GENBIO-1STQTR-REVIEWER PDF - Cell Theory

CELL THEORY Theory of Spontaneous Generation Abiogenesis Proposed by Aristotle: life originated from non-living PROPONENTS IN BIOGENESIS matter. Appearance of animals from environments Francesco Redi previously devoid of such an...

CELL THEORY Theory of Spontaneous Generation Abiogenesis Proposed by Aristotle: life originated from non-living PROPONENTS IN BIOGENESIS matter. Appearance of animals from environments Francesco Redi previously devoid of such animals. Lazzaro Spallanzani o Flies can grow from animal manure Louis Pasteur o Fish in a new puddle of water 1. Francesco Redi o Frogs simply seem to appear along the - One of the first to refute the idea that maggots muddy banks of the Nile River in Egypt (the larvae of flies) spontaneously generate on during the annual flooding. meat left out in the open air. - He predicted that preventing flies from having PROPONENTS IN ABIOGENESIS direct contact with the meat would also prevent Jan Baptista Van Helmont the appearance of maggots. John Needham - Experiment: Redi left meat in each of 3 1. Jan Baptista Van Helmont containers. One was open to the air, one was - 17th Century Flemish Scientist covered with gauze, and one were tightly sealed. - Experiment: Place a dirty shirt or some rags in an - Observations: Maggots developed in the open pot or barrel containing a few grains of uncovered jars, but no maggots appeared in wheat or some wheat bran, and in 21 days, mice either the gauze-covered or the tightly sealed will appear jars. - Observation: There will be adult males and - Conclusion: Maggots could only form when flies females present, and they will be capable of were allowed to lay eggs in the meat, and that mating and reproducing more mice. the maggots were the offspring of flies, not the - Conclusion: Mice could arise from rags and product of spontaneous generation. wheat kernels left in an open container for 3 weeks (Redi refuted) 2. Lazzaro Spallanzani 2. John Needham - Experiment: Broth in sealed jars and unsealed - Experiment: He briefly boiled broth infused with jars was infused with plant and animal matter. plant or animal matter, hoping to kill all - Observation: Spallanzani’s results contradicted preexisting microbes. He then sealed the flasks. the findings of Needham: Heated but sealed - Observation: After a few days, he observed that flasks remained clear, without any signs of the broth had become cloudy and a single drop spontaneous growth, unless the flasks were contained numerous microscopic creatures. subsequently opened to the air. - Conclusion: The new microbes must have arisen - Conclusion: Microbes were introduced into spontaneously. In reality, however, he likely did these flasks from the air. Any subsequent sealing not boil the broth enough to kill all preexisting of the flasks then prevented new life force from microbes. entering and causing spontaneous generation  - While observing cork through his microscope, Hooke saw tiny boxlike cavities, which he illustrated and described as cells. 3. Anton Van Leeuwenhoek - He was the first to observe living cells under the microscope in 1674, paving the way for future discoveries. - He was able to observe living cells, living unicellular organisms (sperm, and protists). 3. Louis Pasteur These organisms looked like unicellular animals. - Experiment: Made a series of flasks with long, And he called them “animalcules “ twisted necks, in which he boiled broth to 4. Matthias Schleiden sterilize it. His design allowed air inside the flasks - In 1838, Schleiden proposed that all plants are to be exchanged with air from the outside, but made up of cells. prevented the introduction of any airborne - Schleiden studied and observed different plant microorganisms, which would get caught in the structures under the microscope and found that twists and bends of the flasks’ necks. plants are made up of cells. - Observation: Sterilized broth in his swan-neck - Schleiden published his finding in his work flasks would remain sterile as long as the swan entitled “Contributions to our Knowledge of necks remained intact. However, should the Phytogenesis.” necks be broken, microorganisms would be 5. Theodor Schwann introduced, contaminating the flasks and - His most significant contribution to biology is allowing microbial growth within the broth. considered to be the extension of cell theory to animals. - All animals are made up of cells. 6. Rudolf Virchow - In 1885, he proposed that omnis cellula e cellula: “all cell comes from another cell” The Fundamental Principles of Cell Theory 1. All living organisms are composed of one or more cells. 2. A cell is the basic unit of life of the structural Early Contributors of the Cell Theory organization of an organism. 