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 – 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.