Lecture 6 CSF Intro to Cells

Overview of Cell Structure & Function

• Total of approximately 37 trillion cells in the human body.

• ~13,000 reactions occur per cell per second.

Learning Objectives

1. Describe the 3 main parts of the cell: the plasma membrane, nucleus, and cytoplasm

2. Describe the structure and function of the plasma membrane, and the functions of membrane proteins

3. Describe the structure and function of the cells major organelle systems

4. Describe the structure and function of DNA, including the nucleosome, chromatin and chromosomes

5. Describe the structure and function of the cytoskeletal system

Key Cell Theory Concepts

1. All living organisms are composed of one or more cells.

2. The cell is the basic unit of structure and organization.

3. All cells arise only from pre-existing cells.

4. DNA serves as heritable material while RNA functions as a messenger.

5. Proteins are the primary workers in the cell, crucial for its functioning.

Comparison: Prokaryotes vs. Eukaryotes

• Prokaryotic cells:

  • Lack membrane-bound nucleus.

  • Smaller than eukaryotic cells.

• Eukaryotic cells:

  • Have membrane-bound organelles.

  • Generally larger in size.

• Both types contain:

  • Plasma membrane, cytosol, DNA, RNA, protein, ribosomes.

Cytoplasm and Major Organelles

• The Cytoplasm is everything inside the plasma membrane including the organelles, but not including the nucleus

• Cytosol: Fluid portion of the cytoplasm, containing water, ions, ATP, lipids, proteins.

• Major organelles include:

  • Nucleus

  • Endoplasmic Reticulum (ER) - rough and smooth

  • Golgi apparatus

  • Lysosomes

  • Mitochondria

  • Ribosomes

Endomembrane System

• Function to package, label, and ship molecules.

• Integrates with the plasma membrane.

Plasma Membrane

• Is a selectively permeable barrier

• Is made up of a double layer of phospholipids with embedded proteins

• Hydrophilic polar heads of layer will face outwards, and hydrophobic lipid tails will face inwards

Plasmamembrane Proteins

• Integral proteins: embedded in the membrane, including transmembrane proteins, mediate movement of hydrophilic substances.

  - Transmembrane Prtoeins - Are a type of Integral protein that fully span over the entire membrane

• Peripheral proteins: associated with the membrane but not embedded in it, mediate movement of hydrophilic substances

  - Often plasma membrane proteins are amphiatic (have both hydrophilic and hydrophobic regions)

• Functions Include - Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attatchment to cytoskeleton and ECM

Nucleus

• Protects DNA, Make RNA

• Protected with a double lipid bilayer called nuclear envelope which is continuous with rough ER

• Entry and exit is through nuclear pores (molecular segregation = temporal & spatial control of cell function)

• Nucleolus - rRna production occurs here, assembly of small and large subunits of ribosomes

In the Nucleus : DNA

• DNA wrapped around 8 histones = which forms a nucleosome - A collection of nucleosomes is called chromatin

• In prep for cell division, chromatin condenses to chromatin fibers then into loops and other to fully condensed chromosomes

• Chromosome contains many genes

• Gene - A DNA segment whcih contributes to phenotype/function

Ribosomes

• Function is protein production (translation), can be found either free in the cytoplasm, or attatched to the rough ER

Endoplasmic Reticulum (ER)

• Rough ER: Studded with ribosomes, produces secreted proteins, membrane proteins, organelle proteins

• Smooth ER: Lacks ribosomes; stores proteins and enzymes and produces lipids (very cell/tissue-type specific)

Golgi Apparatus Function

• Modifies, sorts, packages, and transports proteins from the Rough ER.

• Composed of flattened membrane-bound sacs (cisternae).

Lysosomes

• They’re vesicles formed from golgi membrane - Has powerful digestive enzymes

• Function is digestion substances that enter a cell, different cell components (autophagy), entire cells (autolysis) - Once digested all building blocks are recycled

Mitochondria

• Generate ATP through cellular respiration.

• Feature double membranes and contain their own genome.

Cytoskeletal System

• Maintains size, shape and integrity of the cell

• Three types of fibres:

  1. Microfilaments -

     • Actin filaments for tension and cellular motility.

     • Anchors cytoskeleton to plasma membrane proteins and are dynamic

     • Smallest

  2. Intermediate filaments -

     • Structural support, more permanent stabilizers.

     • Found in cytoplasm of cell

     • They are more permanent and less dynamic

     • Middle size

  3. Microtubules -

     • Tubulin-based structure for organelle movement and cell shape stability has lumen

     • Important for movement of cilia/flagella, and organelles

     • They are dynamic

     • Biggest