Cell Theory and Cell Parts

Cell theory:

• Cells are the basic units of structures and function in all living things
• All living things are composed of cells
• New cells are produced from pre-existing cells

Cells are small. This is important because they need a high surface area-to-volume ratio.

• Volume decides the amount of chemical activity occurring in a cell
• Surface Area decides the amount of substances or particles that can pass through the cell boundary

Major Parts of the cell:

Plasma Membrane

• Made up of a phospholipid bilayer

• Plasma membranes are selectively permeable barriers
• Substances that can freely pass through:
• Small, uncharged, polar molecules
• Water through water channels called aquaporins
• Hydrophobic molecules
• O2
• Allows the cells to maintain constant internal environment
• Membrane contain proteins
• Integral membrane proteins
• Peripheral membrane proteins
• Plasma membranes are also important for receiving signals and communication

Nucleus

• Contains the DNA
• Nucleus is where DNA replication occurs
• Site of the genetic control of the cell activities
• Proteins, called histones, and DNA are combined to form chromatin
• The nucleus is surrounded by the nuclear envelope
• Nuclear pores direct the passage of molecules
• Usually the largest organelle

Ribosomes

• Ribosomes are where protein synthesis occurs
• Appear in both prokaryotes and eukaryotes
• In eukaryotes:
• They are attached to the rough ER
• Located in the cytoplasm
• Also found inside the mitochondria and chloroplasts

Endoplasmic Reticulum

• Rough ER
• Ribosomes are present
• Smooth ER
• Has no ribosomes
• Involved in the synthesis of lipids and steroids
• Involved in the breakdown of toxins, drugs or pesticides
• Involved in the hydrolysis of glycogen

Golgi Apparatus

• Golgi Apparatus modifies and packages proteins received from the ER into vesicles
• Cis region
• Receives vesicles coming from the endoplasmic reticulum
• Trans region
• Vesicles will bud off from the Golgi apparatus and onto the plasma membrane

Lysosomes

• Lysosomes are vesicles that orginate from the Golgi apparatus
• Lysosomes contain digestive enzymes

Mitochondria

• Carry out cellular respiration

Chloroplasts

• Carry out photosynthesis

Peroxisomes

• Break down substances such as hydrogen peroxide

Cytoskeleton

• Supports and maintains the cellular shape
• Positions the organelles
• Allows for some types of movement
• Three parts:
• Microfilaments
• Intermediate filaments
• Microtubules

Cilia and Flagella

• Important for motility

• Cilia
• Short and many present
• Example: can sweep away debris and other particles from the respiratory tract
• Flagella
• Long and whip-like
• Usually one or two present
• Example: can propel sperm

Cell Wall

• Provide support for the cell
• Can be found in bacteria, fungi, plants and other types of organisms 

Centrioles

• Centrioles are involved in the formation of mitotic spindle

Vacuoles

• Used as storage
• Store waste products, starch, pigments or even toxic compounds
• Can provide structural support for plant cells
• If the central vacuole was filled, then they exert pressure on the cell walls.
• This pressure is also known as turgor  

There are differences between the plant and animal cells
For example:
Typically, cell walls, chloroplasts and the central vacuoles are present in plant cells and absent in animal cells.

End of notes on cell theory and cell parts.

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