Cells - Structure and Function of Organelles

Eukaryotic vs. Prokaryotic

• Prokaryotic organisms are single-celled bacteria that evolved early and are very simple. They do not have nuclei!

• Eukaryotic organisms evolved later and are more complex. The cells of eukaryotic organisms contain nuclei.

Prokaryotic cell = simple cell; no nucleus; evolved first

Example = Bacterial cell

Eukaryotic cell = more complex; evolved later; contains a nucleus (and many other organelles)

Example = corn cell

Plasma Membrane (“Cell Membrane”)

• Phospholipid bi-layer• Hydrophilic heads (love water)• Hydrophobic tails (hate water)• Made up of phospholipids with embedded proteins

and carbohydrates to provide functionality• Function = Protect cell from surrounding

environment and regulate what enters and leaves a cell (“traffic cop”)

• Selectively permeable• Found in ALL cells

This picture shows the plasma membranes of 2 cells lined up next to each other.

Plasma membrane - cross section

Looking down on a plasma membrane

Cell Wall

• Functions to support and protect the cell

• Only found in plant cells

• Made of the carbohydrate cellulose - a tough carbohydrate

• Very permeable (stuff still needs to get in and out of the cell!)

• Found outside the plasma membrane

Organelle

• A structure with a specialized function found within the cell

Nucleus

• Contains the genetic material of the cell (DNA)

• “Control center” (brain) of the cell

• Surrounded by a double membrane (the nuclear envelope) that has large pores

• Found in plant and animal cells but not in bacteria cells (bacteria are prokaryotes)

nucleus

Nuclear Envelope

• Double membrane that surrounds the nucleus

• Porous (has pores) and very permeable

• Allows most substances to enter or leave the nucleus

Nucleolus

• Dark staining area of the nucleus where ribosomes are made (“ribosome factory”)

• There can be more than 1 in a cell (usually 1-3)

Chromosomes

• Tightly packed chromatin (DNA and proteins) found in the nucleus

• Visible only when the cell is dividing

Human Chromosomes

Chromatin

• Thin strands of DNA and protein that condense to form chromosomes

chromatin fragments from chicken

Cytoplasm

• The watery region of a cell between the plasma membrane and the nucleus (does not include the nucleus)

• Watery solution of dissolved salts, sugars, amino acids, proteins, etc…

• In both plant and animal cells

Ribosomes

• Function in the synthesis of proteins (“protein factories”)

• Tiny and numerous organelles

• Ribosomes are usually attached to endoplasmic reticulum but can also be free within the cell

• Found in both plant and animal cells

Popeye is active because he eats spinach.However, for Popeye's cells to be active, his ribosomes help

create proteins.

Rough Endoplasmic Reticulum

• “Intracellular highway” - the path in the cell along which molecules (proteins) travel

• Called “rough” because it’s covered with ribosomes

• Found in both plant and animal cells

Smooth Endoplasmic Reticulum

• Smooth because it is not covered with ribosomes

• One main function is to breakdown toxic substances within the cell

• “HAZ-MAT team”

• In both plant and animal cells

Golgi Apparatus

• “Protein packaging factory”

• A system of membranes that prepares proteins for export out of the cell

• In both plant and animal cells

Lysosomes

• Function in digesting old materials in the cell (“recycling center”)

• Contain enzymes that do the work of breaking down large molecules

• Single membrane

• Found in animal cells, fungi, and bacteria, but rare in plant cells

Vacuoles (animal)

• Protists have contractile vacuoles that function to expel excess water out of the cell

Vacuoles (plant cell)

• Large, fluid-filled sac that stores water and dissolved solutes (such as enzymes and metabolic wastes)

• Function in structure and support of plant cells (regulates turgor pressure within the cell)

Mitochondrion (mitochondria = plural)

• Where cellular respiration occurs• ATP (cellular enery) is made out of organic

compounds• Double membrane

– Outer membrane protects mitochondrion– Inner membrane has many folds known as cristae -

these folds greatly increase the surface area of the membrane

• Contain its own DNA!• In both plant and animal cells

Chloroplast• Function in converting the energy of

sunlight into chemical energy (photosynthesis)

• “Food factory of plants”

• Contain disks (known as thylakoids) in stacks (known as grana)

• Contains a green pigment (chlorophyll)

• Only in plants

Chlorophyll

• The green pigment found in plant chloroplasts

• Used in photosynthesis to trap sunlight energy.