Download Cell Structure and Function

Endomembrane System
• Endoplasmic Reticulum (ER)
o Rough ER (RER)
• Ribosomes are attached to the cytoplasmic
surface
o Studded appearance
• Ribosomes on the surface RER surface
synthesize proteins
o New polypeptides enter the lumen of the
RER (inside compartment)
o Polypeptides are chemically modified and
folded in the lumen
o Modified proteins are packaged in vesicles
and transported from the RER by budding
Endomembrane System
• Endoplasmic Reticulum (ER)
o Smooth ER (SER)
•
•
•
•
•
Continuous with the RER, but no ribosomes
Synthesis of lipids and steroid hormones
Detoxification of medications and poisons
Alcohol metabolism
Storage of calcium ions
Rough ER
Smooth ER
Fig. 4.14, p. 63
Endomembrane System
• Golgi Apparatus
o Compartment of flattened membrane sacs
o Proteins and lipids from the ER (transported by vesicles) are sorted,
packaged, and tagged so that they end up in the right place
Endomembrane System
• Golgi Apparatus
o Vesicles containing proteins or lipids from the
ER bud off and join the Golgi on the cis side
(near the ER)
• Vesicles fuse with the Golgi membrane
• Contents of the vesicle empty into the Golgi lumen
• Contents are sorted and modified
o Vesicles bud off the trans side (side away from the
ER) to exit the Golgi
• Contain modified and sorted proteins or lipids
• Have a “signal” that tells the cell where the
product needs to be delivered
ROUGH ER
Golgi
SMOOTH ER
GOLGI BODY
Cis side
Lumen
Trans side
budding
vesicle
Endomembrane System
• Lysosomes
• Cell’s “garbage disposal” containing very reactive enzymes
Lysosome
Endomembrane System
• Lysosomes
• Cell’s “garbage disposal” containing very reactive enzymes
• Used to break down waste material and cellular debris
Endomembrane System
• Lysosomes
• Cell’s “garbage disposal” containing very reactive enzymes
• Used by uni-cellular organisms for digestion of food
Endomembrane System
• Lysosomes
• Cell’s “garbage disposal” containing very reactive enzymes
• Used by immune system cells (macrophages) to capture and process
pathogens
Endomembrane System
• Vesicles
o Membrane-bound sacs functioning in storage and transport
• ER  Golgi  cell membrane
o Form when patches of membrane bulge and break away (or bud)
• Vesicles can fuse with membranes and empty their contents to the other side
Endomembrane System
• Vesicles
o Endocytosis
• Bulk movement of materials across the plasma
membrane into the cell
• Pinocytosis
o Nonspecific uptake of small droplets of
extracellular fluid
Endomembrane System
• Vesicles
o Endocytosis
• Phagocytosis
o Cell takes in solid material rather than liquid
o The vesicle fuses with a lysosome to digest the
particles
• Receptor-mediated endocytosis
o A specific receptor protein grabs hold of the
specific solid material to bring it in
Endomembrane System
• Vesicles
o Exocytosis
• Secretory vesicles fuse with the plasma
membrane releasing the molecules to the
outside of the cell
Animation of exocytosis and endocytosis
Endomembrane System
• Vacuoles
o Small vesicles fuse together into larger sacs
o Central Vacuole in plants
• Very large structure
• Contain amino acids, sugars, toxins and ions
• Fluid pressure keeps plant cells firm
Central
Vacuole
Endomembrane System
• Vacuoles
o Contractile vacuole
• Collects and expels excess water
• Used by single-celled protists
Endomembrane System
• Vacuoles
o Food vacuole
• Cell membrane is used to engulf bacteria or other small food
• Used by some single-celled protists
lysosome
Ribosomes
