CELL ORGANELLES & ITS STRUCTURES

Eukaryotic Cells

these cells are multicellular and reproduces through sexual reproduction

Cell Membrane

-”edge of life”

-responsible for separating external environment and internal environment

-selectively permeable

• Proteins

• Oxygen

• Glucose

• Water

• Ions

• Carbon Dioxide

Supplies being entered and being exited from the cell membrane

Phosphate Group

It is the hydrophilic head part of the amphiphatic molecule

Amphiphatic Molecule

is a chemical compound containing both polar (water-loving/hydrophilic) and nonpolar (water-fearing/hydrophobic) parts.

Triglyceride

It is the hydrophobic tail in the amphiphatic molecule

Integral Proteins

these proteins are embedded in the phospholipid bilayer

Aquaporis

It is the channel of the integral proteins and allows water molecules to pass

Carrier

this part of the integral protein changes the shape and size and is also responsible for glucose transport

Peripheral Proteins

proteins NOT embedded in the cell membrane, only at the surface

They often act as custom messengers. When an integral protein receives a signal from outside the cell, it passes the message to a peripheral protein on the inside, which runs off to tell the rest of the cell what to do.

Cell-to-cell Recognition

this process recognizes foreign materials (immune system)

Glycoprotein

carbohydrate covalently bonded with protein

Glycolipids

carbohydrates covalently bonded with lipids

Fluid Mosaic Model

this describes the cell membrane as a dynamic, flexible structure composed of diverse molecules. First proposed in 1972, it gets its name because the lipid bilayer acts like a two-dimensional liquid ("fluid") and is studded with a diverse array of drifting proteins, cholesterol, and carbohydrates ("mosaic").

S.J. Singer & G.L. Nicholson

They proposed the Fluid Mosaic Model

Sandwich Method

is a historical biological theory proposed in 1935. It describes the membrane as a "lipo-protein sandwich," where a central phospholipid bilayer is perfectly enclosed by two continuous layers of globular proteins

Hugh Davson & James Danielli

They proposed the Sandwich Method

Cell Wall

functions as a support and protection from bursting (lysis) and also helps rigidity

Middle Lamella

the outermost layer of a cell wall; glue to adjacent cells

Pectin

the glue of the middle lamella

Primary Cell Wall

thin, flexible layer laid down ; young ; responsible for cell growth

Secondary Cell Wall

thick, rigid layer formed after the cell stops growing ; it thickens until it forms wood

Meristematic Tissue

They are made up of young, unspecialized cells that do one primary job: divide constantly to produce new cells, allowing the plant to grow

Apical Meristem

Found at the very tips of the roots and the shoots (buds).

• What it does: It drives primary growth, making the plant grow taller into the air and push deeper into the soil to find water.Apti

Lateral Meristem

Found running along the sides of stems and roots in woody plants.

• What it does: It drives secondary growth, making the plant grow wider and thicker. This is what creates tree rings and bark (cambium).

Intercalary

Found at the bases of leaves or nodes (the joints on a stem), mostly in grasses.

• What it does: It allows rapid lengthening. This is the reason grass keeps growing upward even after you cut it with a lawnmower!

Nucleus

controls the cell’s activity

Nuclear Envelope

is a double-layered membrane that encloses the cell's nucleus, separating the genetic material from the surrounding cytoplasm. It consists of an inner and outer lipid bilayer that guards the DNA while connecting directly to the cell's internal transport network, the endoplasmic reticulum

Nuclear Pores

are large, protein-lined channels embedded throughout the nuclear envelope that act as selective gateways. They regulate the vital traffic entering and exiting the nucleus, allowing small molecules to pass freely while strictly vetting large molecules like RNA and proteins.

Nucleolus

is a dense, distinct region nestled inside the nucleus that acts as a factory for building ribosomes. It does not have its own membrane, but instead aggregates RNA and proteins together to assemble the machinery the cell needs to synthesize proteins.

Nucleoplasm

is the thick, gelatinous fluid that fills the inside of the nucleus, serving as the suspension medium for the cell's genetic material. This nutrient-rich liquid provides structural support to maintain the shape of the nucleus and contains the enzymes and raw materials necessary for DNA replication and gene expression.

Ribosome

organelle that is responsible for protein synthesis

Rough ER

gets its name from its bumpy, "rough" appearance under an electron microscope.

• Structure: It is covered in millions of tiny, membrane-bound ribosomes.

