Cell Types, Binary Fission and Mitosis

Cell Types

• An unicellular organism is a single cell operating as a whole, like bacteria
• Multicellular organisms have specialized cells for tissues and complex organization

Binary Fission in Prokaryotes

• Prokaryotic cells reproduce quickly via binary fission, an asexual process
• Binary fission results in 2 genetically identical cells
• The circular chromosome and plasmids replicate
• The cell elongates preparing to separate, while chromosomes move to opposite ends
• Cytokinesis begins, pinching the cell inward to form a septum, dividing it into 2 new cells
• A new cell wall and membrane appear down the center of the cell
• Plasmids might not distribute evenly due to their independent replication
• Cytokinesis separates the cell into 2 new cells, dividing the cytoplasm and forming 2 daughter cells
• The stages of binary fission are DNA replication, Elongation, Septum formation, and Cell division

Mitosis vs Binary Fission

• Mitosis is how eukaryotic cells replicate, involving complete separation of sister chromatids and nuclei
• Binary fission occurs in prokaryotes like bacteria, while mitosis occurs in eukaryotes like plants and animals
• Binary fission involves a single circular chromosome; mitosis involves multiple linear chromosomes
• Binary fission is rapid and for asexual reproduction; mitosis is slower and for growth, repair, and unicellular eukaryotic reproduction

Eukaryotic Cell Cycle

• The eukaryotic cell cycle includes interphase, mitosis, and cytokinesis, ensuring growth, DNA replication and cell division

Interphase (G1, S, G2)

• The cell cycle stage involving cellular growth and chromosome duplication
• G1 Phase: Cell growth happens due to increased cytosol volume and replicating organelles, ATP production, DNA replication protein synthesis
• Post G1, the cell enters S phase or exits to G0 phase
• G0 Phase: Cells not needed for replication rest here, becoming either dormant or terminally differentiated
  • Dormant cells can re-enter the cell cycle
  • Terminally differentiated cells remain permanently specialized and no longer replicate
• S Phase: DNA replicates, turning one chromosome into 2 identical sister chromatids joined by a centromere
• G2 Phase: The cell grows and prepares for mitosis, increasing cytosol volume, creating ATP and synthesizing proteins

Mitosis (Prophase, Metaphase, Anaphase, Telophase)

• The stage involving separation of newly replicated chromosomes into 2 nuclei divided into prophase, metaphase, anaphase, and telophase
• Prophase: Chromatin condenses around histones, making chromosomes visible under a microscope, centrioles migrate, spindle fibers form, the nuclear membrane breaks down and the nucleolus disappears
• Metaphase: Spindle fibers attach to centromeres, guiding chromosomes to the cell's equator
• Anaphase: Spindle fibers contract, splitting centromeres and pulling sister chromatids to opposite ends
• Telophase: Chromosomes pack at each end of the cell, new nuclear membranes form, producing 2 identical nuclei, and spindle fibers disintegrate as the chromosomes decondense

Cytokinesis

• Final stage of cell division of cytoplasm with organelles dividing so two daughter cells form
• In animal cells, a cleavage furrow pinches the plasma membrane into 2 cells
• In plant cells, a cell plate forms at the equator before separating into 2 new cells

Cell Checkpoints

• Cell cycle regulation occurs via 3 checkpoints where the cell checks for errors before moving to the next phase
• Checkpoints occur at the end of G1, the end of G2, and during metaphase
• The cell pauses for repairs if errors are found
• Programmed cell death occurs if irreparable damage is found
• G1 Checkpoint: Verifies cell size, protein synthesis, DNA damage during mitosis/growth, and sufficient nutrients/oxygen
• G2 Checkpoint: Ensures proper DNA replication in S phase and adequate resources for mitosis
• Metaphase Checkpoint: Checks spindle fiber formation and chromosome alignment before anaphase

Stem Cells

• Stem cells undifferentiated cells capable of specializing into cells with specific functions
• Differentiation turns stem cells into specialized cells
• Potency measures to differentiate stem cells

Potency

• Totipotent: Can differentiate into any cell type, like a zygote that forms placental cells and cells for the fetus
• Pluripotent: Can differentiate into multiple cell types, like embryonic stem cells, can form all body cell types except the placenta
• Multipotent: Can differentiate into a limited range of specialized cells within a tissue or organ, eg. bone marrow producing different blood cells

Apoptosis

• Natural and controlled cell death process within the body through programmed cell death
• Apoptosis begins when cells malfunction, are damaged, or unnecessary

Necrosis

• Accidental, uncontrolled cell death, due to injury or disease

Apoptosis vs Necrosis

• Apoptosis is controlled cell death due to DNA damage or malfunction, causing no inflammation
• Necrosis is uncontrolled cell death from injury or toxins, causing inflammation