• Assemble amino acids into polypeptides (protein synthesis)
• Found in the cytoplasm or on the rough ER
• Not bound by membranes
• Composed of two subunits
Ribosomes
o Proteins, enzymes, and RNA make up the subunits
Mitochondria
• Produce energy using aerobic respiration
o Oxygen-requiring metabolic pathway that breaks down organic
molecules (food)
• Surrounded by two lipid bilayers
• Envelope
o Outer membrane is smooth
o Inner membrane is highly folded
• More surface area for energy production
• All eukaryotic cells have mitochondria (a few exceptions in Kingdom
Protista)
• Referred to as “powerhouse” or “energy factories” of the
cell
Plastids
• Plastids function in production or storage of
organic molecules
o Chromoplasts
• Make and store pigments
o Responsible for the color in many flowers, leaves, fruits,
and roots
o Amyloplasts
• Store starch grains
• Found in potatoes and other starch-storing plant parts
Plastids
• Chloroplasts
• Make chlorophylls and function in photosynthesis
• Produce energy using photosynthesis
• Pigments capture the sun’s energy which is converted
into chemical energy and organic molecules
• Surrounded by two phospholipid bilayers
(envelope)
• Outer membranes are smooth
• Enclose the stroma (semifluid interior)
• Thylakoid membrane is a third inner membrane
• Continuous compartment folded into disks
• Only found in Plant and Algae cells
Peroxisomes
• Small, round organelles enclosed by a single membrane
• Functions
o Break down fatty acids and amino acids
o Detoxify some poisons
• Alcohol is detoxified by peroxisomes in liver cells
• These chemical reactions produce H2O2
o Which is broken down to water and oxygen
o Reactions are contained in peroxisomes
Cell Surface Specialization
• Cell Wall
o
o
o
o
Surrounds the cell membrane on some cells
Porous structure that protects, supports, and gives shape to the cell
Plants, Fungus, and some Protista have cell walls
Animals do not have cell walls
Cell Surface Specialization
• Extracellular matrix
o Non-living mixture secreted by cells
• Fibrous proteins and polysaccharides
o Supports, anchors, separates, etc.
o Plant cuticle
o Exoskeleton of arthropods
o Bone
Cell Surface Specialization
• Cell junctions
o Connect a cell to other cells and
the environment
• Plasmodesma
o Channel between cell walls of two
adjacent plant cells
o Some send or receive signals
Match the following
Nucleus
Powerhouse
Rough ER
Sort and package
Smooth ER
Chromosomes
Golgi
Organize lipid synthesis
Vesicle
Photosynthesis
Chloroplasts
Cytoskeleton
Mitochondria
Organize polypeptide synthesis
Microtubules
Transport
Summary
• How Cells are Studied
• Comparing Prokaryotic and Eukaryotic Cells
• Eukaryotic Cells
o Plasma membrane, cytoplasm, cytoskeleton, endomembrane
system, ribosomes, mitochondria, chloroplasts, cell surface
NUCLEUS
nuclear envelope
nucleolus
DNA in nucleoplasm
CYTOSKELETON
microtubules
microfilaments
intermediate
filaments
RIBOSOMES
ROUGH ER
MITOCHONDRION
SMOOTH ER
CENTRIOLES
GOLGI BODY
PLASMA
MEMBRANE
b Typical animal cell components.
LYSOSOME
Stepped Art
Fig. 4-19, p. 64
plasma
membrane
nucleus
mitochondria
Fig. 4-14, p. 60
CELL WALL
CHLOROPLAST
CENTRAL
VACUOLE
NUCLEUS
nuclear envelope
nucleolus
DNA in nucleoplasm
CYTOSKELETON
microtubules
microfilaments
intermediate
filaments
(not shown)
RIBOSOMES
ROUGH ER
MITOCHONDRION
SMOOTH ER
PLASMODESMA
GOLGI BODY
a Typical plant cell components.
PLASMA
MEMBRANE
LYSOSOMELIKE VESICLE
cell wall
plasma
membrane
central
vacuole
nucleus
chloroplast
Fig. 4-14, p. 60