eukaryotic cells. us vs. them -eukaryotes and prokaryotes
TRANSCRIPT
Introducing Eukaryotic Cells
• Eukaryotic (“true nucleus”) cells carry out much of their metabolism inside membrane-enclosed organelles
• Organelle– A structure that carries out a specialized
function within a cell
Animal Cells are Unique
• Animal cells do not have chloroplasts or cell walls.
• They do contain centrioles and may have cilia or flagella.
1.They contain chloroplasts which are the organelles responsible for photosynthesis or the conversion of light energy into chemical energy.
The overall equation for photosynthesis is the reverse of respiration (oxidation of glucose):
light energy 6 CO2 + 6 H2O ----------------> Glucose + 6 O2
Plant Cells are unique in the following respects :
2. In addition to a cell membrane, plant cells are bounded by a rigid cell wall composed mainly of cellulose.
3. Mature plant cells contain a large membrane bounded vacuole mainly used for storage and water balance.
4. Most plant cells contain no centrioles, cilia, or flagella.
The Nucleus
• The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the cytoplasm
• The nuclear envelope controls when DNA is accessed
The Nucleus
Think of the nucleus as the cell’s control center.
Two meters of human DNA fits into a nucleus that’s 0.000005 meters across.
The Nuclear Envelope
• Nuclear envelope– Two lipid bilayers pressed together as a
single membrane surrounding the nucleus–Outer bilayer is continuous with the ER–Nuclear pores allow certain substances
to pass through the membrane
The Nucleoplasm and Nucleolus
• Nucleoplasm– Viscous fluid inside the nuclear envelope, similar
to cytoplasm
• Nucleolus– A dense region in the nucleus where subunits of
ribosomes are assembled from proteins and RNA
The Chromosomes
• Chromatin– All DNA and its associated proteins in the nucleus
• Chromosome– A single DNA molecule with its attached proteins– During cell division, chromosomes condense and
become visible in micrographs– Human body cells have 46 chromosomes
The Endoplasmic Reticulum
• Endoplasmic reticulum (ER) – An extension of the nuclear envelope that forms a
continuous, folded compartment• Two kinds of endoplasmic reticulum– Rough ER (with ribosomes) folds polypeptides into
their tertiary form– Smooth ER (no ribosomes) makes lipids, breaks
down carbohydrates and lipids, detoxifies poisons
Vesicles• Vesicles– Small, membrane-enclosed saclike organelles that store
or transport substances
• Peroxisomes– Vesicles containing enzymes that break down hydrogen
peroxide, alcohol, and other toxins
• Vacuoles– Vesicles for waste disposal
Golgi Bodies and Lysosomes
• Golgi body– A folded membrane containing enzymes that modify
polypeptides and lipids delivered by the ER– Packages finished products in vesicles that carry them
to the plasma membrane or to lysosomes
• Lysosomes– Vesicles containing enzymes that fuse with vacuoles
and digest waste materials
The Lysosome
Cell suicide (suicide is bad for cells, but good for us!)
Recycling cellular components
Functions: Digesting food or cellular invaders
(The lysosome is not found in plant cells)
This bacterium about to be eaten by an immune system cell will spend the last minutes of its existence within a lysosome.
Lysosome Malfunction
• When lysosomes do not work properly, some cellular materials are not properly recycled, which can have devastating results
• Different kinds of molecules are broken down by different lysosomal enzymes– One lysosomal enzyme breaks down gangliosides, a kind of
lipid– Absence of this enzyme results in lipid build up in brain
causing death of cells and ultimately death of the individual (Tay-Sachs disease)
Other Organelles
• Eukaryotic cells make most of their ATP in mitochondria (aka plastid – any organelle containing food or pigment. Chloroplasts are also known as plastids)
• Plastids function in storage and photosynthesis in plants and some types of algae
Mitochondria
• Mitochondrion– Eukaryotic organelle that makes the energy
molecule ATP through aerobic respiration– Contains two membranes, forming inner and
outer compartments; buildup of hydrogen ions in the outer compartment drives ATP synthesis
– Has its own DNA and ribosomes– Resembles bacteria; may have evolved through
endosymbiosis
The Mitochondrion
Think of the mitochondrion as the powerhouse of the cell.
Both plant and animal cells contain many mitochondria.
(Mitochondria is the plural of mitochondrion)
The Mitochondrion
A class of diseases that causes muscle weakness and neurological disorders are due to malfunctioning mitochondria.
Worn out mitochondria may be an important factor in aging.
The ChloroplastThink of the chloroplast as the solar panel of the plant cell.
Only plants have chloroplasts, but animals reap the benefits too.
Plant Organelles
• Chloroplasts–Plastids specialized for photosynthesis–Resemble photosynthetic bacteria;
may have evolved by endosymbiosis