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Compartmentalization (Organelles)
EK 2B3: Eukaryotic cells maintain internal membranes that partition the cell into specialized regionsEK 4A2: The structure and function of subcellular components, and their interactions, provide
essential cellular processesEK 4B2: Cooperative interactions within organisms promote efficiency I the use of energy and matter
Prokaryotic vs Eukaryotic
- Bacteria and Archaea
- Cell wall made of - DNA in cytoplasm -
circular- Smaller
- Plasma membrane- Chromosomes- Ribosomes- cytoplasm
- Protists, Fungi, Plant, animal cells
- DNA in nucleus - linear- Larger- Membrane bound
organelles (nucleus, ER, Golgi, Mitochondria, Chloroplast (plant cells only), Lysosomes( animal cells only)
Prokaryotic Eukaryotic
Both
Compartmentalization• Breaking the cell into specialized areas• Benefits:• Increase surface area for reactions to take place• Minimizing competing interactions; provide different local environments that facilitate
specific metabolic functions; incompatible processes can go on simultaneously inside a single cell (cellular respiration and photosynthesis same time in different areas)
• Examples:• Nuclear envelope• Endoplasmic reticulum• Golgi• Mitochondria• Chloroplasts
The Nucleus: Information Central
• Contains MOST of the genes in eukaryotic cells (some genes are located in mitochondria and chloroplast)• Nuclear envelope: double membrane that surrounds the nucleus,
contains proteins called pore complex that regulate entry and exit or proteins and RNAs• Contains a specific number of chromosomes based on the species
(humans = 46; flies = 8); remember sex cells (sperm and egg) contain ½ the number of chromosomes (humans = 23; flies = 8)• Nucleus directs protein synthesis by synthesizing messenger RNA (mRNA)• Nucleolus is also located inside the nucleus
The nucleus and its envelope
NucleolusNucleus
Rough ER
Nuclear lamina (TEM)
Close-up of nuclear envelope
1 µm
1 µm
0.25 µm
Ribosome
Pore complex
Nuclear pore
Outer membraneInner membrane
Nuclear envelope:
Chromatin
Surface ofnuclear envelope
Pore complexes (TEM)
Nucleolus
•Synthesizes rRNA (ribosomal RNA) from instructions in the DNA. •Proteins imported from the cytoplasm are assembled with rRNA into large and small ribosomal subunits•Subunits then exit the nucleus through the nuclear pores to the cytoplasm where a large and small subunit can assemble into a ribosome
Ribosomes• Made of two subunits (one small and one large) – subunits are constructed of
proteins and rRNAs –made in nucleolus of eukaryotic cells• Brings tRNA anticodons and mRNA codons together during protein synthesis• Large and small subunits join to form a functional ribosomes only when they
attach to an mRNA molecule• Because most cells contain thousands of ribosomes, rRNA is the most
abundant type of cellular RNA• Eukaryotic ribosomes are slightly larger and differ somewhat from bacterial
ribosomes in their molecular composition• Differences allow allow certain antibiotic drugs to inactive bacterial ribosomes without
inhibiting the ability of eukaryotic ribosomes to make proteins
RibosomesCytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large subunit
Small subunit
Diagram of a ribosomeTEM showing ER and ribosomes
0.5 µm
Ribosomes – more details• Ribosomes contain a binding site for mRNA• Also contain three binding sites for tRNA: • P site (peptideyl-binding site) – holds the tRNA carrying the growing polypetide chain• A site (aminoacyl-tRNA site) – holds the tRNA carrying the next amino acid to be added
to the chain• E site (exit site) – discharged tRNA
• Ribosome hold mRNA and tRNA in close proximity and positions the new amino acid to the carboxyl end of the growing protein• Recall the direction in which amino acids are added is ALWAYS carboxyl to amino end
• As the polypeptide grows it exits the large subunit through the exit tunnel• When complete the protein is released to the cytosol if the protein is
detached/or is inserted into the ER if attached
tRNA carries amino acids to mRNA.
tRNA anticodon pairs with mRNA codon Polypeptide
Ribosome
Aminoacids
tRNA withamino acidattached
tRNA
Anticodon
Trp
Phe Gly
Codons 35
mRNA
P site (Peptidyl-tRNAbinding site) A site (Aminoacyl-
tRNA binding site) E site(Exit site)
mRNAbinding site
Largesubunit
Smallsubunit
Ribosome model showing binding sites.
