Biology ch. 7.3

Eukaryotic Cell Structure

Cellular Boundaries

• Cell Wall- is a fairly rigid structure located outside the plasma membrane that provides additional support and protection.
• Cell walls are composed of a carbohydrate called cellulose.
• Plant cells, fungi, bacteria and some protists have a cell wall.

The Nucleus and Cell Control

• Nucleus- controls the making of proteins, which are crucial to every part of the cell, and, therefore, controls the activities of the organelles.
• Chromatin- are strands of the genetic material, DNA. Chromatin contain the directions for making proteins.

• When a cell divides, the chromatin condenses to for chromosomes.
• Nucleolus- a prominent organelle within the nucleus which makes ribosomes.
• Ribosomes- are the sites where the cell produces proteins according to the directions of DNA. Ribosomes are not bound by a membrane, and are made of RNA and protein.

• For proteins to be made, ribosomes must leave the nucleus through the nuclear envelope and enter the cytoplasm, and the blueprints contained in DNA must be transplanted into RNA and sent to the cytoplasm.
• Cytoplasm- is the clear, gelatinous fluid inside a cell that suspends a cells organelles.
• Ribosomes and translated RNA (tRNA) are transported through the nuclear envelope.

• Nuclear envelope- is a double membrane made up of two phospholipid bilayers containing small nuclear pores for substances to pass through.

Organelles- Assembly, Transport and Storage

• Endoplasmic Reticulum (ER)- is the site of cellular chemical reactions. The ER is arranged in a series of folded membranes resembling an accordion.

• Ribosomes are attached to the surface of the ER, called the rough ER, where they carry out the synthesis of proteins.

Ribosomes

• The job of ribosomes is to synthesize proteins.
• Ribosomes attached to the ER produce a protein with a particular function:

1. It may become a protein that forms a part of the plasma membrane

2. A protein that is released from the cell

3. A protein transported to other organelles

• Ribosomes can also be found floating freely in the cytoplasm where they make proteins that perform tasks within the cytoplasm itself.

Smooth Endoplasmic Reticulum

• The smooth ER includes the areas that are not studded with ribosomes.
• Smooth ER is involved in numerous biochemical activities, including the production and storage of lipids.

Golgi Apparatus

• After proteins are made, they are transferred to the Golgi apparatus.
• Golgi apparatus- is a flattened stack of tubular membranes that sorts the proteins into packages and packs them into membrane-bound structures, called vesicles, to be sent to the appropriate destination (like mail being sorted at the post office).

Vacuoles and Storage

• Vacuoles- are membrane bound compartments used for temporary storage of food, enzymes and other materials.
• Plant cells usually have one large vacuole.
• Animal cells usually do not contain vacuoles. If they do, the vacuoles are much smaller.

Lysosomes and Recycling

• Lysosomes- are organelles that contain digestive enzymes. They digest excess or worn out organelles, food particles, and engulfed viruses or bacteria.
• Lysosomes can fuse with vacuoles and dispense their enzymes into the vacuole, digesting its contents.

Chloroplasts and Energy

• Every step we’ve discussed so far requires energy.
• Chloroplasts- are cell organelles that capture light energy and convert it to chemical energy.
• Chloroplasts are found in plants and some protists.

• Chloroplasts have an outer membrane and folded inner membrane system.
• Energy from

sunlight is

trapped in the

inner thylakoid

membrane.

Chloroplasts

• Chloroplasts belong to a group of plant organelles called plastids.
• Plastids- are organelles used for storage. Some plastids are starches or lipids, whereas others contain the pigment, molecules that give color.
• Chlorophyll- the green pigment in chloroplasts that trap light energy and gives leaves and stems their green color.

Mitochondria and Energy

• Chemical energy generated by chloroplasts is stored in the bonds of sugar molecules until they are broken down by mitochondria.
• Mitochondria- are membrane-bound organelles in plant and animal cells that transform energy for the cell.
• This energy is then stored in the bonds of other molecules that cell organelles can access easily and quickly when energy is needed.

• A mitochondrion has an outer membrane and a highly folded inner membrane.
• Energy storing molecules are produced on the inner folds

Cell Support

• Cytoskeleton- the cellular framework found within the cytoplasm composed of microtubules and microfilaments.
• Microtubules- are thin, hollow cylinders made of protein.
• Microfilaments- are smaller, solid protein fibers.
• Together, they act as a sort of scaffold to maintain the shape of the cell. Like the poles of a tent support the tent.

Centrioles

• Centrioles- are organelles found in cells of animals and most protists. They occur in pairs and are made up of microtubules. They play an important role in cell division.

Locomotion

• Some cell surfaces have organelles made of microtubules that aid the cell in locomotion or feeding.

• Cilia- are short, numerous projections that look like hairs. Their motion is similar to that of oars in a rowboat.
• Flagella- are longer projections that move with a whip-like motion. A cell usually has only one or two flagella.

Flagella

• Cilia

Comparison of Eukaryotic and Prokaryotic Cells

Cell Part

Function

Prokaryotic Cell

Eukaryotic Cell

Plasma Membrane

Maintains Homeostasis

Present

Present

Cell Wall

Supports and protects cell

Present

Present in plants

Ribosome

Makes protein

Present

Present

Chloroplast

Produces food

Absent

Present in plants

Cytoskeleton

Provides internal structure

Absent

Present

Endoplasmic reticulum

Chemical reactions

Absent

Present

Golgi apparatus

Sorts and transports

Absent

Present

Lysosome

Digests material

Absent

Present in some

Mitochondrion

Transforms energy

Absent

Present

Nucleus

Cell control center

Absent

Present

Vacuole

Storage

Absent

present

Animal Cell

Plant Cell