Cell Structure and Function Notes

Cell Structure & Function

Cell Theory

• The cell theory states:
  • All biological organisms are composed of cells.
  • Cells are the unit of life.
  • All life comes from pre-existing life.
• Cells are the basic unit of a living organism, serving as building blocks.
• Microorganisms can be unicellular (single-celled) or acellular.
• Multicellular organisms are made up of many cells, with specific cells congregating to form specific body structures that serve specific functions.
• Continuity of life arises from the growth and division of single cells.
• Cells contain hereditary material which is passed on during cell division.
• Two basic cell types exist:
  • Prokaryotic cell
  • Eukaryotic cell

Cell Sizes

• Cells come in different shapes and sizes.

Cell Organelles

• Organelles are structures within a cell.

Major Structural Features of a Eukaryotic Cell

• Cell membrane (or surface membrane)
• Cytoplasm
• Nucleus
• Organelles
  • Nucleolus
  • Endoplasmic reticulum
    • Smooth ER
    • Rough ER
  • Golgi complex
  • Mitochondria
  • Lysosomes
  • Ribosomes
  • Chloroplasts (in plant cells)
  • Cell wall (in plant cells)
  • Nuclear envelope
  • Chromosomes

Structures & Functions of Cell Organelles

Nucleus

• Contains the cell’s genetic material.
• Chromatin: A threadlike mass of DNA.
• Chromatin condenses into highly coiled structures (chromosomes) during cell division.
• Nucleolus: Site for RNA synthesis and ribosome assembly.
• Surrounded by a nuclear envelope.
• Nuclear pores control the movement of substances.
• Not present in prokaryotes.

Endoplasmic Reticulum (ER)

• Netlike arrangement of flattened tubules.
• Functions as a transport system.
• Rough Endoplasmic Reticulum (RER):
  • Originates from the outer membrane of the nuclear envelope and extends in a continuous network through the cytoplasm.
  • Rough due to ribosomes on the outer surface.
  • Ribosomes produce proteins that are inserted into the lumen of the RER, where they are modified and transported to the Golgi apparatus.
• Smooth Endoplasmic Reticulum (SER):
  • Closed tubular network with no ribosomes on the surface.
  • Plays a role in lipid synthesis and transport.

Ribosomes

• Site of protein synthesis.
• Protein factory of the cell.

Smooth ER

• No ribosomes.
• Site of lipid synthesis.
• Lipid factory of the cell.

Golgi Apparatus

• Composed of a series of flattened hollow sacs.
• Shipping department of a cell; receives, processes, and packages large molecules for export.
• Transitional vesicles from the ER containing proteins go to the Golgi apparatus for modification and maturation.
• Packages molecules in vesicles, which fuse with the cytoplasmic membrane before releasing their contents outside the cell.
• The process: Nucleus $\rightarrow$ RER $\rightarrow$ Golgi apparatus $\rightarrow$ vesicles $\rightarrow$ secretion

Lysosomes

• Vesicles containing enzymes that originate from the Golgi apparatus.
• Involved in intracellular digestion of food particles and in protection against invading microbes.

Mitochondria

• Powerhouses of the cell; involved in the release of energy from food substances during respiration.
• Energy is stored in ATP (adenosine triphosphates).
• Rod-shaped structures.
• The inner membrane is folded into numerous cristae that increase the surface area.

Chloroplast

• Pigments of chloroplast (chlorophyll) convert light energy to produce sugar.
• Found in photosynthetic eukaryotes (plants).
• Numerous membranous sacs called thylakoids form an extensive surface area for chemical reactions.
• The fluid between the thylakoids and the inner membrane is called the stroma.

Summary of Major Organelles and Their Functions