Lecture #2 - Cell Biology #1

Cells =

 building blocks → tissues → organs → systems

What is is required to understand disease?

Understanding cell biology

Cells act like what?

 multicellular “social organism” → cellular crosstalk/communication is central.

a. Prokaryotes

b. examples

a. No distinct nucleus (lack of nucleus)

b. Examples: E. coli, Streptococcus

a. Eukaryotes

b. found in…

a.

• Well-defined nucleus

• Complex and highly organized

• Membrane-bound organelles

b. Found in: animals, plants, fungi, protozoa

What cells must do (core functions)

• Movement

• Conductivity (electrical activity)

• Metabolic absorption (bring in fuel)

• Secretion

• Excretion

• Respiration

• Reproduction

• Communication

Cellular components covered

1. Plasma membrane (cell membrane / lipid bilayer)

2. Cytoplasm (cytosol + matrix + organelles)

3. Nucleus

4. Ribosomes

5. Endoplasmic Reticulum (ER)

6. Golgi complex

7. Lysosomes

8. Peroxisomes

9. Mitochondria

10. Cytoskeleton

Plasma membrane

a. Structure

b. key concept

a. Think: fluid mosaic model → membrane proteins are not fixed; they’re constantly changing (added/removed/replaced) based on cell needs.

b. Outer casing of the cell

• Selective permeability

The plasma membrane is composed primarily of…

amphipathic molecules.

Plasma membrane

What passes through easily?

• Lipid-soluble molecules pass unaided

  • Example: steroid hormones (derived from cholesterol)

  • Therefore their receptors are inside the cell (in cytoplasm), not on the surface.

• Not lipid-soluble → needs transport (channel, pump, carrier, or vesicle uptake)

Plasma membrane

What is Caveolae?

• Membrane invaginations that pinch off into the cytoplasm

• Bring substances into the cell as vesicles

Cytoplasm

What it is?

• Space between plasma membrane and nuclear envelope

• Not “just jelly” — it’s a major functional compartment

Cytoplasm

a. What happens

b. what’s stored here

a. Glycolysis occurs here

• Key regulatory enzyme mentioned: PFK-1 (phosphofructokinase) (exists in cytoplasm)

b. Storage:

• ATP

• Ions (Ca²⁺, Na⁺, Mg²⁺, etc.)

• Phosphocreatine (PCr)

• Creatine kinase

• Glycogen

• Myoglobin (oxygen carrier inside cells)

Cytoplasm

Myoglobin:

a. what it does?

b. affinity level?

c. how many are there?

d. example…

a. Carries oxygen inside the cell (hemoglobin carries O₂ in blood)

b. Higher O₂ affinity than hemoglobin → helps oxygen move from blood → muscle cell

c. Dynamic expression: endurance-type activity / high O₂ demand → ↑ myoglobin

d. Food analogy:

• Red meat darker = more myoglobin (more iron-rich)

• Chicken lighter = less myoglobin

Cytoplasm

ATP depletion concept

• ATP depletion is NOT uniform across the whole cell

• Localized depletion happens in the most active regions

• “That’s a great test question.” ✅ ON EXAM ⭐ EXAM FLAG

Cytoplasm

a. define cytosol…

b. how much is there?

a. Cytosol = gelatinous/semi-liquid part of cytoplasm

b. About 55% of cell volume

• Dynamic volume: cells can grow/shrink (cytoplasmic hypertrophy = ↑ cytosol volume)
  

Nucleus

Structure (parts to know)

• Nuclear envelope

• Nuclear pores

• Nucleolus

• DNA

• RNA

• Histone proteins

Nucleus

Function highlights

• Control of genetic information

• Cell division

• Cell already contains the information; external cues drive specialization

  • example

    • Stem cell (blank)→ satellite cell → muscle cell

Ribosomes

a. made of what?

b. function…

c. what important here…

a. Made of RNA + proteins

b. Where protein synthesis begins

c. Free vs attached ribosomes is important

Ribosomes

Free ribosomes

• float in cytoplasm

• Make proteins used inside the cell (cytosol, nucleus, etc.)

Ribosomes

Attached ribosomes

• on rough ER

• Make proteins for:

  • Secretion

  • Membranes

  • Packaging into organelles

ER (overview)

a. structure

b. function

c. smooth and rough ER

a. Network of channels/sacs (smooth vs rough)

b, the cell’s factory + storage room.

c. Rough ER = “protein factory line” (has ribosomes → makes proteins)

• Smooth ER = “calcium storage tank” (stores Ca²⁺, especially in muscle/heart)

 many membrane proteins are…

preassembled + stored near membrane → fast deployment

Rapid “prebuilt” membrane protein insertion examples

• Insulin receptors / GLUT4 system idea: can be expressed quickly when glycogen is depleted

• Aquaporins: can be rapidly increased when fluid is low

 Lysosomes

a. function

a.

