Study sheet: Living Biology and Cell Function

📋 Course Outline

1. Cellular Organization and Cell Types
2. Plasma Membrane Structure and Composition
3. Membrane Transport and Communication
4. Cytoplasm and Cellular Organelles
5. Cell Cycle DNA Replication and Mitosis
6. Cell Regulation Death and Meiosis
7. Genetic Material and Genome Organization
8. Gene Expression and Inheritance
9. Intercellular Messengers and Signaling
10. Receptors Potential and Cellular Responses

📖 1. Cellular Organization and Cell Types

🔑 Key Concepts & Definitions

• Cell : the fundamental structural, functional, and reproductive unit of life and the simplest organization capable of autonomous life
• Cell membrane : The cell is enclosed from the exterior by a membrane that selectively filters exchanges.

📝 Essential Points

📌 A eukaryotic cell possesses a nucleus and may be unicellular or multicellular, whereas a prokaryotic cell lacks a nucleus, as in bacteria.

💡 Memory Hook

Eukaryotes have a nucleus, whereas prokaryotes such as bacteria do not.

📖 2. Plasma Membrane Structure and Composition

🔑 Key Concepts & Definitions

• Phospholipid bilayer : a double layer of amphiphilic phospholipids with hydrophilic heads and hydrophobic lipid parts, separating two aqueous environments

★ Must-know

• The plasma membrane contains 43% lipids, 49% proteins, and 8% carbohydrates.

• Membrane proteins function as:

  • receptors
  • enzymes
  • transporters
  • ion channels
  • intracellular signal transmitters

Further detail

• Membrane carbohydrates occur in glycolipids and glycoproteins and contribute to protection, enzyme anchoring, cell adhesion, and cellular identity such as blood groups.

💡 Memory Hook

LPG: lipids, proteins, carbohydrates.

📖 3. Membrane Transport and Communication

📝 Essential Points

• Water moves across a membrane from the less concentrated hypotonic environment toward the more concentrated hypertonic environment.

📌 Passive transport requires no energy and follows the concentration gradient, whereas active transport requires energy and moves substances against the concentration gradient.

• The Na+/K+ pump is an active transporter that brings K+ into the cell and expels Na+, contributing to the membrane potential.

📌 Exocytosis exports macromolecules by vesicle fusion with the plasma membrane, whereas endocytosis imports material into the cell, including microorganisms or dead cells by phagocytosis.

💡 Memory Hook

Passive transport follows the concentration gradient, whereas active transport uses energy against it.

📖 4. Cytoplasm and Cellular Organelles

🔑 Key Concepts & Definitions

• Cytoplasm : the cell contents composed of 80% water, including the cytosol and organelles

★ Must-know

• The rough endoplasmic reticulum contains ribosomes and assembles and transports proteins toward the Golgi apparatus, whereas the smooth endoplasmic reticulum synthesizes lipids and participates in glycosylation and calcium storage.

• Mitochondria contain their own mitochondrial DNA and produce ATP through the degradation of carbohydrates, lipids, and amino acids, including the Krebs cycle.

• The Golgi apparatus matures and packages proteins, lysosomes digest ingested material and worn organelles, ribosomes synthesize proteins, and centrioles form the centrosome involved in cell division.

• The nucleus stores hereditary information, supports DNA replication and cell multiplication, and contains the nuclear envelope, nucleolus, and uncondensed chromatin.

Further detail

• The cytosol contains 85% water, ions such as K+, gases such as O2 and CO2, and dissolved mineral salts.

💡 Memory Hook

A cellular factory: the ER builds, the Golgi packages, mitochondria provide energy, and lysosomes recycle.

📖 5. Cell Cycle DNA Replication and Mitosis

📝 Essential Points

• 🔄 The four phases of the cell cycle are:

  1. G1: growth and preparation
  2. S: DNA replication
  3. G2: preparation for mitosis
  4. M: mitosis

• During S phase, DNA replication produces two copies of the genome in the nucleus.

• DNA replication is semiconservative, bidirectional, and asymmetric: each parental strand is copied by DNA polymerase to form a daughter DNA molecule containing one parental and one newly synthesized strand.

• 🔄 The mitotic sequence is:

  1. prophase
  2. prometaphase
  3. metaphase
  4. anaphase
  5. telophase
  6. cytokinesis

💡 Memory Hook

Pour Mon Amour Toujours: Prophase, Metaphase, Anaphase, Telophase.

📖 6. Cell Regulation Death and Meiosis

🔑 Key Concepts & Definitions

• Meiosis : the division reserved for reproductive cells during gametogenesis and consists of two successive divisions after one S phase

★ Must-know

📌 Cell-cycle checkpoints monitor DNA quality and quantity and preserve the ordered sequence of the four phases to prevent uncontrolled proliferation associated with cancers.