Next amino acidto be added topolypeptide chain
Amino end Growing polypeptide
mRNAtRNA
E P A
E
Codons
Ribosome model with mRNA and tRNA.
5
3
Endomembrane System
• Includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, various vacuoles, and plasma membrane (not really endo – but is it attached)
The Endomembrane System
Smooth ER
Nucleus
Rough ER
Plasma membrane
cis Golgi
trans Golgi
Endomembrane System• Includes nuclear
envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, various vacuoles, and plasma membrane (not really endo – but is it attached)
Endoplasmic Reticulum
• Two different types:• Smooth:
• Synthesis of lipids (oils, phospholipids, steroids)• Stores calcium ions – muscle cells• Detoxify drugs and poisons
• Increases tolerance to drugs = higher dose required to work• Increase smooth ER due to drug abuse can also lead to decrease effectiveness of certain
antibiotics and other useful drugs
• Rough:• Transports proteins to Golgi body once ribosome makes protein; keeps proteins made on
ER separate from proteins made in cytoplasm
Golgi Complex
• Think of it as UPS• Modifies, sorts, packages, ships macromolecules to where they
are needed in the cell.
Mitochondria
Free ribosomesin the mitochondrial matrix
Intermembrane space
Outer membrane
Inner membrane
Cristae
Matrix
0.1 µm
• Site of cellular respiration
• Enclosed by two membranes with embedded proteins that aid with cellular respiration
• Membrane proteins are made by ribosomes in the cytoplasm of the cell (instructions to make these proteins are found in the nucleus of the cell) AND by ribosomes found inside the mitochondria (instructions to make these proteins are found in the mitochondrial DNA)
• Outer membrane is smooth; Inner membrane is folded to increase surface area = increases the amount of ATP that can be created
• Intermembrane space: narrow region between the inner and outer membranes
• Mitochondrial matrix: contains enzymes, mitochondrial DNA and ribosomes
Chloroplast• Site of photosynthesis
• Similar to mitochondria – proteins embedded in chloroplast aid photosynthesis and are made by the ribosomes in the cytoplasm of the cell and by the ribosomes found in chloroplast
• Membranes of the chloroplast separate it into three different compartments:• Intermembrane space: two membranes separated by a very narrow space• Thylakoid: contains chlorophyll (green pigment that captures energy from sunlight); location of light reaction
of photosynthesis • Stroma: contains chloroplast DNA and ribosomes as well as enzymes to aid in photosynthesis; location of the
dark reaction of photosynthesis
Ribosomes
Thylakoid
Stroma
Granum
Inner and outer membranes
1 µm
Lysosomes
• Uses hydrolytic enzymes to digest macromolecules• Made by the rough ER and then transferred to the Golgi apparatus for
further processing• Carry out intracellular digestion in a variety of circumstances• Ex: Fuse with food vacuole to digest macromolecules/macrophage (type of
white blood cell) engulf and destroy bacteria with help of lysosomes
• Compartmentalization – enzymes inside lysosomes are dangerous to other parts of the cell – by keeping them separate they can do their job without harming the cell
Nucleus 1 µm
Lysosome
Digestiveenzymes
Lysosome
Plasmamembrane
Food vacuole
(a) Phagocytosis :engulfs
Digestion
(b) Autophagy : recycles
Peroxisome
Vesicle
Lysosome
Mitochondrion
Peroxisomefragment
Mitochondrionfragment
Vesicle containingtwo damaged organelles
1 µm
Digestion
Lysosomes
Vacuole
• Membrane-bound vesicles whose functions vary in different kinds of cells• Food vacuoles – form by phagocytosis• Contractile vacuoles – pump excess water out of cell to maintain
osmoregulation• Carry out hydrolysis in plant and fungi since they lack lysosomes• Large Central Vacuole in plant cells:
• Storage (water, inorganic ions)• Disposal of metabolic by-products that would endanger cell if in high concentrations in
the cytoplasm• Poisons or unpalatable chemicals for animals (prevent being eatten)