Biotechnology 3 Unit 11 ReviewCellular Biology

Key Concepts and Terminology

• Cells are the fundamental units of life that carry out essential functions for survival and reproduction
• Prokaryotic cells lack a nucleus and other membrane-bound organelles while eukaryotic cells contain a nucleus and specialized organelles
• Cellular respiration is the process by which cells break down organic molecules to generate ATP (adenosine triphosphate) for energy
  • Aerobic respiration requires oxygen and yields more ATP compared to anaerobic respiration which occurs in the absence of oxygen
• Mitosis is the process of cell division in somatic cells resulting in two genetically identical daughter cells
  • Consists of prophase, metaphase, anaphase, and telophase stages
• Meiosis is a specialized form of cell division that produces haploid gametes (eggs and sperm) with half the genetic material of the parent cell
• Apoptosis refers to programmed cell death, a regulated process that removes damaged or unwanted cells from an organism
• Differentiation is the process by which cells become specialized to perform specific functions within a multicellular organism (neurons, muscle cells)

Cell Structure and Organization

• Cells are highly organized structures that contain specialized components called organelles, each with specific functions
• The nucleus is the control center of the cell, housing the genetic material (DNA) and directing cellular activities
  • Nuclear pores in the nuclear envelope allow for selective transport of molecules between the nucleus and cytoplasm
• Ribosomes are the sites of protein synthesis, translating mRNA into polypeptide chains
  • Can be found freely in the cytoplasm or attached to the rough endoplasmic reticulum
• The endoplasmic reticulum (ER) is a network of membranous channels involved in protein and lipid synthesis, modification, and transport
  • Smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification while rough ER is studded with ribosomes for protein synthesis
• Golgi apparatus is responsible for modifying, packaging, and sorting proteins and lipids for transport to their final destinations (secretion, plasma membrane)
• Mitochondria are the powerhouses of the cell, generating ATP through cellular respiration
  • Contain their own DNA and ribosomes, reflecting their evolutionary origin as endosymbiotic bacteria
• Lysosomes are membrane-bound organelles containing digestive enzymes that break down cellular waste, foreign particles, and damaged organelles
• Cytoskeleton is a network of protein filaments (microfilaments, intermediate filaments, microtubules) that provide structure, support, and enable cell movement

Cellular Membranes and Transport

• The plasma membrane is a selectively permeable barrier that separates the cell's interior from the external environment
  • Composed of a phospholipid bilayer with embedded proteins, cholesterol, and glycolipids
• Passive transport involves the movement of molecules across the membrane without the expenditure of cellular energy
  • Diffusion is the movement of molecules from a region of high concentration to a region of low concentration driven by the concentration gradient
  • Osmosis is the diffusion of water across a selectively permeable membrane from a region of high water potential to a region of low water potential
• Active transport requires the use of cellular energy (ATP) to move molecules against their concentration gradient
  • Sodium-potassium pump is an example of primary active transport that maintains the electrochemical gradient across the plasma membrane
• Endocytosis is the process by which cells take in materials from the external environment by invaginating the plasma membrane to form vesicles
  • Phagocytosis involves the engulfment of large particles (bacteria) while pinocytosis involves the uptake of fluids and dissolved solutes
• Exocytosis is the process by which cells release materials to the extracellular space by fusing vesicles with the plasma membrane
• Ion channels are membrane proteins that allow the selective passage of specific ions (sodium, potassium, calcium) across the membrane
  • Gated ion channels open or close in response to specific stimuli (voltage, ligands, mechanical stress)

