Download Structure, Function and Homeostasis

Cells
Structure, Function and
Homeostasis
Characteristics of Cells
• Basic unit of life
– anything alive is made of cells
• Plasma membrane (skin) that separates them
from the environment.
• Skeletonsfor protection & support (proteins)
• Move (via proteins)
• Communicate (via hormones)
• Harness & use Energy (produce enzymes, heat)
• Reproduce (maintain & copy blueprint for life)
Cells are small
• 10 – 100µm
• Small to minimize energy
needs…
• But large enough to
house specialized
organelles and to
minimize heat loss
Size determines rate of life
• Large enough to house
organelles needed to
eat, grow, reproduce
• Small enough that
verylittle energy &
time is needed for
transport of nutrients
& waste
Soviet Russia
Simple, Prokaryotic cells
• Lack nuclei (have nucleoid region), few organelles
• Circular DNA (with just 1 copy of each gene)
Bacteria & Archaea - Prokaryotes
• Wildly diverse
– ~ 500 species in your mouth alone
• Abundant (numerous)
– 1012 on your skin; 1014 in G. I. tract; 1 teaspoon
of soil contains billions
• Ubiquitous
– O2-free mud; salt flats; boiling hot springs;
bedrock 1500 m deep; 10 km beneath ocean’s
surface; 0˚- 121˚C
2/3 major evolutionary lineages
Types of Eukaryotic cells
Eukaryotic Animal cell
• Endomembrane System
•
•
•
•
•
•
– Nucleus
– Smooth & Rough Endoplasmic
Reticulum
– Golgi Apparatus
– Lysosomes **
– Plasma membrane
Ribosomes
Peroxisomes
Mitochondria
Centrioles **
Flagellum **
Cytoskeleton
Eukaryotic Plant cell
• Vacuole
• Cloroplasts (&
other plastids:
amyloplasts)
• Cell wall
Nucleus: Control center (brain)
Cytoplasm - organelles,
free proteins, ions (guts)
Cell (plasma) membrane barrier between inside
and outside (skin)
Questions for the cell
• What structure controls which proteins, lipids
& RNA are produced & when?
• Where do cells get Energy? Which structures
harness it?
• What structures move stuff around the cell?
• Where are proteins and lipids built?
• How do cells move molecules in and out?
• How do cells eat, drink & defend themselves?
Nucleus: Control center
• Holds DNA, and
“machinery” for
replicating DNA
and transcribing it
into proteins
• Surrounded by
nuclear envelope
(phospholipid
bilayer)
•Nuclear pores
•Chromatin
•Chromosomes
• Genetic code =
DNA, coiled into
chromosomes
• Chromosomes?
– Hypercoiled
chromatin
• Chromatin?
– DNA coiled
around protein
Where and what is the
cytoplasm?
• Between cell membrane & nuclear
membrane
• Consists of:
– Cytosol: intracellular fluid (mostly H20, ions
& buffering proteins)
– Organelles: structures with specific
functions; suspended in cytosol
– Inclusions: Insoluble material (e.g. lipids)
Ribosomes
• Organ of protein
synthesis
• Made of 2 subunits; each
made of rRNA + protein
• Two varieties
– Free ribosomes: produce
proteins that travel to
nucleus
– Fixed ribosomes: produce
proteins for export to
Endoplasmic Reticulum (ER)
Endoplasmic Reticulum (ER)
•
•
Network of membranes
connected to nuclear
envelope
4 major functions
1. Synthesis (pro, carbs,
lipids)
2. Storage
3. Transport
4. Detoxification
•
Two types
1. Smooth
2. Rough
Smooth ER (SER)
• Why is it called smooth?
• Responsible for the synthesis and
storage of:
– Phospholipids and cholesterol for
maintenance & growth of cellular membranes
(ER, nucleus, Golgi apparatus (GA)) What type of
molecules?
– Steroid hormones: estrogens and androgens
– Triglycerides in liver and fat cells
– Glycogen in skeletal muscle and liver cells
What type of molecules?
Rough ER (RER)
• Workshop
• Site ofprotein
synthesis (it has
fixed ribosomes!!)
Some chemical
modification.
– Polypeptide chains
migrate into cisternae,
assume tertiary
structure + additional
modification
• Ships proteins to GA
via transport vesicles
Golgi Apparatus
• Packing & shipping depot
• Consists of 5-6
flattened membranous
disks (cisternae)
• Functions
– Modifies (adds parts) &
packages secretions
– Renews cell membrane
– Packages special enzymes
Functions of GA
•
Produces 3 type of vesicles:
1. Secretory - exocytosis
2. Membrane renewal – replacement & remodeling
3. Lysosomes - “Primary” contain inactive digestive enzymes
Lysosomes digest!
Show “Lysosomes”
Abnormal lysosomes
• Lack, or have malfunctioning enzymes
– Normal cell products accumulate & stifle
(suffocate) cells
• Tay-Sachs disease
– Lysosomes lack enzymes that break down
lipids in nerve cells
• Pompe’s disease
– Lysosomes lack hydrolytic enzyme that splits
glycogen
The endomembrane system
allows membrane flow
• Phospholipid bilayer is maintained!
• Nuclear envelope  continuous network of SER
& RER  transport vesicles  Golgi Apparatus
 secretory vesicles  cell membrane
Peroxisomes metabolize
dangerous material
• Functions:
– Absorb and breakdown fatty acids and
nucleic acids - produces H2O2 (danger!)
– Convert free radicals to H2O2
– Coverts H2O2 to harmless H2O and O2, using
catalase
• Produced by division of existing
peroxisomes
• Contain digestive enzymes; produced @
free ribosomes
Concept Check
The cell is sometimes described as a protein factory. Using the cell-asfactory analogy, which of the following accurately describes the
functions of the endomembrane system?
a) The ribosomes on the
rough endoplasmic
reticulum are analogous to
a production line in a
factory.
b) The golgi apparatus is
analogous to the packaging
and shipping department.
c) The nucleus is analogous to
management offices.
d) All of the above.
Mitochondria = Powerhouse
Mitochondria harness energy!
• “powerhouse” of the
cell…makes ATP
• Double membrane
• Number per cell
varies with
metabolic activity
(0% volume of RBC, 20%
volume of liver cell)
• Aerobic respiration
• Anaerobic resp.
Chloroplasts make food!
• Photosynthetic
organisms (Autotrophs)
• Sunlight + CO2 + H20 =
sugars
• Stroma: tubules &
membranous disks
• Grana: stacks of disks;
membranes chock full
of chlorophyll, which
traps solar energy
Cell Membrane = Fluid Mosaic
Structure of cell membrane
• Contains lipids, proteins and
carbohydrates
– Lipids
• Phospholipids; Cholesterol; Glycolipids
– Proteins
• Integral; Peripheral
– Carbohydrates
• Form glycocalyx (identity)
Cell Membrane Functions
• Physical isolation - separates inner and
outer environments
• Sensory receptor - receptor proteins
sense changes in external environment
(encrusted with peripheral nerves)
• Regulates exchange with the
environment - membrane channel proteins +
carrier proteins
• Structural support - intercellular protein
attachment