cellular organization

lecture 3

Cell

The smallest, basic unit of life; comprises the cell membrane, cytoplasm, and nucleus.

Cell membrane

Phospholipid bilayer that encloses the cell and regulates traffic of substances.

Cytoplasm

Fluid portion of the cell containing organelles.

Cytosol

Aqueous intracellular solution that bathes organelles.

Nucleus

The control center of the cell; stores genetic material and directs cellular activities.

Nucleolus

Region within the nucleus where rRNA is synthesized.

rRNA

Ribosomal RNA; a component of ribosomes.

DNA

Genetic material stored in the nucleus; blueprint for proteins.

RNA

Ribonucleic acid used in transcription and translation.

Transcription

DNA to RNA in nucleus

Translation

Synthesis of a protein from mRNA as a template to ribosome outside of nucleus

mRNA

Messenger RNA; carries genetic code from DNA to ribosome.

tRNA

Transfer RNA; brings amino acids during translation.

Genetic code

Relation between nucleotide sequence and amino acid sequence in proteins.

Nucleotide

Building block of DNA and RNA.

DNA replication

Copying the genome; enzymes separate strands and synthesize new complementary strands.

Semiconservative replication

Each daughter DNA molecule contains one old strand and one new strand.

Endomembrane system

Group of membranous organelles that regulate protein trafficking and metabolism.

Endoplasmic reticulum

Network of membranous sacs

Rough ER

studded with ribosomes; site of protein synthesis.

Ribosome

Site of protein synthesis; can be free in cytosol or on rough ER.

Smooth ER

ER lacking ribosomes; synthesizes lipids and detoxifies substances.

Golgi apparatus

Modifies, sorts, and packages proteins from the ER; produces lysosomes and directs export.

Lysosome

Organelle with digestive enzymes; degrades waste material.

Mitochondrion

Energy‑converting organelle; produces ATP.

ATP

Adenosine triphosphate; main energy currency of the cell.

Mitochondrial membranes

Two lipid bilayer membranes enclosing the mitochondrial interior.

Chromatin

DNA wrapped around histones; condenses into chromosomes during division.

Chromosome

Condensed DNA structure visible during cell division.

Histone

Protein around which DNA winds to form chromatin.

Shape of DNA

Double Helix

Endocytosis

Active uptake of extracellular materials via vesicle formation. (active transport)

Phagocytosis

Endocytosis of large particles; relatively nonselective.

Pinocytosis

Endocytosis of small particles in fluid.

Receptor‑mediated endocytosis

Highly selective endocytosis triggered by ligand‑receptor binding.

Exocytosis

Vesicles fuse with the plasma membrane to release contents outside the cell.

Pancreatic acinar cells

Cells that produce and secrete digestive enzymes.

Secretory vesicles

Carries finished golgi products outside the plasma membrane. (Exocytosis)

Plasma membrane

Encloses the cell; protective barrier that regulates traffic.

Phospholipid bilayer

Two sheets of phospholipids forming the membrane; hydrophilic head outside, hydrophobic tails inside.

Polarity in phospholipids

Head is hydrophilic, tail is hydrophobic.

Channel proteins

Proteins that form pores to transport ions or water across the membrane, based on size & charge

Carrier proteins

Proteins that bind and shuttle specific molecules across the membrane. More selective.

Aquaporins

Channel proteins that allow water to cross membranes.

Simple diffusion

Passive transport of small molecules down a concentration gradient.

Facilitated diffusion

Diffusion requiring membrane proteins for larger/charged/polar molecules.

Passive transport

Movement across the membrane without cellular energy.

Active transport

Movement across the membrane using energy (ATP).

Semi‑permeable membrane

Membrane that allows some substances to cross based on size/charge.

Concentration gradient

Difference in solute concentration that drives diffusion.

Isotonic solution

Solute concentration equal inside and outside; cells remain stable.

Hypertonic solution

Higher solute concentration inside the cell than outside; water leaves the cell.

Hypotonic solution

Lower solute concentration inside the cell than outside; water enters the cell.

Concentration balance

Emerges from gradients; essential for diffusion and osmosis.

Osmosis

Diffusion of water across a semipermeable membrane

Concentration‑dependent transport

Transport that depends on gradient and membrane proteins.

Cell cycle

Sequence of events from cell creation to division.

Interphase

Cell growth and DNA replication phases: G1, S, G2.

G0 phase

Resting phase where the cell does not divide.

G1 phase

First gap phase; cell grows; prepares for DNA replication.

S phase

DNA synthesis and replication.

G2 phase

Second gap phase; cell prepares for division.

M phase

Mitotic phase; nucleus divides (mitosis) and cytoplasm divides (cytokinesis).

Mitosis

Nuclear division resulting in two nuclei.

Cytokinesis

Cytoplasm divides, yielding two separate cells.

Cyclins

Proteins that regulate progression through the cell cycle. (checkpoints)

Cyclin‑dependent kinases (CDKs)

Enzymes activated by cyclins to drive cell cycle transitions.

Spindle

Microtubule apparatus that moves chromosomes during mitosis.

Sister chromatids

Two identical copies of a chromosome held together at the centromere.

Homologous chromosomes

Pairs of chromosomes with same gene loci, one from each parent.

Nuclear DNA packaging

DNA wraps around histones to form chromatin; condenses during division.

Stem cells

Cells with the ability to differentiate into specialized cell types.

Multinucleate

Having more than one nucleus; example: skeletal muscle cells.

Skeletal muscle fiber

Long, fibrous muscle cell; multinucleated.

DNA replication enzymes

Enzymatic processes that unwind and copy DNA (general concept in notes).

Mitochondrial ATP production

Process by which mitochondria generate ATP for cellular use.

Rough endoplasmic reticulum ribosomes

They synthesize proteins destined for export or membranes.

ER lumen

internal space of the ER

Ribosome location

Ribosomes can be free in cytosol or attached to rough ER.

Proteins export via exocytosis

Exported proteins are packaged in vesicles and released by exocytosis.

Lipid bilayer organization

Hydrophobic tails face inward; hydrophilic heads face outward.

Carbohydrates in membrane

attach to lipids and proteins for recognition.

Endosome

Vesicle formed during endocytosis that sorts internalized material.

DNA helix hydrogen bonds

Two strands held together by hydrogen bonds between bases.

Chromatin condensation

Chromatin compacts into chromosomes during cell division.

Protein synthesis order

Transcription in nucleus followed by translation at ribosome.

Ribosome function

Catalyzes protein synthesis according to mRNA template.

Plasma membrane permeability

Selective permeability determines what passes through the membrane.

Anaphase (mitosis stage)

Stage where sister chromatids separate and migrate to opposite poles.

Multinucleated cells

Cells containing multiple nuclei, such as skeletal muscle fibers.

Chromosome segregation

Distribution of chromosomes into two daughter cells during mitosis.

Chromatid cohesion

Sister chromatids remain attached until anaphase.

Chromosome structure

DNA tightly packaged with histones into chromatids and chromosomes.

DNA transcription‑translation flow

DNA is transcribed to RNA and translated to protein.

Where is the site of rRNA synthesis

In the Nucleolus.

Rough vs smooth ER distinction

Rough ER has ribosomes for protein synthesis; smooth ER makes lipids.

Mitochondrion inner membrane

Inner membrane houses components of ATP production.

Cytoplasmic organization

Cytosol surrounds organelles within the cell.

Extracellular fluid vs intracellular

Fluid outside vs inside the cell; solute balance drives transport.

Spindle apparatus

Structure that ensures accurate chromosome separation.