Cell Structure and Nucleic Acids: Study Notes for General Biology

II. Nucleic Acids

Overview of Nucleic Acids

Nucleic acids are essential biomolecules that store and transmit genetic information in living organisms. They are composed of specific elements and have unique building blocks, examples, and functions.

• Elements Found in Nucleic Acids: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), and Phosphorus (P).

• Building Blocks: Nucleotides, each consisting of a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a nitrogenous base.

• Examples: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).

• Functions:

  • DNA stores genetic information and directs cellular activities.

  • RNA is involved in protein synthesis and gene regulation.

Example: DNA carries the instructions for building proteins, while RNA translates these instructions during protein synthesis.

CHAPTER 4: Cell Structure

I. Cell Theory and Cell Types

The cell theory is a fundamental concept in biology, stating that all living things are composed of cells, and that cells are the basic unit of life. Cells are classified as prokaryotic or eukaryotic based on their structure.

• Cell Theory:

  1. All living organisms are composed of one or more cells.

  2. The cell is the basic unit of structure and function in organisms.

  3. All cells arise from pre-existing cells.

• Prokaryotic Cells: Simple cells without a nucleus or membrane-bound organelles. Example: Bacteria.

• Eukaryotic Cells: Complex cells with a nucleus and membrane-bound organelles. Examples: Animal cells, Plant cells.

• Identification: Prokaryotic cells have a nucleoid region, while eukaryotic cells have a true nucleus.

Example: Bacterial cells are prokaryotic, while human and plant cells are eukaryotic.

II. Generalized Structure of Eukaryotic Cells

Eukaryotic cells share several major structural components that perform specialized functions.

• Major Parts:

  • Nucleus

  • Cytoplasm

  • Plasma (Cell) Membrane

  • Various organelles (see below)

Example: Animal and plant cells both contain a nucleus, cytoplasm, and plasma membrane, but plant cells also have a cell wall and chloroplasts.

III. Nucleus

The nucleus is a defining feature of eukaryotic cells, serving as the control center for genetic information and cellular activities.

• Structure: Surrounded by a double-layered porous membrane called the nuclear envelope.

• Contents: Contains DNA organized into chromosomes.

• Functions:

  • Site of mitosis and meiosis (cell division processes).

  • Initiates protein synthesis by transcribing DNA into RNA.

Example: The nucleus in human cells contains 46 chromosomes.

IV. Cytoplasm

The cytoplasm is the semi-fluid substance inside the cell, where most cellular processes occur and organelles are suspended.

• Properties: Slightly thicker than water due to dissolved proteins, ions, and other molecules.

• Functions:

  • Site of numerous chemical reactions essential for life.

  • Contains and supports organelles.

Example: Glycolysis, the first step of cellular respiration, occurs in the cytoplasm.

V. Organelles: Structure and Function

Organelles are specialized structures within cells that perform distinct functions. Understanding their roles is essential for studying cell biology.

Organelle	Structure	Function	Cell Type
Ribosomes	Small, non-membranous particles	Protein synthesis	All cells
Mitochondria	Double-membraned, bean-shaped	ATP production (cellular respiration)	Eukaryotic
Smooth & Rough Endoplasmic Reticulum	Network of membranes; rough has ribosomes	Protein and lipid synthesis	Eukaryotic
Golgi Body	Stack of flattened membranes	Modification, sorting, and packaging of proteins	Eukaryotic
Cytoskeleton	Network of protein filaments	Cell shape, movement, and support	All cells
Centriole	Cylindrical structures	Cell division (spindle formation)	Animal cells
Chloroplasts	Double-membraned, contains chlorophyll	Photosynthesis	Plant cells
Lysosomes	Membrane-bound vesicles	Digestion of cellular waste	Animal cells
Vesicles	Small membrane-bound sacs	Transport of materials	Eukaryotic
Nucleus	Membrane-bound, contains DNA	Genetic control center	Eukaryotic
Plasma (Cell) Membrane	Phospholipid bilayer	Regulates entry/exit of substances	All cells
Cell Wall	Rigid outer layer	Protection and support	Plant, fungi, bacteria
Central Vacuole	Large membrane-bound sac	Storage and structural support	Plant cells
Nucleoid Region	Irregularly-shaped region	Contains DNA (no membrane)	Prokaryotic

Example: Chloroplasts are found only in plant cells and are responsible for converting sunlight into chemical energy through photosynthesis.

Additional info: The table above expands on the brief list of organelles by providing structure, function, and cell type for each, ensuring a comprehensive overview for study purposes.