Energy Production in Cells

• Cells require a constant supply of energy in the form of ATP to carry out various cellular processes
• Glycolysis is the first stage of cellular respiration, occurring in the cytoplasm and breaking down glucose into two pyruvate molecules
  • Yields a net gain of 2 ATP and 2 NADH (reduced nicotinamide adenine dinucleotide) molecules
• Citric acid cycle (Krebs cycle) takes place in the mitochondrial matrix, oxidizing acetyl-CoA derived from pyruvate to generate high-energy molecules (NADH, FADH2)
  • Produces 2 ATP, 6 NADH, and 2 FADH2 per glucose molecule
• Electron transport chain (ETC) is a series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen
  • Proton gradient generated by the ETC drives ATP synthesis through chemiosmosis in the process of oxidative phosphorylation
• Fermentation is an anaerobic process that regenerates NAD+ in the absence of oxygen, allowing glycolysis to continue
  • Lactic acid fermentation occurs in animal cells (muscle) while alcohol fermentation occurs in yeast and some plant cells
• Photosynthesis is the process by which plants and other autotrophs convert light energy into chemical energy stored in glucose
  • Light-dependent reactions occur in the thylakoid membranes of chloroplasts, generating ATP and NADPH
  • Light-independent reactions (Calvin cycle) take place in the stroma, using ATP and NADPH to fix carbon dioxide into organic compounds

DNA, RNA, and Protein Synthesis

• DNA (deoxyribonucleic acid) is the genetic material that stores and transmits hereditary information
  • Composed of four nucleotide bases: adenine (A), thymine (T), guanine (G), and cytosine (C)
  • Double helix structure with complementary base pairing (A-T, G-C) and antiparallel strands
• RNA (ribonucleic acid) is a single-stranded nucleic acid that plays a crucial role in gene expression and protein synthesis
  • Three main types: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
• Transcription is the process of synthesizing RNA from a DNA template, carried out by RNA polymerase
  • Occurs in the nucleus and involves the unwinding of DNA, base pairing of RNA nucleotides, and termination
• Translation is the process of synthesizing proteins from an mRNA template, carried out by ribosomes
  • Genetic code is read in triplets (codons) with each codon specifying a particular amino acid
  • tRNAs deliver amino acids to the ribosome, which forms peptide bonds between them according to the mRNA sequence
• Mutations are changes in the DNA sequence that can alter gene expression and protein function
  • Point mutations involve single nucleotide changes (substitutions, insertions, deletions) while chromosomal mutations affect larger segments of DNA (translocations, inversions)
• Regulation of gene expression allows cells to control the timing and amount of protein production in response to internal and external signals
  • Transcriptional regulation involves the binding of transcription factors to promoter regions to activate or repress gene expression
  • Post-transcriptional regulation includes mRNA processing (splicing), stability, and localization
  • Translational regulation affects the initiation, elongation, and termination of protein synthesis

Cell Division and Reproduction

• Cell cycle is the ordered series of events that lead to cell division and replication
  • Consists of interphase (G1, S, G2 phases) and mitosis (M phase)
• Interphase is the period between cell divisions where the cell grows, replicates its DNA, and prepares for division
  • G1 phase is characterized by cell growth and normal metabolic activity
  • S phase involves the replication of DNA, ensuring each daughter cell receives a complete set of genetic material
  • G2 phase is a period of further growth and preparation for mitosis
• Mitosis is the process of nuclear division in eukaryotic cells, resulting in two genetically identical daughter cells
  • Prophase: chromosomes condense, nuclear envelope breaks down, and spindle fibers form
  • Metaphase: chromosomes align at the equatorial plane of the cell
  • Anaphase: sister chromatids separate and move towards opposite poles of the cell
  • Telophase: nuclear envelopes reform around the daughter nuclei and chromosomes decondense
• Cytokinesis is the division of the cytoplasm following mitosis, resulting in two separate daughter cells
  • Occurs by cleavage furrow formation in animal cells and cell plate formation in plant cells
• Meiosis is a specialized form of cell division that produces haploid gametes (eggs and sperm) for sexual reproduction
  • Consists of two rounds of division (meiosis I and II) with one round of DNA replication
  • Meiosis I: homologous chromosomes pair, undergo crossing over, and segregate to opposite poles
  • Meiosis II: sister chromatids separate, resulting in four haploid daughter cells
• Cell cycle regulation involves checkpoints that monitor the completion of critical events and ensure the fidelity of cell division
  • Controlled by cyclin-dependent kinases (CDKs) and their regulatory partners, cyclins
  • Tumor suppressor genes (p53) and proto-oncogenes (Ras) play key roles in regulating cell cycle progression and preventing uncontrolled cell division

