Cell Biology

• Cell is the basic structural and functional unit of living organisms
• Its theory is a scientifically and universally accepted theory that was formulated and proposed in the mid-17th century
• Each cell performs basic life functions like reproduction, respiration, excretion, and growth
• Cells are found in all plants, animals and bacteria

History of Cell Theory

• Robert Hooke first used the term "cell" to describe box-like structures he observed in a cork slice
• Hooke's observation with a compound microscope reminded him of small rooms in a monastery
• The cell theory as known today was formulated in 1838 and 1839
• German scientist Matthias Schleiden studied plant cells, postulating every living thing is made of cells or their products
• In 1858, Rudolph Virchow completed the cell theory, stating every cell is generated from pre-existing cells
• In 1839, Matthias Schleiden and Theodor Schwann were credited with developing the cell theory

Postulates of Cell Theory

• All living things are made of one or more cells
• Living things are either unicellular (single-celled) or multicellular
• Examples of single-celled organisms include bacteria and protozoans like amoeba
• Almost all animals and plants have cells that are multi-cellular
• A human body is made of billions of cells
• "The cell is the basic structural and functional unit of life"
• All biological processes for sustaining itself rely on the presence of cells
• Cells provide structure and are crucial for vital functions, like osteocytes which make up the skeletal system in humans
• Cells are fundamental building blocks, forming cellular levels, then tissues, organs, and organ systems
• "Cells arise from pre-existing cells” Every cell is generated from another cell that existed before it
• This process of cell division allows one cell to produce more than one cell
• Cell division processes include budding or fission in yeast, and mitosis and meiosis in both plants and animals
• During cell division, a single cell divides into two or more, passing on genetic content to progeny
• Newly formed cells are usually identical to the parent cell

Modern Cell Theory

• "Energy flow occurs within cells”
• Chemical energy in cells is produced from biochemical reactions, like glucose breakdown and ATP production by mitochondria
• These reactions generate energy that flows within the cell, from one organelle to another, through chemical messengers and molecules
• "Hereditary information or DNA is passed on from one cell to another”
• Chromosomes containing genetic material pass from parent to daughter cell
• In single-celled organisms like bacteria, DNA divides into progeny through cytokinesis
• Cytokinesis results in progeny cells being genetically identical to parent cells
• In higher organisms like animals and humans, environment and recombination determine genetic makeup
• "All cells have the same basic composition”
• Cells are almost always surrounded by a cell wall and filled with cytoplasm or cytosol
• Cytoplasm or cytosol contain different structures called organelles that each have specific defined functions
• All cells have a nucleus or a region that holds the genetic content (DNA) of the organism
• All cells carryout biochemical processes and have catalysts that enable them to sustain itself

Exceptions to Cell Theory

• Viruses are non-living as they cannot replicate without a host cell
• The very first cell did not originate from a pre-existing cell
• Mitochondria and chloroplasts have their own genetic material and can reproduce independently within a cell

Organelles and Functions

• Nucleus: Stores DNA, like a room where blueprints are kept
• Mitochondria: Energy production, like a powerplant
• Smooth Endoplasmic Reticulum (SER): Lipid production and detoxification, like accessory production makes decorations etc.
• Rough Endoplasmic Reticulum (RER): Protein production, particularly for export, like a primary production line
• Golgi apparatus: Protein modification and export, like a shipping department
• Peroxisome: Lipid destruction, contains oxidative enzymes, security and waste removal
• Lysosome: Protein destruction, recycling and security

Nucleus and Cytoplasm

• Nucleus: Contains DNA blueprints packaged as a double helix
• Transformation of DNA into proteins through transcription and translation happens in the nucleus
• Cytoplasm: Jelly-like structure where cell organelles are located

Endoplasmic Reticulum

• Endoplasmic means inside (endo) the cytoplasm (plasm)
• Reticulum is derived from the latin word net
• Endoplasmic reticulum is plasma membrane inside, and it folds in to create and internal space known as the lumen

Types of Endoplasmic Reticulum

• Rough ER is studded with ribosomes for protein production
• Ribosomes travel to the rough ER and embed there when a ribosome finds a specific segment of RNA
• Smooth ER makes lipids and steroids, instead of being involved in protein synthesis
• Smooth ER is also responsible for detoxifying the cell

Golgi Apparatus

• The golgi apparatus is responsible for sending products to customers
• Responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles that translocate to cell membrane

Functions of the Golgi apparatus

• Cytosol: Proteins in the Golgi by mistake are sent back into the cytosol

• Cell membrane: Proteins for the membrane are processed continuously, then the vesicle moves to the cell membrane

