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Topic 2.3: Eukaryotic Cells
IB Biology HL
E. McIntyre
Cytoplasm (cytosol): a cell's inner space
cytosol
Cytosol: large fluid-filled space (mostly water + proteins that control most of the cell metabolisms): glycolysis, transcription
factors, intracellular receptors etc.
Plasma membrane
Organelles
• Nucleus• Protein production machine: the ribosomes• Mitochondria and Chloroplasts• Endoplasmic Reticulum and the Golgi
apparatus (we don’t say ‘Golgi body’ in IB)
• Lysosomes• Adapted and/or specialized for carrying out
one or more vital functions
Reminder! Membrane-bound organelles are only found in eukaryotes.
Nucleus: a cell's centerFunction of the nucleus:• Stores the chromosomes
(genetic material) Note: Two kinds of genetic material:– deoxyribonucleic acid
(DNA)– ribonucleic acid (RNA)
• Keeps the DNA molecules separated from metabolic machinery of cytoplasm.
• Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells
• DNA replication and synthesis of messenger RNA (mRNA). The mRNA is allowed to leave the nucleus. It is read by the ribosomes during protein synthesis.
...Nucleus: a cell's center
Nucleolus
• Dense mass of material in nucleus
• Cluster of DNA and proteins
• Subunits must pass through nuclear pores to reach cytoplasm
• production of ribosomes in nucleolus
• Two outer membranes (lipid bilayers)
• Pores span bilayer and controls what enters/leaves nucleus.
• Much more detail to follow!
Nuclear Membrane (Envelope)
Chromatin
• Cell’s collection of DNA and associated proteins• A chromosome is one DNA molecule and its
associated proteins• Appearance changes as cell divides
FUNCTION:
• With the help of tRNA, ribosomes use information in mRNA to assemble proteins
• small semi-spherical, black dots
• some are free in cytoplasm (cytoplasmic ribosomes), others are attached to the ER (ER ribosomes)
Ribosomes
STRUCTURE
• ER is a continuation of the outer nuclear membrane.
• Two types: Smooth and Rough. (Rough ER has ribosomes on it)
• Network of membrane that connects nuclear envelope to the cell membrane
Endoplasmic Reticulum (ER)
FUNCTION:
• Smooth ER (no ribrosomes): responsible for lipid and membrane protein modifications). In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs
• E.g., in liver, metabolizes alcohol and barbiturates; in testes and ovaries, synthesizes sex steroids; etc.
• Rough ER (has ribosomes on it) responsible for the synthesis of other proteins). The ribosomes assemble the proteins within the rough ER. Once assembled, the proteins pinch off the ER and are released in a vesicle.
Endoplasmic Reticulum
Endoplasmic Reticulum (ER)
…Endoplasmic Reticulum (ER)
FUNCTION:
• processes, packages, and, secretes cell products (lipids & proteins)
• Put finishing touches on proteins and lipids that arrive from ER
• Package finished material for shipment to final destinations. (Exocytosis)
• Material arrives and leaves in vesicles
Golgi Body (Golgi Apparatus)
Golgi Apparatus
…Golgi Body (Golgi Apparatus)
STRUCTURE
• Double membrane. Inner membrane is folded for greater surface area. Folds are called cristae.
• Interior is called the matrix.
• Contain their own genome (distinct from nuclear genome)
• Self-replicating
FUNCTION
• ‘burns’ food, i.e. glucose to release energy. Energy is used to make ATP. ATP is a high-energy molecule that can be directly used by the cell.
Mitochondria
The “powerhouse” of the cell
…Mitochondria
TEM of Mitochondria
STRUCTURE• Formed by Golgi bodies• Bound by a single membrane
FUNCTIONS• Digests the food particles inside the cell with help of enzymes. These enzymes
work at low pH.• Involved in autolysis (suicide of cell)• Digest foreign bacteria that invade a cell• Recycling of membrane components• Repair damage to plasma membrane
Lysosomes
lysosomes McGraw Hill
Lysosomes
• Made by Golgi
• Surrounded by a single membrane
• Get rid of toxic substances
• Many in the liver/ brain
lysosome
Peroxisomes
FUNCTION:
• maintains the shape of a plant cell
• found in plants, some fungi, some protists
• In plants, cell walls are made of a polysaccharide called cellulose.
• Structural component that wraps around the plasma membrane
Cell Wall
…Cell Wall
FUNCTION:
• Photosynthesis: converts sunlight, carbon dioxide, and water into sugar (makes food for plants)
Chloroplasts
• A large membrane bound sac
FUNCTION:• storage area for proteins and
water• Maintain structure in plant cells by means of turgor pressure
Vacuole
1.3 Eukaryotic Cells2.3.5 Describe three differences between plant and animal cells.
Carbohydrates stored as starch.
Carbohydrates stored as glycogen.
Stores large amounts of liquid (juice). Larger size of cell.
Central Vacuole
XDoes not store large amounts of liquid. Smaller size of cell.
Rigid, cannot easily change shape.
Cell WallXFlexible, can easily change shape.
Can produce its own food.
ChloroplastXCannot produce its own food
Plant CellsStructureAnimal Cells
• very complex and dynamic cell component!
• organizes and maintains the cell's shape (e.g. epithelial cells of the gut)
• anchors the organelles in place
• helps during the uptake of external material (endocytosis)
• involvement in cell movement
• growth
Cytoskeleton: a cell's scaffold
microtubules microfilamentsintermediate filaments
tubulin actin keratin family
All help maintain cell shape
Cilia, flagellaChromosome movementOrganelle movement
Cytoplasmic streamingPseudopodiaCell division
Nuclear laminaAnchorage of nucleus and some other organelles
...Cytoskeleton
...Cytoskeleton
...Cytoskeleton
Molecular motors
...Cytoskeleton
Macrophage attacks bacteriaMicrofilaments (actin) allow formation of pseudopods
...Cytoskeleton
Striated Muscle
...Cytoskeleton
Centrosome: Made up of centriole pairs
...Cytoskeleton
2.3.4 Compare prokaryotic and eukaryotic cells.
• Prokaryotic cells have naked DNA which is found in the cytoplasm in a region named the nucleoid. On the other hand, eukaryotes have chromosomes that are made up of DNA and protein. These chromosomes are found in the nucleus enclosed in a nuclear envelope.
• Prokaryotes do not have any mitochondria whereas eukaryotes do. Prokaryotes make use of their cell surface membrane and mesosomes instead.
• Prokaryotes have small ribosomes (70S) compared to eukaryotes which have large ribosomes (80S).
• In prokaryotes there are either no organelles bounded by a single membrane in comparison to eukaryotes which have many of them including the Golgi apparatus and the endoplasmic reticulum.