Cell Communication and Signaling

• Cells communicate with each other and respond to their environment through various signaling mechanisms
• Ligands are signaling molecules that bind to specific receptors on the target cell's surface or interior
  • Examples include hormones (insulin), neurotransmitters (acetylcholine), and growth factors (epidermal growth factor)
• Receptors are proteins that recognize and bind specific ligands, initiating a cellular response
  • Cell surface receptors include G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), and ion channel-linked receptors
  • Intracellular receptors are located in the cytoplasm or nucleus and bind to lipid-soluble ligands (steroid hormones)
• Signal transduction is the process by which a receptor converts the binding of a ligand into a cellular response
  • Involves the activation of second messengers (cyclic AMP, calcium) and signaling cascades (MAPK pathway)
  • Amplification of the signal allows for a small number of ligand-receptor interactions to produce a large cellular response
• Cellular responses to signaling can include changes in gene expression, protein activity, or cell behavior
  • Examples include cell proliferation, differentiation, migration, and apoptosis
• Feedback regulation allows cells to fine-tune their responses to signaling and maintain homeostasis
  • Negative feedback inhibits the signaling pathway, preventing excessive stimulation (insulin signaling)
  • Positive feedback amplifies the signaling pathway, leading to a rapid and robust response (blood clotting)
• Dysregulation of cell signaling can contribute to various diseases, including cancer, diabetes, and autoimmune disorders
  • Mutations in signaling proteins (EGFR in lung cancer) or alterations in signaling pathways (PI3K/Akt in breast cancer) can lead to uncontrolled cell growth and survival

Biotechnology Applications in Cell Biology

• Recombinant DNA technology involves the manipulation of DNA sequences to create novel genetic combinations
  • Restriction enzymes are used to cut DNA at specific sites, allowing for the insertion of foreign DNA into a vector (plasmid)
  • DNA ligase is used to join the inserted DNA to the vector, creating a recombinant DNA molecule
• Polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences
  • Involves repeated cycles of denaturation, annealing, and extension using a heat-stable DNA polymerase (Taq polymerase)
  • Allows for the rapid and specific amplification of DNA for various applications (genetic testing, forensic analysis)
• Gene therapy is the introduction of functional genes into cells to replace defective or missing genes
  • Viral vectors (retroviruses, adenoviruses) are commonly used to deliver the therapeutic gene into the target cells
  • Applications include the treatment of genetic disorders (sickle cell anemia), cancer, and infectious diseases
• Stem cell technology involves the use of undifferentiated cells that have the potential to develop into various specialized cell types
  • Embryonic stem cells are derived from the inner cell mass of blastocysts and are pluripotent (can give rise to all cell types)
  • Adult stem cells are found in various tissues (bone marrow, adipose tissue) and are multipotent (can give rise to multiple cell types within a lineage)
  • Induced pluripotent stem cells (iPSCs) are generated by reprogramming adult somatic cells to a pluripotent state using specific transcription factors
• Tissue engineering combines principles of cell biology, materials science, and engineering to create functional tissue replacements
  • Involves the use of scaffolds (natural or synthetic) to support cell growth and differentiation
  • Applications include the regeneration of skin, cartilage, bone, and blood vessels
• Biopharmaceuticals are drugs produced using living organisms or their components
  • Recombinant proteins (insulin, growth hormone) are produced by inserting the gene of interest into a host cell (bacteria, yeast, mammalian cells)
  • Monoclonal antibodies are produced by hybridoma technology, fusing antibody-producing B cells with immortal myeloma cells
  • Applications include the treatment of cancer (Herceptin), autoimmune disorders (Humira), and infectious diseases (Synagis)
• CRISPR-Cas9 is a powerful gene editing tool that allows for precise modification of DNA sequences
  • Consists of a guide RNA that directs the Cas9 endonuclease to a specific DNA sequence, where it creates a double-strand break
  • DNA repair mechanisms (non-homologous end joining, homology-directed repair) can be harnessed to introduce desired genetic changes (deletions, insertions, replacements)
  • Applications include the study of gene function, creation of disease models, and potential treatment of genetic disorders