Untitled Flashcards Set

MODULE 1

Lecture 1_Introduction and Cells_2025

Monday 3 March 2025    11am

Eukaryotic Cell Structure

Three Main Parts:

• Plasma Membrane

• Nucleus

• Cytoplasm

• Cytosol

• Organelles

This is a generic cell. Different types of cells have variations in structure and therefore function.

Plasma Membrane

Fluid Mosaic Model

Functions:

1. Regulates movement of substances into and out of the cell

2. Detects chemical signals coming from other cells ( intercellular communication)

3. Helps identify the cell to other cells (e.g, immunity)

4. Can link adjacent cells together for communication (e.g., between cardiac muscle cells) or for strength (e.g., epidermis of the skin)

Structure:

• Phospholipids are amphipathic and form a bilayer

• Hydrophilic (polar end containing phosphate group)

• Hydrophobic (non polar end containing fatty acids)

• Cholesterol stabilize the membrane

• Glycocalyx is the arrangement of outer glycolipids and glycoproteins for cell recognition

• Proteins have many functions

Plasma Membrane- Protein Functions

1. Ion Channel (Integral) – Forms a pore for specific ions to cross the membrane.

2. Carrier (Integral) – Transports substances by changing shape.

3. Receptor (Integral) – Binds to specific ligands to alter cell function.

4. Enzyme (Integral and Peripheral) – Catalyzes reactions inside or outside the cell.

5. Linker (Integral and Peripheral) – Anchors filaments and provides structural stability.

6. Cell Identity Marker (Glycoprotein) – Distinguishes cells from others (e.g., MHC proteins).

These proteins play key roles in transport, signaling, structure, and immune recognition.

Nucleus

Functions

1. Stores genetic information (DNA) needed to direct cell activities (e.g, protein synthesis)

2. Ensures transmission of genetic information to the next generation of cells (cell division - mitosis/meiosis)

3. Contains the nucleolus which assembles ribosomes

4. Is surrounded by its own membrane which contains nuclear pores

Most cells have one nucleus (uninucleate), some cells are multinucleate (e.g., skeletal muscle cells), and others are anucleate losing their nucleus when they mature (e.g., RBCs)

Flow of Genetic Information - Gene Expression

A gene is a segment of DNA containing the code for how to make one protein. It occurs in 2 steps.

Transcription

• The DNA sequence/template from one gene is copied as messenger RNA which exits the nucleus

Translation

• Ribosomes use the messenger RNA sequence to assemble amino acids in the correct order to make the protein.

Ribosomes

• Protein Factories

• Amino acids are assembled in different combinations and permutations to form the diverse range of proteins in the human body.

• Can be found floating free in the cytosol or attached to the rough endoplasmic reticulum

Think about how resistance training can lead to increased muscle size.

Endoplasmic reticulum (ER)

Rough ER

• Extends from the nuclear membrane

• Covered in ribosomes

• Manufactures, folds and processes proteins to be distributed to other organelles, the plasma membrane or secreted out of the cell.

Smooth ER

• No ribosomes

• Contains enzymes for fatty acid and steroid synthesis

• In the liver, enzymes help release glucose into blood while other enzymes detoxity harmful substances

• In muscle cells, lumen is a store for calcium ions

Golgi Complex

• Consists of curved, flattened membranous sacs

• Modifies, sorts, packages and transports proteins received from rough ER

• Forms secretory vesicles which ferry the processed proteins to other organelles, plasma membrane or out of the cell by exocytosis.

Lysosomes

• Organelle containing powerful digestive enzymes with an acidic (low pH) environment

• Abundant in macrophages (type of immune cell) to breakdown bacteria

• Breaks down worn out organelles and other cellular debris

• Can also destroy the entire cell (autolysis)

Cytoskeleton

• Refers to a variety of protein filaments that provide scaffolding and movement of organelles and whole cells

•  Microfilaments are involved in muscle contraction (e.g., actin) and changes in cell shape during movement and cell division

• Intermediate filaments help resist mechanical stress and can attach cells to one another.

• Microtubules are hollow tubes of proteins that help determine cell shape, movement of organelles such as vesicles and cell extensions (e.g., cilia, flagella)

Mitochondria

Structure:

• Elongated and spherical structure

• Outer membrane separates the mitochondria from the surrounding cytosol

• Inner membrane folded into cristae allow for large surface area for enzymes and chemical reactions

Function:

• Known as the powerhouse of the cell

• Transfers chemical energy from nutrients to generate ATP molecules (aerobic cellular respiration). C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP energy

Think about the adaptations to endurance exercise training leading to increases numbers and size of mitochondria.