3. Cells arise from pre-existing cells 1. Zacharias Janssen - Contributed with the invention of the single-lens MICROSCOPE microscope and that of multiple lenses Light Microscope (compound microscope) for cell discovery in the - Up to 1000x Magnification future. - Most subcellular structures, including organelles, 2. Robert Hooke are too small to be resolved by a light - Published Micrographia—a book that revealed microscope. the microscopic world. - Hooke was one of a small handful of scientists to Scanning Electron Microscope (SEM) embrace the first microscopes, improve them, and use them to discover nature’s hidden - Surface feature of the specimen providing details. images that look 3-D - He designed his own light microscope, which used multiple glass lenses to light and magnify specimens. Under his microscope, Hooke examined a diverse collection of organisms. Transmission Electron Microscope (TEM) - Have a nucleus enclosed within the nuclear membrane and form large and complex - Internal Structure of Cells organisms. - Protozoa, fungi, plants, and animals all have eukaryotic cells. - They are classified under the kingdom Eukaryota. - They can maintain different environments in a single cell that allows them to carry out various PROKARYOTIC AND EUKARYOTIC CELLS metabolic reactions. Cell Organelles Functions: - This helps them grow many times larger than the https://youtu.be/URUJD5NEXC8?si=o3QhHXycx60YRCY0 prokaryotic cells. Endomembrane System Protein Processing: https://youtu.be/tNEYtfvmRsc?si=LYgJKcKejyNulH3w Characteristics of Eukaryotic Cells Bacterial Structure and Functions: DNA in a nucleus that is bounded by a https://m.youtube.com/watch?v=b15Hy3jCPDs membranous nuclear envelope Basic features of all cells (Eukaryotic and Membrane-bound organelles Prokaryotic): Cytoplasm in the region between the plasma membrane and nucleus Plasma membrane Larger than prokaryotic cells Semifluid substance called cytosol Chromatin material (carry genes) Ribosomes (make proteins) Prokaryotic Cell - Rod-shaped Bacterium - Unicellular (One Cell) Characteristics of Prokaryotic Cells No nucleus DNA in an unbound region called the nucleoid No membrane-bound organelles Cytoplasm bound by the plasma membrane Prokaryotes are divided into two distinct groups: the bacteria and the archaea Structure Of Eukaryotic Cell Endomembrane System - is a group of membranes and organelles in eukaryotic cells that works together to modify, Eukaryotic Cell package, and transport lipids and proteins. a. Cell Membrane - Punctuated with pores that control the passage - Also called the plasma membrane separates the of ions, molecules, and RNA between the cell from the outside environment. nucleoplasm and cytoplasm - It comprises specific embedded proteins, which f. Nucleoplasm help in the exchange of substances in and out of - semi-solid fluid inside the nucleus, where we the cell. find the chromatin and the nucleolus g. Endoplasmic Reticulum - It is a network of small, tubular structures that divides the cell surface into two parts: luminal and extraluminal. - Endoplasmic Reticulum is of two types: i. Rough Endoplasmic Reticulum (RER)- Modifies newly synthesized protein from its lumen such as folding or addition of sugars. It also makes phospholipids for b. Cytoplasm cell membranes - Is the gelatinous liquid that fills the inside of a ii. Smooth Endoplasmic Reticulum (SER)- Is cell where synthesis of carbohydrates and - It is composed of water, salts, and various lipids happens. It is the storage of organic molecules. calcium ions and steroid hormones. And - Some intracellular organelles, such the nucleus where detoxification of medications and and mitochondria, are enclosed by membranes poisons happen. that separate them from the cytoplasm. h. Golgi Apparatus c. Cytoskeleton - It is made up of flat disc-shaped structures called - Is network of fibers extending throughout cisternae. cytoplasm. It organizes the cell’s structures and - It has receiving face near the endoplasmic activities. reticulum and a releasing face on the side away - Anchoring many organelles. It helps to support from the ER, toward the cell membrane. the cell and maintain its shape. - It is absent in red blood cells of humans and - It enables the cell to move in responses to sieve cells of plants. stimuli. - They are arranged parallel and concentrically - The cytoskeleton is present inside the cytoplasm, near the nucleus. which consists of microfilaments, microtubules, - It is an important site for the formation of and intermediate filaments to provide perfect glycoproteins and glycolipids. shape to the cell, anchor the organelles, and i. Ribosomes stimulate the cell movement. - These are the main site for protein synthesis and i. Microtubules - Is a small hollow tubes. It helps are composed of proteins and ribonucleic acids. the cell resist compression. It also pull replicated - It appears as clusters or tiny dots that float freely chromosomes to opposite ends of dividing cells. in the cytoplasm. ii. Microfilaments - Is the narrowest and function in - Can be found in the outer membrane of the cellular movement. It is made-up of two nuclear envelope, cytoplasmic side of the plasma intertwined strands of globular protein called membrane, cytoplasmic side of ER actin. j. Mitochondria iii. Intermediate filaments - It is made up of several - These are also known as “powerhouse