• Protein Synthesis

• Protein Folding and Quality Control

• Glycolisation

Smooth ER

• Lipid and Steroid Synthesis

• Detoxification

• Calcium Storage

• Carbohydrate Metabolism

Plasma B Cells

location of RER

Pancreatic, Muscle, Bone, Liver Cells

location of Smooth ER

Golgi Apparatus

• biosynthetic factory

• receiving, sorting, modifying, and packing proteins.

• creates “transport vehicles”.

Glands

location of golgi apparatus

Mitochondria

• are responsible for generating the chemical energy required to power the cell's biochemical reactions.

• ATP Production

• Apoptosis

• Calcium Homeostasis

Outer Membrane

Mitochondria - Smooth and protective, acts as a barrier to the cytoplasm.

Inner Membrane

Mitochondria - Highly folded into pleats called cristae. These folds maximize the surface area available to pack in protein complexes for energy production.

Intermembrane Space

Mitochondria - The narrow region between the inner and outer membranes, crucial for building up a proton gradient.

Matrix

Mitochondria - The fluid-filled central space inside the inner membrane. It contains the mitochondrion's own independent DNA (mtDNA), ribosomes, and metabolic enzymes.

Cytoskeleton

• holding the organelles in place

• “foundation of the structure of the cell”

Camillo Golgi

Founder of the Golgi body

Microtubules

are stiff, hollow tubes that act as the primary structural girders and internal highway tracks of the cell.

• Size: The largest of the three, with a diameter of about 25 nm.

• Structure: Built from dimers of two globular proteins: $\alpha$-tubulin and $\beta$-tubulin. These dimers string together into linear strands called protofilaments, and 13 of these protofilaments wrap around to form a hollow cylinder.

• Dynamic Instability: They are highly dynamic, rapidly growing or shrinking by adding or losing tubulin dimers at their ends.

• Key Functions:

  • Intracellular Transport: They serve as tracks for motor proteins (kinesin and dynein) to walk along, transporting vesicles and organelles.

  • Cell Division: They form the mitotic spindle, which physically grips and pulls chromosomes apart during mitosis.

  • Motility: They make up the internal core structure of cilia and flagella, allowing cells to swim or sweep away debris.

Microfilaments

are highly flexible, solid rods that excel at bearing tension and driving cellular movements.

• Size: The smallest of the three, with a diameter of about 7 nm.

• Structure: Composed of a globular protein called actin ($G\text{-actin}$). These actin molecules polymerize into long chains ($F\text{-actin}$), and two chains twist around each other like an intertwined pearl necklace.

• Dynamic Nature: Like microtubules, microfilaments are highly dynamic and can rapidly assemble and disassemble to change cell shape.

• Key Functions:

  • Muscle Contraction: Interacting with the motor protein myosin, they generate the mechanical force required for muscles to contract.

  • Cell Shape and Support: They form a dense network just beneath the plasma membrane (the cortex) to give the cell mechanical strength.

  • Cell Movement: They drive amoeboid movement and the extension of pseudopodia (cell "crawling").

  • Cytokinesis: During cell division, a ring of actin and myosin pinches the cytoplasm in half to separate the two new daughter cells.

Intermediate Filaments

are tough, rope-like fibers designed exclusively for structural stability and mechanical strength.

• Size: As the name implies, they have a middle-tier diameter of about 8–12 nm.

• Structure: Unlike the other two, they are not made of globular proteins. Instead, they are woven from elongated, fibrous protein subunits (such as keratin in skin cells, lamins in the nucleus, or vimentin). These fibrous strands twist together into a dense, multi-stranded cable.

• Static Nature: They are highly stable and permanent. They do not display the rapid assembly/disassembly seen in microtubules or microfilaments.

• Key Functions:

  • Tension Bearing: They act like the steel cables of a suspension bridge, preventing cells from tearing when subjected to physical stretching or mechanical stress.

  • Organelle Anchorage: They lock the nucleus and other vital organelles firmly into place within the cytoplasm.

  • Nuclear Integrity: A specialized type called nuclear lamins lines the inside of the nuclear envelope, giving the nucleus its structural shape and protecting the DNA.

Lysosomes

• “suicide bay”

• has hydrolitic enzymes (contains acid)

• autophagy

• phagocytosis

• apoptosis

P53

repairs damaged DNA, if failed it will do apoptosis

Epithelial Cells

cells found on the skin

Centrosome

• cell division

• major component of microtubules

Cilia

• looks like a “whip”

• used for movement for cleaning foreign bodies

• in respiratory tract

Flagella

• cell responsible for mobility and propellity

• in sperm cells (monotrichous)

Vacuoles

• a storage for nutrients in animal cells

• a storage for water for plant cells