Cell Organelles Summary

Overview

This lecture covers major cell organelles, their structures, functions, and importance in plant and animal cells.

Cell organelles are membranous structures inside eukaryotic cells performing specialized functions.
Major organelles include nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, plastids, and vacuoles.

The ER is a large network of membrane-bound tubes and sheets similar in composition to the cell membrane.
Rough ER has ribosomes attached, which synthesize proteins.
Smooth ER lacks ribosomes and synthesizes fats (lipids).
ER provides a surface for protein and lipid synthesis and transports them within the cell.
Proteins and lipids from ER help form cell membranes (membrane biogenesis) and act as enzymes or hormones.

The Golgi apparatus is made of membrane-bound vesicles, arranged in stacks called cisterns.
It modifies, stores, and packages proteins and lipids from the ER for transport.
Called the "post office" of the cell because it directs substances to their correct destinations.
Golgi apparatus produces lysosomes.

Lysosomes are membrane-bound sacs filled with powerful digestive enzymes.
Digestive enzymes are made in smooth ER and packed in lysosomes by the Golgi apparatus.
Lysosomes break down waste, bacteria, and old organelles, keeping the cell clean.
They can self-destruct damaged cells, earning the name "suicidal sac" of the cell.

Mitochondria have a double membrane: porous outer and deeply folded inner.
They contain their own DNA and ribosomes.
Mitochondria produce energy as ATP (adenosine triphosphate), earning the name "powerhouse of the cell".

Plastids are found only in plant cells and include chloroplasts, chromoplasts, and leucoplasts.
Chloroplasts are green due to chlorophyll and conduct photosynthesis.
Chromoplasts provide colors to plant parts like flowers and fruits.
Leucoplasts are colorless and store starch, oils, and proteins.
Plastids have their own DNA and ribosomes.

Vacuoles store water, nutrients, and waste products.
Plant cells have large vacuoles filled with cell sap, giving the cell rigidity.
Animal cells have small vacuoles.
Vacuoles can occupy up to 90% of plant cell volume and push the nucleus toward the cell membrane.
In some unicellular organisms, vacuoles help expel excess water and wastes.

Cell Organelles — Specialized structures within a cell performing distinct functions.
Endoplasmic Reticulum (ER) — Network of membranes for synthesis and transport of proteins and lipids.
Ribosome — Spherical structure made of RNA and protein; site of protein synthesis.
Golgi Apparatus — Organelle that modifies, stores, and packages proteins and lipids.
Lysosome — Organelle containing digestive enzymes for breaking down waste.
Mitochondria — Organelle that generates cellular energy (ATP).
Plastid — Plant cell organelles such as chloroplasts, chromoplasts, and leucoplasts.
Vacuole — Organelle for storage of various substances within the cell.