Apoptosis Initiation Pathways

• Apoptosis can be initiated by the mitochondrial pathway or the death receptor pathway, both activating caspase enzymes
  • Mitochondrial Pathway: Initiated by internal cellular damage, mitochondria detect damage releasing cytochrome c into cytosol, activating caspase enzymes leading to apoptosis
  • Death Receptor Pathway: Initiated via extracellular death signaling molecules, death receptor proteins on cell surface recognize signaling molecules and activate caspase enzymes, initiating apoptosis

Apoptosis Stages

• Involves 4 stages including digesting contents, shrinking, blebbing, and forming apoptotic bodies
• Caspases are activated after internal damage, either by mitochondrial or death receptor pathway
• Caspases cleave proteins, leading breakdown of organelles
• Cells begin to shrink
• Cytoskeleton weakens, and membranes warp, detaching as apoptotic bodies full of broken down cellular material
• Phagocytes then engulf apoptotic bodies

Plant Anatomy

• Roots are in the soil, absorbing water/nutrients and providing support
• Stems support and connect the plant, carrying water and nutrients between roots and shoots
• Stomata are pores in leaves' epidermises that regulate gas exchange, allowing CO2 in for photosynthesis and release of O2 and water vapor

Stomata Opening/Closing

• Stomata open during the day for CO2 entry for photosynthesis, releasing O2 and water vapor during transpiration in humid and still conditions
• Stomata close at night to save water, in low humidity, and windy conditions,

Guard Cells

• Control gas exchange by surrounding and regulating stomata openings, uptaking CO2 for photosynthesis and losing water during transpiration
• Water moves in as potassium ions enter guard cells, causing turgidity and opening stomata
• Water exits guard cells when potassium ions leave, causing flaccidity and closing stomata

Xylem vs Phloem

• Xylem transports water, while phloem transports sugar
• Xylem has dead, hollow tubes with vessel elements and tracheids, while phloem has living specialized cells in long, skinny tubes with sieve cells and companion cells
• Xylem moves water and nutrients upward from roots to leaves passively via transpiration
• Phloem moves sugars bidirectionally actively via translocation

Transpiration

• Water evaporates and moves up the xylem
• Water evaporates from leaf and exits through stomata
• Pressure becomes lower in the leaf than in the roots
• This low pressure draws water up the xylem by adhesion

Water Transport

• Water Entering Roots: Occurs via osmosis from high concentration in soil to low concentration in root cells; root hairs enlarge water absorption
• Water Moving Up the Plant: Cohesion/adhesion pull water through vascular tissue reaching the leaves; 3 main forces involved
  • Water molecules adhere to each other water molecules via hydrogen bonds
  • Water molecules adheres water to xylem walls
  • Transpiration pull creates negative pressure, making water moving to high to low pressure areas (roots to leaves)
• Water Moving out the leaves: Stomata release water vapor
  • Water turns into vapor
  • Water vapor goes to low humidity
  • High transpiration occurs in the open stomata while reducing with the close

Translocation

• Translocation is process involving moving sugar from source to sink by pholem
• Sugars move from leaves (source) to roots (sink)
  • Sources: Parts that produce sugar
  • Sinks: Parts that receive
• It happens only with Active transport and companion cells

Digestive System

• Breaks down manageable prices for absorption and utilisation

Digestion Steps

• Ingestion: Taking in food via teeth, saliva, tongue, where teeth break down food and saliva enzymes breakdown
• Digestion: Occurs along the digestive tract where organs breakdown food
• Absorption: Molecules are absorbed across the plasma membrane, entering bloodstream
• Egestion: Removing undigested food

Mechaical/Chemical Digestion

• The mechanical way organs break down food to increase surface area for digestion
• Chemical molecules break down food for energy
• Occurs via Chewing stomach contractions, and segmentation
• Involves the saliva, stomach, emzymes
• Bile emulsifies large fatty molecules to small droplets

Digestion Organs

• Liver creates bile and send to gal bladder
• Gal Bladder contains bile for small intestine
• Pancreas adds the emzymes to neutralise acid

Alimentary Canal

• Mouth with teeth breaking food down
• The use of peristalsis through the Oesophagus
• Enzymes from Stomach increasing SA
• Small intestines: digestion and absorption by enzymes
• Large intestines compacting material back into the colon

Enzymes

• Breaking the molecules used in hydrolysis
• Proteins help chemical reaction
• They help reduce macromolecules
• Substance being acted on is a substrate
• Denatured enzymes can no longer be used, they detach via substrate
• Temperature and PH and Enzyme concentration can affect it

Excretory System

• Nephron: secreting waste and reabsorbing substances
• Removing excess components to maintain environment
• Remove excess ions and watre, remove dioxide, toxins etc

Filtration Structure

• Blood is filetered by Bowman's capsule
• Primary filtrates through Glomerulus membranes
• Proxymial tubule reobsorb Amino acids and other ions, toxing for osmosis
• Loop of Henle does reabsorption and secretion
• Distal tubule does filtration

Filtration: Blood is filtered in the glomerulus in the Bowman’s capsule.

Reabsorption: Water and nutrients reabsorbed

Secretion: Unwanted substances secreted into tubules.

URINE: moves from kidneys → ureters → bladder → urethra for elimination