📌 Apoptosis is programmed natural cell death involving mitochondria, whereas necrosis is uncontrolled accidental death caused by conditions such as nutrient or oxygen deficiency and produces inflammation.

• Meiosis reduces the chromosome number from 46 diploid chromosomes to 23 haploid chromosomes in gametes and generates genetic mixing through random gene distribution.

Further detail

• Cell-cycle regulation involves cyclin-dependent kinases and the Rb protein, while mutations may cause overexpression of stimulatory proteins or loss of inhibitory proteins.

💡 Memory Hook

Apoptosis is programmed and natural, whereas necrosis is accidental and inflammatory.

📖 7. Genetic Material and Genome Organization

🔑 Key Concepts & Definitions

• DNA and RNA : DNA is deoxyribonucleic acid and RNA is ribonucleic acid; DNA consists of two complementary nucleotide strands in a double helix.

📝 Essential Points

• Complementary bases pair as A-T in DNA, A-U when RNA is involved, and G-C, with purines pairing with pyrimidines.

📌 A gene is a DNA fragment containing information for producing a protein, a chromosome is one compacted DNA molecule containing many genes, and the genome is all the DNA of a cell.

• The human chromosome complement contains 22 pairs of autosomes and one pair of sex chromosomes, giving 46 chromosomes: XY in males and XX in females.

💡 Memory Hook

Gene → chromosome → genome: information units become compacted DNA structures within the whole cellular DNA.

📖 8. Gene Expression and Inheritance

🔑 Key Concepts & Definitions

• Allele : an alternative form of a gene that produces a variation in gene expression

★ Must-know

• Transcription occurs in the nucleus when RNA polymerase copies a gene into pre-messenger RNA, which is matured into messenger RNA and exported to the cytoplasm.

• Translation occurs in the cytoplasm when ribosomes read messenger RNA codons and assemble a polypeptide chain from amino acids until a stop codon is reached.

📌 A homozygous individual has two identical alleles for a gene, whereas a heterozygous individual has two different alleles.

Further detail

• A dominant allele is expressed over a recessive allele, so in the stated eye-color example a dominant brown allele produces a brown phenotype over a recessive blue allele.

💡 Memory Hook

DNA → mRNA → protein: transcription precedes translation.

📖 9. Intercellular Messengers and Signaling

★ Must-know

• Intercellular communication uses signals whose production begins and whose degradation ends the message, and it is essential for organismal survival.

• Communication types by distance are:

  • intracrine and autocrine
  • paracrine
  • endocrine
  • synaptic

• Major chemical classes of diffusible messengers include:

  • cholesterol-derived steroids
  • tyrosine-derived hormones
  • peptide hormones
  • protein hormones

📌 Hydrosoluble messengers are stored in lipid-walled vesicles, whereas liposoluble messengers are synthesized when needed and are not stored in vesicles.

Further detail

• Cell communication may occur by surface proteins in direct contact, by electrical cytoplasmic gap junctions, or through information supplied by the environment.

💡 Memory Hook

Hydrosoluble hormones act through membrane receptors, whereas liposoluble hormones cross the membrane and bind intracellular receptors.

📖 10. Receptors Potential and Cellular Responses

🔑 Key Concepts & Definitions

• Receptor : a protein that binds a ligand and transduces the signal by relaying, amplifying, and integrating information for the cell
• Ligand : a molecule that binds reversibly to a receptor, whose action occurs after ligand binding

★ Must-know

📌 Hydrosoluble protein hormones bind membrane receptors and can trigger secretion or transcription, whereas liposoluble hormones cross the phospholipid bilayer and bind cytosolic or other intracellular receptors to regulate transcription.

📌 Lipophilic molecules can cross the plasma membrane spontaneously down their concentration gradient, whereas hydrophilic molecules require channels or transporters.

• The Na+/K+ ATPase maintains high extracellular Na+ and high intracellular K+, creating concentration and electrical differences across the plasma membrane.

• Changes in membrane charge generate action potentials that propagate neuronal signals, trigger calcium-dependent exocytosis in secretory cells, and coordinate atrial and ventricular cardiac contraction.

Further detail

• Messenger modification may involve:
  • hydroxylation
  • deiodination
  • proteolysis
  • oxidation-reduction

💡 Memory Hook

Ion concentration differences → membrane potential changes → cellular actions such as secretion, contraction, or signal propagation.

📊 Synthesis Tables

Membrane Transport Comparison

Transport	Energy	Direction or mechanism
Passive transport	No energy	Down the concentration gradient
Active transport	Energy required	Against the concentration gradient
Exocytosis	Vesicle fusion	Macromolecules leave the cell
Endocytosis	Vesicle formation	Material enters the cell