Cell Biology

2 major divisions: Prokaryotic, Eukaryotic

• prokaryotic: simple cell, no nucleus, no membrane-bound organelles, nucleoid (has the genetic material), eg - bacteria, binary fission, only in Monera kingdom

• eukaryotic: complex, nucleus(control center), unicellular or multicellular, membrane-bound organelles, eg - plant and animal cells

organelles

prokaryotic

• plasma membrane - selectively permeable (made up of double layer of phospholipids)

• cell wall - wall/barrier, shapes and protects, in ALL prokaryotes

• ribosomes - host for protein synthesis, in the cytoplasm, has large unit and small subunit

eukaryotic

• ribosomes - host for protein synthesis, in the nucleolus

  • bound - attached to endoplasmic reticula, forms proteins that are exported from cell or sent to the membrane

  • free - exist freely in cytoplasm, forms proteins that remain in cytoplasm

• smooth endoplasmic reticulum (SER) - has no ribosomes on the surface = smooth, membrane bound, lipid synthesis, detox, carbs metabolism, a lot in liver bc thats where alcohol gets detoxed and carbs metabolized (glycolysis)

• rough endoplasmic reticulum - membrane bound, rough = ribosomes on surface, produces proteins that are secreted by the cell —> carried by vesicles to Golgi Apparatus

• Golgi Apparatus - like post office of the cell, macromolecules come —> Golgi modifies it by adding sugars, etc to form glycoproteins —> they get sent in vesicles to other parts of the cell based on their modifications/changes

• Mitochondria - powerhouse of the cell, energy produced (ATP)

  • matrix - inner part, hosts Krebs cycle

  • cristae - the folds, hosts oxidative phosphorylation of respiration

• Lysosome - stomach of the cell, suicide sac of the cell, gets rid of unneeded stuff like the tail of a tadpole when turning to a frog, digests/breaks down macromolecules, without it there are storage diseases like Tay-Sachs disease (too much accumulation of lipids in the brain)

• Nucleus - control center of the cell, has the nucleolus which is the site for ribosome synthesis, DNA storage site, RNA site for = replication, transcription, post-transcriptional modification

• Vacuole - vault, storage organelle, large in plant cells but small in animal cells

• Peroxisomes - has enzymes that create hydrogen peroxide as a by-product when doing other stuff like breaking down fatty acids, it also has enzymes that turn toxic hydrogen peroxide into cell-friendly water

• Chloroplast - colors leaves/pigmentation, site for photosynthesis and energy production in plants

  • outer portion - 2 outer membranes

  • inner portion - stroma (fluid part, light-independent/dark reactions occur here ) and the thylakoid membrane system (inner membrane through stroma, light-dependent reactions occur here)

• cytoskeleton - skeleton of cells, 3 fibers

  • microtubules - separation of cells/cell division, made of tubulin, part of cilia, flagella

  • microfilaments - muscular contraction, made from actin

  • intermediate filaments - reinforce shape and position of organelles, made of proteins called keratins

Fluid Mosaic Model

• membrane arrangement model

• cell membrane —> barrier around cell w/ phospholipid bilayer

  • outer portion - hydrophilic head

  • inner portion - hydrophobic tail

• integral proteins - implanted within bilayer, can extend partly or all the way across membrane

• peripheral proteins - ex: receptor proteins, not implanted in bilayer, attached to integral proteins

• selectively permeable - based on size and charge

  • small uncharged polar, hydrophobic (ex: lipids) can go through

  • large uncharged polar (ex: glucose), and charged ions (ex: sodium) cant go through

Types of cell transport

• Diffusion = no energy use, high concentration to low concentration, molecules move down their concentration gradient, the rate varies based on selective permeability

• Osmosis = no energy use, low concentration to high concentration, water moves down its concentration gradient (high concentration of water to low concentration of water), hypotonic to hypertonic

• Facilitated Diffusion = no energy use, particles diffuse across selective permeable membrane, uses the membranes transport proteins, it is specific (has binding sites for certain particles, not just any particle can do it)

• Active Transport = uses energy (ATP), particle moves AGAINST concentration gradient, low concentration to high concentration, used to maintain concentration, Ex: sodium-potassium pump —> cells have high concentration of K, low concentration of Na, the pump actively moves K in and Na out to keep these concentrations, this is a major pump in animal cells

• Endocytosis = substances are brought into cells, used by immune cells (phagocytes) to engulf and eliminate foreign invaders

• Exocytosis = like a trash chute of the cell, reverse of endocytosis, substances are exported from the cell

Cell Division

• binary fission - DNA —> duplicated —> elongated —> separated into 2 cells

• cell cycle - phases —> G1, S, G2, M

• G1, G2 = growth stages

• S = duplication

• M = mitosis, cell division

• G1 = prep for synthesis, has all the raw materials

• S = DNA copied

• G2 = prep for mitosis (production of body cells) and/or meiosis (production of gametes)

• M = Mitosis, split into 2 cells

• Mitosis - single cell uses for asexual reproduction, multicell uses for other stuff like growth and repair

• 4 stages —> prophase, metaphase, anaphase, telophase

• then cytokinesis (physical separation of daughter cells)

controls of cell division

• Checkpoints = verify if there are enough nutrients and raw materials to go to the next stage of the cycle

• Density-dependent inhibition = once the certain density is reached it slows or stops growth because it doesn’t have enough materials (the phase is called G0), cancer cells don’t have this so they grow out of control

• Growth factors = help with the growth of structures, if they are absent then some cells don’t divide

• Cyclins and Protein Kinases =

  • cyclin —> a protein that accumulates in G1, S, G2

  • protein kinase —> protein that controls other proteins by adding phosphate groups

  • CDK (cyclin-dependent kinases) bind with cyclin to form MPF (maturation/mitosis promoting factor)

  • early in the cycle the cyclin is low = MPF is low —> when cyclin concentration reaches a certain level = the MPF is enough to push the cell into mitosis —> as mitosis goes on = cyclin decrease = MPF decrease = pull out of mitosis

Haploid vs Diploid

• Haploid (n) has one copy of each type of chromosome

• Diploid (2n) has 2 copies of each type of chromosome

  • humans have 2 full sets of 23 chromosomes (1 from each parent)

Meiosis

• occurs during sexual reproduction

• goes through the cell cycle until G2 then it enter meiosis (2 cell divisions not 1)

  • the 2nd cell division exists because the gametes formed in meiosis need to be haploid because they join with another haploid gamete to make a diploid zygote

• 2 acts: Meiosis 1, and Meiosis 2 (each with 4 parts - prophase, metaphase, anaphase, telophase)

  • 1 - separation of the homologous pairs into 2 separate cells

  • 2 - separation of the duplication sister chromatids into chromosomes

• a single cycle produces 4 cells from a single cell

• the cells that are produced are called gametes