Cell Structure and Functions

Chapter 2

Cell Organelles

Nucleus The largest organelle in animals Contains the organism’s genetic

material in the form of DNA Controls cell function by regulating

gene expression (protein synthesis) Controls DNA replication during the cell

cycle Located towards the center of the cell

for protection

Nucleus continued… Nuclear envelope (membrane) – surrounds

the nucleus to separate it from the cytoplasm Contains pores to allow RNA and proteins to

enter and leave the nucleus DNA within the nucleus is in the form of

chromatin

Nucleolus Found within the nucleus Function is to create rRNA and form

ribosomes for gene expression Ribosomes pass through the nuclear

pores into the cytoplasm

Ribosomes Consists of rRNA and proteins Used during translation of gene expression

by linking amino acids together to form proteins

Exist all through out the cell

Endoplasmic Reticulum Two types: Rough and Smooth

Rough ER Bumpy appearance due to ribosomes

that cover the outside membrane Synthesizes and packs proteins Transports the proteins that are made

from the ribosomes Forms vesicles around the proteins and

pinches off

Smooth ER Smooth appearance

because it lacks ribosomes

Acts as storage for ions and steroids for when the cell may need them.

Creates steroids and lipids

Breaks down toxic substances.

Vesicle Small, membrane-bound spheres whose

contents are isolated from the surrounding cytoplasm

Transport materials into and out of the cell using endocytosis and exocytosis

Endocytosis Endocytosis: Movement of a substance

into the cell Cell membrane forms a pouch around a

substance, then pinches off from the membrane to form a vesicle with the substance inside.

Vesicle is fused with a lysosome, which breaks down the membrane to release the food

Endocytosis continued…

Three types: Pinocytosis, phagocytosis, and receptor-mediated endocytosis

Pinocytosis: “cell drinking”. Cell is taking in a liquid substance such as extracellular fluid or dissolved particles.

Phagocytosis: “cell eating”. Cell is taking in a solid substance such as bacteria, debris, or other large objects

Pino

cyto

sis

Phagocytosis

Endocytosis: Receptor-mediated

Receptor proteins on the cell membrane recognize specific molecules that the cell needs

After ligand binds to receptor, a message is sent through the membrane to the nucleus

Endocytosis: Receptor-mediated A protein coat

forms when enough receptors are bound

Vesicle forms with the protein coat surrounding it

Vesicle will fuse with a lysosome to release the contents

Exocytosis Movement of a substance by a vesicle to

the outside of a cell. Vesicle fuses with the membrane and

releases contents, such as proteins.

Golgi Complex Vesicles with newly

made proteins are transported from the ER to the Golgi Complex.

A set of flattened, membrane-bound sacs that pack and distribute proteins

Enzymes within Golgi modify proteins and create new vesicles

Lysosomes Vesicles with newly made proteins may stay

in the cell and become lysosomes while some are released outside of the cell via exocytosis

Holds digestive enzymes Breaks down the cell when it dies, damaged

organelles, or foreign materials

Overview…1. Nucleolus creates

ribosomes2. Ribosomes move to rough

ER3. Ribosomes on rough ER

create proteins4. Rough ER transports the

proteins to the Golgi complex using vesicles

5. The vesicles fuse with the Golgi complex

6. The Golgi complex modifies the proteins using enzymes and creates another vesicle

7. The new vesicle travels to the cell membrane to be released or stays within the cell to become a lysosome

Mitochondria Harvests energy from

organic compounds to make ATP

Some cells have much more mitochondria than others, such as muscle cells.

Contains two membranes – smooth outer membrane and a folded inner membrane with large surface area.

Mitochondria continued… Also contains its own DNA and ribosomes Where cellular respiration occurs

Cellular Respiration Process of creating cell energy The cell uses oxygen to break down

glucose (sugar), which creates energy

C6H12O6 + 6O2 ⇒ 6CO2 + 6H2O + energy Sugar + Oxygen ⇒ Carbon Dioxide + water + energy

Chloroplast Only in plant cells Contains chlorophyll – gives the plant a

green color Contains a double outer membrane. Stroma - an area inside of the chloroplast

where reactions occur and sugars are created

Chloroplast Continued…

Carry out photosynthesis by capturing light and creating energy

Energy is in the form of ATP: Adenosine Tri-Phosphate

Uses the sun to convert water and CO2 into oxygen and sugar

6CO2 + 6H2O ⇒ C6H12O6 + 6O2 Carbon Dioxide + Water ⇒ Sugar +

Oxygen

Cell Wall Only found in plant cells NOT the same as the cell

membrane Composed of proteins

and carbohydrates (cellulose)

For support and shape of the cell – Rigid shape

Protects cell from damage – Strong structure

Connects with adjacent cells

Photosynthesis vs. Cellular Respiration

Vacuole Are in both plant and animals cells, but

much larger in plant cells. Stores food, waste, and water In plants, it stores a lot of water and takes

up more than ½ of the cell’s volume. Gives a plant cell support and structure

Animal vs. Plant Vacuoles