LSB421 week2 lecture 2

Major Organelles in the Cytoplasm

Overview

• Organelles are specialized structures within cells, performing essential functions for cell maintenance and operation.

• They are sometimes referred to as little organs.

Mitochondria

• Function: Primary generators of adenosine triphosphate (ATP), the universal energy carrier in cells.

• Known as the "powerhouses of the cell."

• Structure:

  • Smooth outer membrane.

  • Inner membrane has many folds (cristae) that increase surface area for enhanced ATP production.

• Importance in energy-demanding cells:

  • Example: Cardiac muscle cells have a high number of mitochondria due to their continuous energy needs for muscle contraction.

  • Cells with lower energy needs contain fewer mitochondria.

Golgi Apparatus

• Structure: Composed of membranous discs, situated between the endoplasmic reticulum (ER) and cell membrane.

• Functions:

  1. Modifies proteins into functional forms, occurring in the membranous disks.

  2. Packages cellular products into vesicles for transport across the cell membrane and eventual exit from the cell.

• Ensures efficient release of products and maintenance of internal cell environment.

Ribosomes

• Structure: Composed of two subunits (small and large).

• Assembly: Subunits are formed independently in the nucleolus, then migrate to the cytoplasm to unite into functional ribosomes.

• Locations:

  • Free ribosomes in the cytoplasm.

  • Bound ribosomes on the rough endoplasmic reticulum (RER).

Endoplasmic Reticulum (ER)

• Definition: A network of membranes within the cytoplasm, closely associated with the nuclear envelope.

• Types:

  Rough Endoplasmic Reticulum (RER)

  • Appears rough due to ribosomes on its surface.

  • Functions:

    • Site for protein synthesis and modification.

    • Ribosomes synthesize polypeptides, which are processed in cisternae (flattened chambers).

  • Polypeptides might:

    • Join other polypeptides to form multi-subunit proteins.

    • Undergo chemical modifications.

  Smooth Endoplasmic Reticulum (SER)

  • Lacks ribosomes.

  • Functions:

    • Produces replacement membranes for membranous cell structures.

    • In reproductive organ cells, it’s involved in steroid hormone production.

    • In adipocytes (fat cells), produces triglycerides.

Nucleus

• Function: Stores genetic material (DNA).

• Structure:

  • Enclosed in a nuclear envelope (double membrane of lipid bilayers).

  • Contains protein-lined pores for the selective exchange of molecules with the cytoplasm.

• Components:

  • Nucleolus: Specialized region for ribosomal RNA production and packaging with protein subunits.

    • Site of formation for small and large ribosomal subunits.

  • Chromatin: Combination of DNA wrapped around proteins (histones) when a cell is not dividing.

    • Allows for efficient storage and accessibility of genetic information.

  • Chromosomes: Form during cell division; tightly bundled DNA structures with proteins that maintain stability.

Review Question Reminder

• Suggested to check understanding of the basic anatomy and physiology of cells through review questions in the lecture presentation.