Eukaryotic Cells

Us vs. Them -Eukaryotes and Prokaryotes

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

Lehninger 4th edition

Nuclear 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

Lehninger 4th edition

Lehninger 4th edition

The Endoplasmic Reticulum

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.

Mitochondrial Diseases

Mitochondria and Health

Animal vs. Plant Cells – Chloroplasts Are a Big Part of the Difference

The ChloroplastThink of the chloroplast as the solar panel of the plant cell.

Only plants have chloroplasts, but animals reap the benefits too.

Two Other Unique Features of Plant Cells

The central vacuole may occupy 90% of a plant cell.

Plant Organelles

• Chloroplasts–Plastids specialized for photosynthesis–Resemble photosynthetic bacteria;

may have evolved by endosymbiosis

Chloroplast

Lehninger 4th edition