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Human Physiology and Anatomy Lectures by Dr. R. Ahangari, University of Central Florida

Cell Structure and Function

  • Nucleus:

    • Acts as the control center of the cell, containing genetic materials (DNA).

    • Directs the cell’s activities by providing instructions for protein synthesis.

    • Most cells possess one nucleus; however:

    • Skeletal muscle can have multiple nuclei.

    • Mature red blood cells are anucleate (lack a nucleus).

  • Main Parts of the Nucleus:

    1. Nuclear envelope

    2. Chromatin and chromosomes

    3. Nucleoli

Nuclear Envelope

  • Surrounds the nucleus.

  • Contains pores and is continuous with the endoplasmic reticulum (ER).

Nucleolus

  • A dark-staining body within the nucleus.

  • Contains parts of chromosomes and acts as the ribosome-producing machine.

  • Contains genes that code for ribosomal RNA (rRNA).

Chromatin and Chromosomes

  • Chromatin:

    • Granular, thread-like material within the nucleus.

    • Composed of DNA (Deoxyribonucleic acid) and histone proteins.

    • DNA constitutes the genetic code, which is transcribed into mRNA in a process called transcription.

  • DNA Structure:

    • DNA is a double helix made up of chains of nucleotide molecules.

    • Nucleotides consist of three components: sugar, phosphate, and one of four bases (thymine - T, adenine - A, cytosine - C, or guanine - G).

    • The bases are held together to form the DNA ladder-like structure.

    • DNA wraps around clusters of histone proteins, regulating gene expression and transcription.

    • Each cluster of DNA and histones is referred to as a nucleosome.

  • Chromosomes:

    • Each chromosome contains a single, very long segment of DNA.

    • A typical human cell contains 46 chromosomes.

    • During cell division, chromatin coils into thicker structures known as chromosomes.

The Cell Life Cycle

  • Definition: A sequence of changes a cell undergoes from formation until division.

  • Major Phases:

    1. Interphase: Cell grows and carries out its normal activities.

    2. Cell Division (Mitotic Phase): The cell divides into two cells, essential for growth and repair of tissues.

Interphase

  • A non-dividing phase where cells perform life-sustaining activities and prepare for division.

  • Consists of three subphases:

    1. G1 (Gap 1):

    • Cells grow and are metabolically active.

    • Centrioles begin to replicate.

    1. S (Synthesis Phase):

    • DNA replication occurs, resulting in identical genetic material for daughter cells.

    1. G2 (Gap 2):

    • Enzymes required for cell division are synthesized.

    • Centrioles complete replication.

    • The cell readies for mitosis.