Download Bio1A Unit 1-3 The Cell Notes File

The Cell
Organelles & Their Functions
Nucleus
Ribosomes
Lysosome
Peroxisome
Mitochondria
Plastids - Chloroplasts
Cytoskeleton
Extracellular Matrix
Protein Trafficking
Membranes
Membrane fluidity
Membrane Proteins
The Cell
Major Features
1. Membrane – compartmentalization
• Separates inside and outside
• But there is flow in and out
 Material
 Communication
2. Cytosol – semifluid substance
3. Genetic Material: i.e.- DNA
• Directs cells activity
• Allows reproduction
4. Ribosomes – Protein production
Prokaryotic
vs
no nucleus
Single circular DNA / chromosome
No membrane bound organelles
Eukaryotic
Eukaryotes – nucleus contains DNA
Linear pieces of DNA / chromosomes
Membrane bound organelles
Organelles
Nucleus
•Contains most of the Cell’s DNA (as chromatin)
•Nuclear pores for transport
Pore proteins determine what goes in and out
•Continuous with ER
Ribosome – NOT (technically) an organelle
Function - Protein Translation : RNA  Protein
Location - Free floating in cytoplasm or
bound to endoplasmic reticulum
Stucture - 2 multi-complex proteins composed of protein and rRNA
named according to relative size (small and large).
Endoplasmic Reticulum (ER)
Smooth ER –
Lipid biosynthesis – ex: steroids, Fats
Carbohydrate metabolism – breakdown of polysaccharides
Detoxification of drugs
NOT protein synthesis – no ribosomes
Rough ER – rough due to presence of ribosomes
1. Protein synthesis
2. Protein modifications
3. Glycosylation  Carbohydrates (CH2O groups) are attached to some proteins
4. Transferred to Golgi through transport vesicles
(no glycosylation = stays in ER)
Golgi apparatus - Protein Transport / Protein Modification
•
•
•
Phosphorylation
 lysosome
Glycosylation
deglycosylation
Modification determines
final destination
Lysosome - Digestive organelle
•
•
pH 4-5 (required for enzyme function)
Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids
Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole
A lysosome fuses with the food vacuole and digests the molecules
Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a
process called autophagy
Peroxisomes: Oxidation
• Peroxisomes are specialized metabolic compartments bounded by a single membrane
• Peroxisomes produce hydrogen peroxide and convert it to water
• Oxygen is used to break down different types of molecules
Mitochondria and chloroplasts change energy from one form to another
– Are not part of the endomembrane system
– Have a double membrane
– Contain their own circular DNA & ribosomes (small) ~20% of protein made inside
• Mitochondria (plants and animals) are the sites of cellular respiration, a metabolic process
that generates ATP
• Chloroplasts (plants and algae) are the sites of photosynthesis
- Part of a subcategory of plant/algae organelle called plastids
Vacuole – plant
•Large storage vesicle
cytoskeleton
• Fiber network throughout the cytoplasm
• Organizes cell’s structures and activities, anchoring many organelles
– support the cell and maintain its shape
– interacts with motor proteins to produce motility
I. Microtubules - Shaping the cell
• Thickest
• Guiding movement of organelles
• Separating chromosomes during cell division
I. Microfilaments – propulsion
• control the beating of cilia and flagella, locomotor
appendages of some cells
• Cilia and flagella differ in their beating patterns
II. Intermediate filaments: Actin – cellular motility
• Thinnest
• built as a twisted double chain of actin subunits
• structural role - to bear tension, resisting pulling forces
within the cell
The Extracellular Matrix (ECM)
• Animal cells lack cell walls but are covered
by an elaborate extracellular matrix (ECM)
• made of glycoproteins such as collagen
(fibrous), proteoglycans, and fibronectin
• ECM proteins bind and anchor, and
transmit messages
Protein trafficking
Post-Translational Import - Proteins made on free ribosomes
Final Destinations  cytosol, mitochondria & chloroplast, peroxisomes, nucleus (usually)
Requires a transport protein which targets:
N-terminal (usually) targeting signal sequence of peptide
Some have names. Examples:
• Nucleus – Nuclear Localization Signal (NLS)
Importin – protein that transports NLS tagged proteins
• Peroxisomal Targeting Signal
CO-Translational Import - Proteins made on bound ribosomes / Rough ER
Final Destinations  ER, Golgi, lysosome, nuclear membrane, membrane, extracellular
Targets membranes  called endomembrane system
Amino acid sequences are targets for
• directing translating ribosome to bind to ER  rough ER
• Are targets for protein modifications in ER or golgi
Protein modification
In ER
 Glycosylation: Carbohydrates (CH2O groups) are attached to some proteins
 Glycosylation causes transport to Golgi through transport vesicles
(no glycosylation = stays in ER)
In golgi
 Further modification determines final location
Plasma Membrane
• the boundary that separates the living cell from its surroundings
• exhibits selective permeability, allowing some substances to cross it more
easily than others
• Basis for permeability is the hydrophobic nature of the tails of phospholipids
- Lipid bilayer
- Naturally forms do to
hydrophillic interaction of the
heads which must face both
outward and inward to the water
environment both outside and
inside the cell
Fluid Mosaic Model
• The lack of even weak hydrogen bonding
results in a fluid membrane (see video)
• The plasma membrane is a collage spotted
with many different proteins (mosaic)
~45% protein 45% phospholipid 10%
other
• Proteins determine most of the cell’s function
Cholesterol stabilizes membranes
@ high temp – slows fluidity
@ low temp – makes more fluid
Membrane Proteins Characteristics
• Peripheral – bound (loosely) to surface
• Integral = transmembrane proteins (tightly bound)
 hydrophobic regions - stretches of nonpolar
amino acids, often coiled into alpha helices