• Secretion: Some proteins are meant to be secreted to act on other parts of the body. and will need a signal to be released later

• Lysosome: Final destination for Golgi proteins, containing enzymes that hydrolyze content Mitochondria

• The mitochondria are membrane-bound organelles in eukaryotic cells that generate energy

• Referred to as the powerhouse of the cell

• ATP is produced in the cell

Cytoskeleton

• It is a network of fibers within the cytoplasm responsible for cell movement and stability
• Major components of the cytoskeleton are microtubules, intermediate filaments, and microfilaments

Prokaryotes vs. Eukaryotes

• Prokaryotes: Single-celled (unicellular) without organelles or internal membranes
• Prokaryotes have a single chromosome and no nucleus, but nucleoid (a circular DNA container). They belong to domain Prokarya
• Eukaryotes: Multi-cellular organisms with a nucleus and organelles within membranes belonging to domain Eukarya

Plasma Membrane

• Prokaryote Plasma Membrane: phospholipid bilayer with proteins, often peptidoglycan cell wall (in bacteria)
• Eukaryote Plasma Membrane: phospholipid bilayer with proteins, cholesterol for fluidity. Plant/fungal cells have cellulose or chitin cell walls

Plant Cells

• Plant cells have genetic material in the nucleus and have membrane-bound organelles
• Plant cells have cell wall apart from the cell membrane
• Primarily composed of cellulose, the cell wall provides plant structure support and rigidity
• Plant cells carry out photosynthesis because of chlorophyll in their chloroplasts

Types of Plant Cells

• Parenchyma: Simplest with thin walls, used for organic products storage
• Collenchyma: Relatively thin walls with some thickening, providing structural support
• Sclerenchyma: Highly lignified cell walls, thick and in dead cells at maturity
• Water Conducting Cells: Help transmit water from roots. Has hardening agent, unlike collenchyma
• There are Xylem tracheids and vessel members cells Seedless vascular plants contain tracheids
• Angiosperm flowering plants have both tracheids and vessel members
• Sieve Tube Members: Phloem tissue conducts food produced in the leaves via photosynthesis
• Within the tissue, three types of cells found namely companion cells, phloem fibers, and parenchyma cells

Animal Cells

• Eukaryotic cells containing a "true nucleus" and membrane-bound organelles enclosed by a plasma membrane
• Unlike plants and fungi, animal cells do not have a cell wall

Types of Animal Cells

• Nerve Cells: Specialized cells that electro-chemically send impulses/info to sensory receptors and the central nervous system
• Blood Cells: Also called hematopoietic cells carry oxygen to tissues while collecting carbon dioxide
• Muscle Cells: Also called myocytes which are tubular for force and movement production.
• Skin Cells: In epidermal/dermal layers for protection, perception, and sensation transmission, as well as preventing water loss
• Bone Cells: Make up bones and the overall skeleton, providing structural support and aid in movement

Types of Cell Modification

• Apical modification
• Basal modification
• Lateral cell modification

Apical (Surface or Luminal) Modifications

• Specialized to carry out functions including secretion, absorption, and movement of luminal contents at interfaces
• Cilia: Membrane-covered extensions beat in waves, moving surface mucus. Ciliated epithelia include ciliated pseudostratified epithelium
• Flagella: For movement like cilia
• Microvilli: Brush border are plasma membrane-covered extensions with parallel actin cores
• Stereocilia: NOT TRUE CILIA and have sensory function

Basal Specialization

• Basal surface contacts the basal lamina and often contains blood borne factor receptors like hormones

Basal Lamina

• Underlies epithelial tissues and is made of collagen, proteoglycan, and laminin
• The components are contributed by epithelial/connective tissue, muscle, adipose, and Schwann cells

Lateral Modification

• Cell modification on the basal surface
• Lateral Modification Tight Junction: Acts as barriers regulating water/solute movement and prevent leakage of ECF
• Lateral Modification Adhering Junction: Anchoring junction which fastens basement membrane cells
• Lateral Modification Gap Junction: Also known as communicating junctions. Closable channels connect cytoplasm

Mitosis Interphase

• The interphase is the preparation phase for mitosis and it is also the longest phase in the cell cycle
• The interphase takes place in a cell's cytoplasm and nucleus

G1 Phase (First Gap)

• The first stage of interphase is called the G1 phase (first gap) because from a microscopic aspect, little changes are seen
• Active at the biochemical level. The Cell grows and accumulates the building blocks of chromosomal DNA

S Phase (Synthesis of DNA)

