoskeleton are synthesized at the ribosomes.

• The information for these proteins comes from genetic messages sent by DNA in the nucleus.

• All of these processes require energy in the form of ATP, most of which is supplied by the mitochondria.

• A cell is a living unit greater than the sum of its parts.

Fig. 7.31