Transcript Chapter 3: Cells

Chapter 3: Cells
A. Cells are the units of life
• All organisms consist of
cells
• Cells are the smallest unit of
life that can function
independently
• 1660 – Robert Hooke first
person to see outlines of
cells (in cork)
• 1673 – Antony van
Leeuwenhoek improved
lenses and drew
observations
• 1830’s – Robert Brown
identified the nucleus
• Cell theory (est. ~ 1839)
– 2 Main tenets (ideas)
• All organisms are made of one or more cells
• The Cell is the fundamental unit of life
• Ideas developed by Schleiden and Schwann
– 3rd Main tenet
• All cells come from preexisting cells
– Contradicts the idea of spontaneous generation
• This idea was added in 1855 by Virchow
• Microscopes are used to study cells
– Light microscopes
• Compound light microscope - glass lenses focus
visible light, 0.2 µm resolution
• Confocal microscope – enhanced resolution using
white or laser light
– Electron microscopes – greater magnification and
better resolution but specimen must be dead
• Transmission Electron Microscope (TEM) – uses beam of
electrons focused by magnetic field
• Scanning Electron Microscope (SEM) – scans beam of
electrons over metal coated specimen
– Scanning probe microscope – probe moves over
surface giving exquisite detail
• Features common to all cells
– Genetic information, DNA
– Proteins carry out cell’s work
– RNA participates in producing proteins
– Ribosomes manufacture proteins
– Cytoplasm
– Cell membrane
• Complex cells also have organelles –
compartments for specialized functions
• Surface area to volume
– All cells are small
– Require large surface area
– Surface area limitation on size of cell
– May be avoided through
• Flattened shape
• Fingerlike extensions
• Specialized organelles to improve
efficiency (explains animal and plant cells
being larger than bacterial cells)
– Vacuoles in plant cells, etc.
B. Cell membrane
(separating the cell from the external environment and So much more!)
• Composition of the cell membrane:
– Made of lipids and proteins
– Phospholipid
• Glycerol and a phosphate group form head, 2 fatty
acids form the tails
• Head is hydrophilic, tails are hydrophobic
• Together, phospholipids spontaneously form
phospholipid bilayer, like a defense move for the
tails!
– Fluid mosaic – proteins and phospholipids
free to move laterally within the bilayer
– Proteins in the cell membrane:
• Transport proteins
• Enzymes
• Recognition proteins
• Adhesion proteins
• Receptor proteins
Functions of the Cell Membrane:
• Signal transduction
– A cell receives an
external “message” and
converts it into an internal
signal
– Receptor proteins bind to
stimulus molecule, first
messenger
– Triggers chemical
reaction whose product is
second messenger
– Second messenger
provokes cell’s response
– activating particular
genes or enzymes
C. Different cell types
• Prokaryote – simplest and most ancient
forms of life whose cells lack organelles
• Eukaryotes – cells contain organelles
• 3 domains of life
– Bacteria – prokaryote
– Archaea – prokaryote
– Eukarya – eukaryote
C. Different cell types
• Domain Bacteria
– Lack membrane bound nuclei
– 1 circular DNA molecule found in
nucleoid
– Rigid cell wall in most – provides
protection and shape
– Some have capsule and flagella
• Domain Archaea
– Resemble bacteria superficially
only
– Phospholipids, cell walls, and
flagella unique
– Some are “extremophiles”
• Burning Question: What IS the smallest
certifiable living organism? See p. 59!
C. Different cell types
• Domain Eukarya
– Huge diversity
– Larger than prokaryotes
– Internal membranes create internal
compartments called organelles that are
specialized for specific tasks in the cell
– Endosymbiosis theory – maybe ancient organism
engulfed another organism and rather than eating it, it
stayed as a partner (supported by mitochondria and
chloroplasts)
– 2 Major groups of eukaryotic cells based on
structure and functions: animal & plant cells
D. Eukaryotic organelles
• Organelles carry out coordinated interactions to
meet the needs of an organism: Ex: Milk
D. Eukaryotic organelles
• Nucleus
– Contains DNA – information specifying “recipe” for
every protein a cell can make
– Nuclear pores are holes in the nuclear envelope
surrounding the nucleus, lets RNA and other
substances through
– Nucleolus - dark core in middle of nucleus; assembles
ribosomes
• Cytoplasm
– Watery-jelloish soup
of dissolved substances,
organelles and cytoskeleton
D. Eukaryotic organelles
• Ribsomes
– Site of protein synthesis
– Found lose in cytoplasm or
attached to ER
• Endoplasmic Reticulum
– Originates at nuclear
membrane and winds
throughout the cell
– 2 types:
• Rough ER – studded with
ribosomes making proteins
destined for secretion (like milk)
– Proteins folded and modified
• Smooth ER – synthesizes lipids,
detoxifies drugs and poisons
• Lipids and proteins made by ER
exit in vesicles
D. Eukaryotic organelles
• Golgi apparatus
– Processing center for
vesicle contents
– Proteins complete
intricate folding and
become functional
– Some proteins will
become membrane
surface proteins
– Others packaged for
secretion from the cell
D. Eukaryotic organelles
• Lysosomes
– Contain enzymes that lyse substrates
– Specific pH inside lysosome prevents enzymes from
damaging cell
• Vacuoles
– Found in plants
– Enzymes degrade and recycle materials
– Important in growth and maintaining rigidity
• Peroxisomes
– Dispose of toxic substances
– Some reactions produce hydrogen peroxide (H2O2)
– Enzyme produces harmless water molecules
D. Eukaryotic organelles
• Chloroplasts
–
–
–
–
–
Found in plant cells
Site of photosynthesis
Uses energy from sunlight to produce glucose
Occurs specifically in thylakoids
Endosymbiosis theory support – has its own DNA
D. Eukaryotic organelles
• Mitochondria
– Cellular respiration extracts energy from food
– Cristae – internal folds; contain enzymes for cellular
respiration
– Also contains its own DNA
• Always inherited from mother
in humans
http://www.pbs.org/wgbh/nova/neanderthals/mtdna.html
D. Eukaryotic organelles
Cytoskeleton
• 3 major
components
distinguished by
protein type,
diameter, and
aggregation
– Microtubules
– Microfilaments
– Intermediate
filaments
D. Eukaryotic organelles
• Microtubule
– Made of Tubulin protein
– Forms very small hollow
tubes
– Can change length of
tube by adding or
removing tubulin
molecules
– “Trackway” within cell for
many cellular movements
– Cilia – short, many
– Flagella – long, few
D. Eukaryotic organelles
• Microfilaments
– Actin
– Long, very thin rods
– Machinery to move
• Intermediate filaments
– (10 nm) diameter is intermediate
– Made of different proteins in different
specialized cell types
– Internal scaffold for cell
E. Cells adhere and communicate
• Cell walls
– Surround cell
membrane of nearly all
bacteria, archaea,
fungi, algae, and plants
– Not just a barrier
– Built of different
components
– Plasmodesmata
connect adjacent cells
– (like little bridges between cells)
• Animal cell junctions
– Animal cells lack cell
walls
– Secrete complex
extracellular matrix
– Intercellular junctions
1. Tight junctions form
impermeable barriers
2. Anchoring or adhering
junctions connect cells
by linking intermediate
filaments
3. Gap junctions link
cytoplasm of adjacent
cells
http://www.cellsalive.com/cells/3dcell.htm
http://learn.genetics.utah.edu/content/begin/cells/insideacell/
http://learn.genetics.utah.edu/content/begin/cells/scale/
http://www.wisc-online.com/objects/index_tj.asp?objID=ap11604