• The synthesis phase of interphase takes the longest because of the complexity of the genetic material being duplicated
• Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration.
• DNA replication results in the formation of sister chromatids that are firmly attached to the centromeric region in the S phase

G2 Phase (Second Gap)

• In the G2 phase, the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation
• Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase
• The final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis

Features of Mitosis

• In each cycle of cell division, two daughter cells are formed from the parent cell
• Known as equational cell division because the chromosome number in the parent cell and daughter cell is the same
• Mitosis leads to growth of plants
• Segregation and combination do not occur

Processes of Mitosis

• Processes occurring have been divided into different stages
• Prophase- chromatin condenses and is the beginning of prophase. Chromatin coils into chromosomes
• The mitotic spindle fibre also forms from various cytoplasmic changes
• Metaphase -The cell immediately undergoes metaphase where the cell's chromosomes align at the center of the cell equatorial plate (also called as the metaphase plate)
• Anaphase - The gradual shift from metaphase to anaphase is characterized by the breaking of the link between the sister chromatids that are about to migrate to the separate poles of the cell
• Telophase -The phase of mitosis is accompanied by cytokinesis, and the daughter cells give rise to two daughter chromosomes

Meiosis

• Meiosis is a type of cell division that involves the reduction in the number of parental chromosomes by half and the production of four haploid daughter cells
• This process is very essential in the formation of the sperm and egg cells necessary for sexual reproduction

Stages of Meiosis

• Metaphase I: Homologous chromosome pairs align randomly at the metaphase plate. Configuration becomes source of the parental genetic material
• Prophase I: Most complex stage
• Chromosomes condense and pair with homologues

Phases of Prophase 1

• Divided into five phases: leptotene, zygotene, pachytene, diplotene, and diakinesis.
• Metaphase I: Homologous chromosome pairs align randomly at the metaphase plate, therefore leading to genetic variation
• Anaphase I: Homologous chromosomes are pulled apart to opposite ends, while sister chromatids remain attached
• Telophase I: Chromosomes reach opposite poles and de-condense
• Nuclear membranes reform, and cytokinesis occurs, resulting in two haploid daughter cells
• Cells undergo meiosis I to meiosis II, without genetic material replication to ensure the daughter cells that undergo meiosis II produced during meiosis I
• Consists of : prophase II, metaphase II, anaphase II, and telophase II
• Prophase II: Similar to mitosis, with disintegration Nuclear envelope disintegrates; chromosomes condense
• Centrosomes move apart and spindle fibres attach the chromosomes Metaphase II:
• Chromosomes align at the metaphase plate
• Spindle fibres attach to centromeres, therefore ensuring separation
• Cytoplasm divides, forming haploid cells
• The cells have chromosomes due to random alignment in Meiosis 1

Importance of Mitosis

• Genetic stability ensures consistent duplication of the DNA, preventing random mutations as daughter cells are generally identical
• Growth where organisms grow because their mitotic cells greatly increase
• Replacement and Regeneration of worn-out and damaged tissue mitosis helps because worn out cells get replaced

Genetic Disorders

• Down Syndrome- A third copy of chromosome 21 Individuals “mongoloids" have attributes like the Mongolian: short neck, flat face, and below average intelligence
• Edwards Syndrome- A third copy of chromosome 18 Smaller heads, small jaw. clenched fists and overlapping fingers
• Patau Syndrome - A third copy of chromosome 13 ,the rarest yet the most severe genetic disorder Patients have polydactyly, holoprosencephaly etc Turner Syndrome- Absence of one X chromosome Females are off having short stance, and a failure to develop during period
• Metafemale- Extra X chromosome (XXX)
• Klinefelter Syndrome (XXY) Affects females who do not exhibit physical attributes, but are known to have behavior problems Affects Males specifically, it reduces overall
• Jacob's Syndrome - Extra copy of Y chromosome (XYY) Individuals are physically normal in general, however, they are taller than average

Carbohydrates

• Carbohydrates are one of the energy yielding compounds, alongside lipids, proteins and nucleic acids

Enzymes

• Enzymes, being proteins, perform specific specialized functions in biochemical compounds
• Speeds up chemical reactions to produce energy to activate the reaction

Enzymes Components

• Allosteric site is a site separate from the active site, that binds regulators, and enables the activation or deactivation of various enzymes
• Active site is the region on where the substrate binds
• Regulatory site allows binding interactions in modulating enzymes function

Redox Reactions

• Reduction Reaction: when there is a result of a molecule gaining electrons, it decreases molecules oxidation
• Oxidation Reaction: the loss of electrons increases a molecules oxidation to be more negative