Chapter Three: Cellular Biology 1

Cells

The smallest basic structural and functional unit of all living organisms

• Diverse in size, structure, and function (many characteristics)

Ex: Humans, animals

Cell Theory

Stating all living organisms are made up of cells 

Function of a Cell

• Cell Metabolism & Energy Use: All the chemical reactions happening inside a cell that keep it alive and functioning

  • Breaking down nutrients to get energy

  • Building molecules it needs

• Synthesis Molecules: Produce proteins, nucleic acids, and lipids

• Communication: Cell communicate through electrical and chemical signals

• Reproduction: Contains DNA that determines the structural and functional characteristics of the cell  

• Maintaining homeostasis

Autophagy

To eat oneself; old cells get eaten 

• AKA Cellular Recycling 

• Also corrects mutations with certain cells 

Integral Membrane Proteins

Penetrates deeply into the lipid bilayer, in many cases extending from one surface to the other

• Hydrophobic & Hydrophilic

• Function: Transport proteins, enzymes, receptors

Ex: Sodium-Potassium Pump (Na⁺/K⁺)

Peripheral Membrane Proteins

Are attached to either the inner or outer surfaces of the lipid bilayer

• Function: Enzymes, motor proteins, cell to cell connections

Ex: G proteins

Membrane Proteins

1. Marker Molecules

2. Attachment Proteins

3. Channel Proteins

4. Carrier Proteins (Transporters)

5. ATP-Powered Pumps

6. Receptor Proteins

7. Enzymes

Marker Molecules

Are surface molecules (Peripheral Membrane Protein) that allow cells to identify other cells/molecules

• Immune ID: Identify body cells vs. foreign cells

• Cell adhesion: Help cells stick together

• Fertilization: Help sperm recognize the egg

• Tissue typing: Determine transplant compatibility

Ex: glycoproteins, glycolipids 

Glycoproteins

Proteins with attached carbohydrates

Ex: antibodies, hormones

Glycolipids 

Lipids with attached carbohydrates

Attachment Proteins

Anchor cells to other cells (cadherins) or to extracellular molecules (integrins) 

• Integral membrane proteins (deeply penetrates)

Ex: Cadherins, integrins

Cadherins

A group of proteins that attach cells to other cells

• Acts like cellular glue

Integrins

Proteins that attach cells to extracellular molecules

• A bridge that connects inside cell to outside the cell

Transport Proteins

Allow ions/molecules to move from one side of the plasma membrane to the other

• Integral membrane proteins (deeply penetrates)

Types:

1. Channel Proteins

2. Carrier Proteins

3. ATP-powered pumps

Characteristics: 

1. Specificity: each transport protein binds to and transport only a certain type of molecule/ion

2. Competition: two or more similar molecules try to bind to the same active spot on the protein

3. Saturation: The rate of movement molecules across the membrane is limited by the number of available transport proteins

Channel Proteins

Form tunnel passageways through the plasma membrane, allowing specific ions/molecules to enter or exit the cell; may be leaked or gated

• Integral membrane proteins (deeply penetrates)

• Leaked: things can pass through with ease

• Gated: things only pass through when gate opens

Leak Ion Channel

An ungated channel in cell membranes that remains constantly open to let specific ions pass through via simple diffusion

Ex: Sodium/Potassium leak channels

Gated Ion Channel

Open and close depending on certain conditions of the cell

• Some open or close in response to chemical signals binding to the channel

Ex: Ligand gated channel (chemical signal molecule), Voltage-gated channel

Ligand Gated Ion Channel

Channel only opens when a specific chemical molecule (ligand) binds to protein

Voltage-gated Ion Channel

Channel open or close in response to changes in electrical charge or voltage across the cell membrane

Carrier Proteins (Transporters)

Move ions/molecules from one side of the plasma membrane to the other

• Down gradient (High to low)

• Passive (No ATP) 

• Integral membrane proteins (deeply penetrates)

1. Specific molecule enters carrier 

2. The molecule attaches to a binding site 

3. The binding of the molecule causes changes in the shape of the protein; the carrier proteins then move the specific chemical across the plasma membrane

4. Resumes original shape and transports more   

Ex: Uniport, Symport, Antiport

Uniport (Carrier Protein)

Is the movement of one specific ion or molecule across the membrane

Symport (Carrier Protein)

Is the movement of two different ions or molecules in the SAME direction across the membrane

Antiport (Carrier Protein)

