Cell Organelles Overview

Overview

This lecture covered the structure and function of the cell, describing key organelles, their components, and their roles in cellular processes.

The nucleus is the control center of the cell, surrounded by a double-layered nuclear envelope.
The outer nuclear membrane has ribosomes, allowing for mRNA binding and protein synthesis initiation.
The inner membrane contains lamins, which help structure the envelope and support cell division.
Nuclear pores in the envelope enable transport of molecules between the nucleus and cytoplasm.
The nucleolus inside the nucleus synthesizes rRNA, which combines with proteins to make ribosomes.
Chromatin consists of DNA and histone proteins, existing as euchromatin (loose, active) and heterochromatin (tight, inactive).
The nucleus is the site of DNA replication, transcription (to make mRNA, tRNA, rRNA), and ribosome production.

Rough ER has ribosomes; it synthesizes, folds, and glycosylates proteins for lysosomes, membranes, or secretion.
Smooth ER lacks ribosomes; it synthesizes lipids (fatty acids, phospholipids, cholesterol), detoxifies substances (via CYP450 enzymes), metabolizes glucose 6-phosphate, and stores calcium (especially in muscle as sarcoplasmic reticulum).

Receives vesicles from the rough and smooth ER at the cis face and ships them out from the trans face.
Modifies proteins and lipids through glycosylation (N- and O-type) and phosphorylation.
Packages modified molecules into vesicles destined for lysosomes, membranes, or secretion.

Composed of a phospholipid bilayer with hydrophilic (polar) heads and hydrophobic (non-polar) tails.
Cholesterol within the membrane regulates fluidity (more cholesterol = less fluidity).
Contains integral and peripheral proteins with functions such as transport, enzymatic activity, and cell linkage.
Acts as a selectively permeable barrier for different transport processes (simple/facilitated diffusion, vesicular transport).

Spherical organelles containing hydrolytic enzymes (proteases, nucleases, lipases, glucosidases).
Digest macromolecules, recycle worn-out organelles via autophagy, and break down damaged cells through autolysis.

Contain catalase and oxidase enzymes to break down hydrogen peroxide and participate in fatty acid oxidation.
Synthesize important lipids like plasmalogen for brain white matter and contribute to alcohol metabolism.

Powerhouse of the cell; site of ATP synthesis via oxidative phosphorylation and electron transport chain.
Has an outer membrane (high permeability), inner membrane (cristae, less permeable), and matrix.
Site of metabolic pathways: Krebs cycle, heme synthesis, urea cycle, gluconeogenesis, and ketogenesis.
Contains its own (maternal) mitochondrial DNA.

Made of rRNA and proteins; consist of a large (60S) and small (40S) subunit in eukaryotes.
Membrane-bound ribosomes synthesize proteins for export, membranes, or lysosomes.
Free ribosomes synthesize proteins for use in the cytosol.

Microfilaments (actin): support cell shape, muscle contraction (with myosin), cytokinesis, diapedesis, and phagocytosis.
Intermediate filaments: provide tensile strength, anchor cells to each other/ECM, and stabilize organelles.
Microtubules (α- and β-tubulin): enable intracellular transport (via kinesin/dynein, ATP-dependent), chromosome separation during mitosis, and form the base of cilia and flagella.

Nuclear Envelope — Double membrane surrounding the nucleus.
Lamins — Structural proteins lining the inner nuclear membrane.
Nucleolus — Site of rRNA synthesis and ribosome assembly in the nucleus.
Chromatin — Complex of DNA and histone proteins in the nucleus.
Rough ER — Membranous network with ribosomes; synthesizes and processes proteins.
Smooth ER — ER without ribosomes; synthesizes lipids, detoxifies, stores calcium.
Golgi Apparatus — Organelle that modifies, sorts, and packages proteins/lipids.
Phospholipid Bilayer — Double-layered structure forming the cell membrane.
Lysosome — Organelle with enzymes for breakdown of macromolecules and old organelles.
Peroxisome — Organelle involved in breaking down hydrogen peroxide and fatty acids.
Mitochondria — Organelle for ATP production and metabolic reactions.
Ribosome — Complex of rRNA and proteins for protein synthesis.
Cytoskeleton — Network of protein filaments for cell shape, movement, and stability.