• Digestive / recycling system of cell

• Breaks down:

  • external material brought in

  • damaged organelles/old components (autophagy/autodigestion concept from slide)

• Products (like amino acids) get reused to build new proteins/channels/pumps

Lysosomes

Clinical tie-in the professor used…

• Cell injury → intracellular contents spill into blood:

  • creatine kinase

  • myoglobin

  • etc.

• This is why “markers” rise after major injury (e.g., intense exercise; heart injury concept referenced)

Peroxisomes

contain…

• Contain oxidative/antioxidant enzymes:

  • superoxide dismutase

  • catalase

  • glutathione peroxidase

Peroxisomes

purpose…

• neutralize reactive oxygen species (ROS)

• detoxify fatty acids/compounds

Peroxisomes

• Key physiology idea:

• ROS are normal, but excess ROS → protein/DNA damage

Peroxisomes

• Hydrogen/pH tie-in:

• ↑ H⁺ → ↓ pH (more acidic)

• kidneys help regulate H⁺ balance (prof connected this concept broadly)

CONNECTION

• Peroxisomes = cell cleanup (handle ROS and some chemical breakdown inside the cell).

• Kidneys = body cleanup (control H⁺/acid in the blood and keep pH normal).

Mitochondria

a. what are they considered…

b. function

c. structure

a. “Powerhouse” but very complex

b. Electron transport chain (ETC) occurs here

c. Has:

• double membrane

• its own mitochondrial DNA

Mitochondria

• Concept emphasized:

• Hydrogen carriers (NADH/FADH₂ idea) bring H⁺/electrons to ETC

• ETC creates H⁺ gradient → drives ATP synthase

Mitochondria

What stops cellular respiration?

• Cyanide

• cyanide inhibits Complex IV (cytochrome c oxidase); (WHAT TEACHER SAID)

• ATP synthase is Complex V (IN BOOK PER CHATGPT)

Mitochondria

What leads to cytoplasm energy movement?

 creatine/creatine kinase help move “phosphate/energy” out across mitochondrial layers

Cytoskeleton

a. known as…

b. function

c. structure

a. “Bones and muscles of the cell”

b.

• Maintains shape + organization

• Anchors:

  • channels involved in cell-to-cell communication

Mechanotransduction: mechanical strain → electrical signaling (especially emphasized for bone)

c.

• Microtubules (strength/rigidity)

• Actin (shape change, contraction, cell division)

• Contractile proteins help:

  • pull membrane during late mitosis/cell splitting

  • pull DNA strands during division (motor protein theme)

Selective permeability (nuts + bolts)

• Lipid-soluble → passes freely

• Not lipid-soluble → needs transport

  • channels/pumps/carriers

  • vesicle uptake (e.g., caveolae)

Voltage-gated ion channels (intro)

• Often have two gates:

• outer gate

• inner gate

Voltage-gated ion channels (intro)

Gates respond to…

change inside the cell (electrical change)

Voltage-gated ion channels (intro)

• Example flow:

• depolarization → gate opens → Na⁺ influx

• then membrane potential changes again → gates close

Isoform =

• subtype/variant of a receptor/enzyme/protein

• Same general job, slightly different form

Isoform examples

• Creatine kinase in mitochondria vs cytoplasm (different isoforms)

• Myosin isoforms (type differences)

• Adenosine receptors differ by tissue (heart/brain vs other tissues)

Receptors are…

highly specific (“lock and key”)

Many receptors exist on…

cell surface (he gave a rough estimate: ~10,000–20,000 on many cells)

Ligand =

hormone (he said treat as synonyms)

Receptor activation →

• signaling cascade → responses like:

  • enzyme activation

  • metabolism changes

  • protein expression changes

  • cell division, etc.

Cells must lock together to form:

• tissues → organs

Extracellular matrix (ECM) links to…

cytoskeleton (structure support)

ECM components (named)

• Collagen

• Elastin

• Fibronectin

• Proteoglycans

• Hyaluronic acid

Fibroblasts function

• Cells that lay down collagen/ECM

Fibroblasts

• Key in:

• repair

• scarring

• “skin tightening” concept (stimulate fibroblasts → ↑ collagen)

Cells “watch”…

 neighbors

If a cell becomes abnormal, what can neighbors do?

• neighbors can trigger apoptosis (programmed cell death) to prevent tumor growth

• He framed this as a normal protective “vigilant” response

Differentiation example (muscle)

• Naive muscle precursor/satellite cells proliferate

• Motor neuron contact provides a cue → differentiation into muscle cell

• Then synapse forms → muscle-nerve communication