Is the movement of two different ions or molecules in the OPPOSITE direction across the membrane

ATP-Powered Pumps

Are transport proteins that require ATP to move specific ions/molecules across the plasma membrane

• Against the gradient (low to high)

• Integral membrane proteins (deeply penetrates)

1. ATP-powered pumps have binding sites, specific ions/molecules bind to

2. The breakdown (hydrolysis) of ATP to ADP releases energy, changing the shape of the protein, which moves the ion/molecule across the membrane 

3. The ion and phosphate are released from pump, and it resumes original shape

Receptor Proteins

Function as binding sites for chemical signals in the extracellular fluid; binding of chemical signals to receptors triggers cellular responses 

• Integral membrane proteins (deeply penetrates)

Ex: Acetylcholine binds to the receptor site linked to a Na+ channel, when receptor sites are not occupied by acetylcholine the channel is closed

Enzymes

Catalyze (speeds up) chemical reactions either inside or outside the cell

• Integral Membrane Protein & Peripheral Membrane Protein

Fluid Mosaic Model

• Tails (hydrophobic lipids) and Heads (hydrophilic) make up phospholipid bilayer

• Selective permeability: a process that allows certain molecules/ions to pass through the cell membrane while blocking others

Selective Permeability

A process that allows certain molecules/ions to pass through the cell membrane while blocking others

• Maintains homeostasis

• Lipids molecules (O2, CO2, and steroids) pass through the membrane

• Large, non-lipid molecules need transport proteins or vesicles to pass through membrane

Tight Junction

Cells are tightly joined together so substances can’t pass easily between them

• Function: Prevents fluid and molecules from moving between cells

Desmosome

Strong anchors neighboring cells together

• Function: Prevent cells from tearing apart

Gap Junction

Creates little channels between cells allows ions, small molecules and electrical signals to move from one cell to another

• Gap = goes between cells/communication

Solute

The substance being dissolved

Ex: salt or sugar

Solvent

The liquid doing the dissolving

Ex: warm water

Solution

A uniform, liquid mixture formed when one substance completely dissolves into another

Ex: saltwater

Transport Mechanisms

1. Passive Transport

2. Active Transport

Passive Transport

Moves substances down their concentration gradient (high concentration → low concentration) without using ATP

Ex: Diffusion, Facilitated diffusion, Osmosis

Diffusion

Substances move directly through the phospholipid bilayer (higher to lower concentration)

• Transports: Small, non-polar (uncharged) molecules

Ex: Oxygen (O₂), Carbon Dioxide (CO₂), and Lipids

Facilitated Diffusion

Substances moves high → low but needs a membrane protein to help

• Transports: Large, polar, or electrical charge molecules

Steps:

1. A glucose molecule enters a carrier protein from the extracellular fluid. The glucose binds to the carrier protein  

2. The carrier protein changes shape and releases the glucose molecule into the cell. The carrier protein then resumes its original shape to transport additional glucose molecules.

Ex: Channel & Carrier proteins

Osmosis

Water diffuses across a selectively permeable membrane

• High to low concentration

• Passive transport

Ex: Water moves from intestines into blood

Osmolarity

The measure of total solute concentration in a solution

• If solute concentration increases, water concentration decreases

• Water moves from low solute → high solute

Osmotic Pressure

The exact amount of physical pressure required to completely stop osmosis

Hypertonic Solution

Cell shrinks from losing water

• More solute (dissolved particles) outside the cell 

• Crenation: Cell shrinks 

Hypotonic Solution

Cell expands from gaining water

• Lysis: Cell bursts

Isotonic Solution

Same amount of salt inside and outside the cell; no net movement of water in or out of the cell

Active Transport

Substances moved against their concentration gradients (low to high), while using ATP

• Rate of transport depends on the concentration of substrate, the number of ATP pumps, and the amount of ATP  

Ex: Secondary Active Transport & Vesicular Transport

Secondary Active Transport

Moves molecules across cell membranes by using stored energy from an concentration gradient of another substance (Na⁺) instead of directly breaking down ATP (like active transport)

• One substance goes downhill to help another substance go uphill

Vesicular Transport

Involves membrane-bound sacs (vesicles) that move substances in and out of the cell; requires ATP 

Ex: Endocytosis, Exocytosis, Transcytosis

Endocytosis

A cell engulfs a substance from outside by folding its membrane inward to create a vesicle

