Cell Structure and Organelles

Cell Structure

• Cytoplasm is a jelly-like material that fills the cell membrane, consisting of water, proteins, nucleic acid, minerals, and ions.
• Cytosol is the dissolved material within cytoplasm.
• Cytoplasm is essential for maintaining cell structure and facilitates many biochemical reactions.

Cytoskeleton

• The cytoskeleton is a flexible network of proteins providing structural support for the cell.
• It helps maintain cell shape, internal organization, and provides mechanical support.
• The cytoskeleton consists of three main types of fibers: microfilaments, microtubules, and intermediate filaments.

Microfilaments

• Microfilaments are made of the protein actin and assist with cell movement, muscle movements, cell division, and cytoplasmic streaming.
• They keep organelles in place within the cell.

Microtubules

• Microtubules are hollow tubes constructed from the protein tubulin.
• They grow or shrink as tubulin molecules are added or removed.
• Microtubules move chromosomes during cell division and act as tracks for organelle movement.

Nucleus

• The nucleus is a membrane-bound structure that stores the cell's genetic material (DNA).
• It coordinates cell activities, including growth, metabolism, protein synthesis, and reproduction.
• The nucleus is the site of DNA replication, transcription, and ribosome synthesis.

Nucleus Functions

• The nucleus duplicates DNA during cell division, producing two identical copies.
• Transcription creates different types of RNA from DNA.
• The central rule of biology states that DNA is copied into RNA, and then proteins.

Centrioles

• Centrioles produce spindle fibers during cell division.
• They are found in motile cells of algae, fungi, and higher plants.

Nucleus Structure

• The nucleus has a double-layered membrane with large pores for material transport.
• Chromatin is the organized DNA within the nucleus, which contains proteins like histones.
• Chromatin condenses to form chromosomes, with 23 pairs in human cells.

Chromosomes and DNA

• Chromosomes are long strings or loops of DNA that carry many genes.
• In prokaryotes, DNA is organized into a single circular chromosome.
• In eukaryotes, chromosomes are linear structures, with each species having a specific number of chromosomes in their nuclei.