• Active transport

Ex: Phagocytosis & Pinocytosis

Phagocytosis

The cell engulfs a solid particle and a large vesicle is formed

• Important to eliminating harmful substances in the body

• “Cell eating”

Pinocytosis

The cell engulfs extracellular fluid and dissolved molecules ingested and small vesicles are formed

• "Cell Drinking"

Exocytosis

A cell transports materials/waste out of the cell with internal vesicles to release their contents into the extracellular space

• Active transport

Transcytosis

Movement through a cell by a combination of endocytosis on one surface and exocytosis on the opposite surface

Cytoplasm

The cellular material outside nucleus but inside plasma membrane

• Contains: cytosol, cytoskeleton, cytoplasmic inclusions, organelles

Cytosol

The fluid portion of the cytoplasm

• Dissolved molecules, ions, and suspended molecules of proteins, give especially enzymes

Organelles

Are small, specialized structures that perform specific jobs

• Most have membranes that separate interior of organelles from cytoplasm

• There are 8 types of organelles 

Mitochondria

Produce most of the cell’s ATP through cellular respiration, which the cell uses for energy 

• Function: Perform cellular respiration, using nutrients like glucose to produce ATP

• Contains:

  • Outer Membrane: smooth, outer boundary covering the organelle

  • Intermembrane Space: narrow fluid region between outer & inner membrane

    • Key role in cellular respiration

  • Inner Membrane: Lies inside the outer membrane

    • Selective; only lets specific molecules pass through

  • Cristae: Folds of the inner membrane

  • Matrix: Gel-like fluid space enclosed in inner membrane

    • Key role in Krebs cycle; holds mitochondrial DNA

Ribosomes

Site of protein synthesis

• Made of ribosomal RNA (rRNA)

• Types: 

  • Free Ribosomes: Make proteins used inside the cell

  • Bound Ribosomes:  Ribosomes attached to ER

Rough Endoplasmic Reticulum

Ribosomes attached; protein synthesis, folding, and modifying proteins

Smooth Endoplasmic Reticulum:

No ribosomes, is responsible for producing lipids, steroids hormones, and detoxifying harmful substances

Golgi Apparatus

“Post office”; Receives proteins/lipids from ER, modifies them, sorts them, packages them, and sends them to their destinations

• Material from the ER enters the Golgi apparatus on the cis face, and exits on the trans face

Cis face

On this side of, same side of Endoplasmic Reticulum   

Trans face

Across, on the other side, Endoplasmic Reticulum

Lysosomes

Recycling/Digestive center; Membrane-bound vesicles that contain digestive enzymes

• Function: Digest bacteria/viruses/toxins, break down damaged organelles, and recycle cellular materials

Action of Lysosomes:

1. Vesicle forms and enters cytoplasm 

2. Lysosome fuses with vesicle 

3. Lysosome enzymes mix with material in vesicle and digest the material

Hydrolytic Enzymes

Use water to break larger molecules into smaller molecules (digestive enzymes)

Peroxisomes

Membrane-bound vesicles that detoxifies substances; smaller than lysosomes

• Function: Neutralize harmful substances

• Contain enzymes that break down fatty acids and amino acids

  • By-product of breakdown is Hydrogen peroxide (toxic)

  • Catalase: an enzyme that breaks down hydrogen peroxide into water and oxygen

Secretory Vesicles

Membrane-bound vesicles that stores and transports materials to the outside of the cell 

• Function: Transport materials like: hormones, enzymes, and neurotransmitters

• Pinch off from Golgi Apparatus

Proteasomes

Are large proteins complexes that contain enzymes that break down/recycle other proteins within the cell

Free Radical

An electron that doesn't bond with oxygen (dangerous)

• Occurs in Mitochondria, ER, Peroxisomes, Cell Membrane, and Cytoplasm  

Cytoskeleton

A network of protein fibers that gives the cell shape, support, organization, and movement

• 3 Main Protein Fibers: Microfilaments, Microtubules, Intermediate Filaments

Microfilaments

Made of actin; cell movement and shape changes, participate in cell division

• Smallest/thinnest type of cytoskeletal fiber

Microtubules

Made of tubulin; gives cell shape, organelles movement, chromosome movement during cell division

• Large, hollow tube shaped protein fibers 

Intermediate Filaments

Strong rope like fibers, resist pulling forces

Centrosomes

A region near the nucleus that organizes microtubules

• Function: Organizes microtubules which helps with cell division

Centrioles

Located within the centrosome

• Function: Organizes microtubules, help form mitotic spindle, help with cell division, form the bases of cilia and flagella

  • Before cell division, centrioles divide, move to the ends of the cell and organize microtubules called spindle fibers

Cilia

Short, hair like extensions on the cells surface

• Function: They move substances across the surface of the cell

Flagellum

Long, tail like extension that helps the cell move

• Ex: Sperm cell; uses its flagellum for movement

Microvilli

Tiny (microscopic) finger like projections 

• Function: Increase surface area for absorption

• Difference (Cilia & Microvilli): Cilia moves, Microvilli absorbs

Nucleus

Cells control center, contains DNA and instructions for making proteins

• Contains Nuclear envelope, Nucleolus, and Chromatin

Nuclear Envelope

A double layered membrane that surrounds and protects the nucleus, separating the DNA from the cytoplasm

• Function: Physical barrier that separates the DNA from the cytoplasm, and contains Nuclear pores that controls what enters/exits the nucleus

Nuclear Pores

Little openings inside the nuclear envelope that allows specific molecules to move between the nucleus and the cytoplasm

• Function: Selective gateways that control what enters/exits the nucleus. Allows RNA and proteins in/out of the nucleus

Nucleolus

A dense region located inside the nucleus that contains DNA

• Function: Primary site for ribosomes synthesis and RNA

Chromatin

Complex mixture of DNA, RNA, and histone proteins found in the nucleus

• DNA wraps around histones to form nucleosomes, when chromatin becomes highly condensed it forms chromosomes

• During much of cell cycle chromosomes are dispersed as chromatin

• During cell division chromatin condenses into compact chromosomes

Nucleosomes

Are structural units of chromosomes consisting of DNA wrapped around histones

• Function: Keep the DNA organized but accessible for transcription and replication

Histone

Proteins that DNA wraps around

• Function: Helps package DNA tightly so it can fit inside the nucleus

Chromosomes

Long, organized structures made of DNA wrapped around proteins called histones

• Function: Store and organize genetic information and make sure DNA can be accurately passed to new cells during cell division

DNA (deoxyribonucleic acid)

A double stranded nucleic acid molecule that contain the cell’s genetic information and instructions 

• Function: Genetic blueprint for development, functioning, and reproduction of all living organisms 

• Cannot leave the nucleus

RNA (ribonucleic acid)

A single stranded nucleic acid molecule copied directly from sections of DNA

• Function: Carries and uses genetic instructions for protein production

• Can leave the nucleus

Gene Expression

The process of using information in a gene to make a functional product, usually a protein 

• Analogy 

  • DNA = the cookbook

  • Gene = one recipe in the cookbook

  • mRNA = a copy of the recipe 

  • Ribosome = the chef 

  • Protein = the finish meal

Transcription

Making the copy of the recipe; DNA → mRNA

• The cell takes the information stored in a gene in the DNA and makes an mRNA copy of it 

Translation

Using the recipe to make the meal; mRNA → Protein

Steps:

1. The mRNA travels outside the nucleus and attaches to a ribosome

2. The ribosome reads the mRNA instructions and connects amino acids together to make a protein 

mRNA (Messager RNA)

A copy of genetic instructions from DNA

• Function: To carry the instructions from DNA to the ribosome (Process: transcription)

tRNA (Transfer RNA)

Brings amino acids to the ribosome

• Anticodon: matches a codon to mRNA; Ex: AUG - UAC

rRNA (Ribosomal RNA)

Helps makeup the ribosome and helps with protein production

Cell Cycle

Is the series of changes a cell goes through from formation until reproduction: 2 major phases: 

• Interphase: Cell grows and prepares for division

• Mitotic Phase: Cell divides

Interphase

The phase between cell divisions (occurs before both mitosis & meiosis) 

3 stages: G1 Phase, S Phase, G2 Phase

G0 Phase

A resting/inactive stage where a cell exits cell cycle 

• Stops dividing; doesn’t go through cell cycle 

G1 Phase

Growth; cell grows, makes proteins/organelles

S Phase

Synthesis; DNA replicates (copies), 1 chromosome → 2 sister chromatids

G2 Phase

Preparation; cell prepares for division

Mitosis

Division of the nucleus that produces two identical daughter nuclei 

• SISTER CHROMATIDS SEPARATE

(Diploid → Diploid, 1 cell → 2 cells)