of cells” strands of fibrous proteins and has no role in cell because they produce ATP energy. movement. It pulls replicated chromosomes to - This is where cellular respiration happens, opposite ends of dividing cell. wherein it uses oxygen and produces carbon d. Nucleus dioxide as a waste product. - The nucleus (plural = nuclei) houses the cell’s k. Lysosomes DNA and directs the synthesis of ribosomes and - A digestive component and recycling facility of proteins animal cells, considered part of the e. Nuclear envelope endomembrane system. - Encloses the nucleus, separating it from the cytoplasm  - a membranous sac of hydrolytic enzymes that s. Flagella can digest macromolecules. - Long hair-like structure used to move an entire - Contain lysosomal enzymes that can hydrolyze cell proteins, fats, polysaccharides, and nucleic acids - Short hair-like structures that are used to move as well as pathogens that might enter the cell. the entire cell l. Food Vacuole t. Cilia - Forms when some types of cell engulf another - Extend along the entire plasma membrane cell by phagocytosis - Short hair-like structures that are used to move - A lysosome fuses with the food vacuole and the entire cell digests the molecules m. Peroxisome TISSUE/CELLS TYPES - Small, round organelles enclosed by single Amoeba, euglena, paramecium, and e coli are membranes. examples of single-celled organisms. Bacteria are - It carry out oxidation reactions that break down prokaryotes while the rest are classified as fatty acids and amino acids. eukaryotes - These oxidation reactions release hydrogen Cells with the same structure and function are peroxide, H2O2, which would be damaging to grouped together to form tissues. cells Cells that line the retina of your eye, have a - When these reactions are confined to structure and function that is very different from peroxisomes, enzymes safely break down the your skin cells. H2O2 into oxygen and water. For example, Muscle cells tend to be long to allow for alcohol is detoxified by peroxisomes in liver cells. contraction. - Glyoxysomes, which are specialized peroxisomes Nerve cells tend to have many branches to help in plants, are responsible for converting stored with communication. fats into sugars Tissue Structure and Function n. Vesicles and Vacuoles - Membrane bound sacs that function in storage Epithelial and transport Connective - Vacuoles are larger than vesicles Muscle o. Centrosomes Nervous - Microtubule organizing center - Contains a pair of centrioles - Replicates before the cell divides - Pull the duplicated chromosomes to opposite ends of the dividing cell p. Cell Wall - Extracellular structure that distinguishes plant cells from animal cells - Protects the plant cell, maintains its shape, and 1. Epithelial Tissue prevents excessive uptake of water - Covers the outside of the body and lines the - Are made of cellulose fibers embedded in other organs and cavities within the body polysaccharides and protein - The main function of epithelial tissue are q. Chloroplast protection, secretion (producing and releasing - Contain a green pigment called chlorophyll. materials) and absorption (taking in materials). - Like plant cells, photosynthetic protists also have - Epithelia contain no blood vessels (they are non- chloroplasts. vascular) and are dependent upon the - Some bacteria perform photosynthesis, but their underlying connective tissue for nutrients. chlorophyll is not relegated to an organelle. - Types of Epithelial Tissue: r. Central Vacuole a. Cuboidal Epithelium - Plant cells have large central vacuole o dice shaped cells specialized for - Key role in regulating the cell’s concentration of secretion water in changing environmental conditions  o makes up the epithelium of kidney b. Elastic fibers - stretch and snap back to their tubules and many glands, including the original length. thyroid gland and salivary glands c. Reticular fibers - join connective tissue to b. Simple Columnar Epithelium adjacent tissues. o large, brick-shaped cells Loose Connective Tissue o often found where secretion or active - Binds epithelia to underlying tissues and absorption is important. holds organs in place. c. Simple Squamous Epithelium - Loose connective tissues gets its name o lines blood vessels and the air sacs of from the loose weave of its fibers, which the lungs, where diffusion of nutrients include all three types. and gases is critical - It is found in the skin and throughout the o single layer of plate-like cells body. o functions in the exchange of material by Bone diffusion - The skeleton of most vertebrates is made o thin and leaky of bone. d. Pseudostratified Ciliated Columnar - Bone-forming cells called osteoblasts Epithelium deposit a matrix of collagen. o consists of a single layer of cells varying Cartilage in height. - Contains collagenous fibers embedded in a o In vertebrates, it forms a mucous rubbery protein-carbohydrate complex membrane that lines portions of the called chrondroitin sulfate. respiratory tract. - Cells called chondrocytes secrete the o The beating cilia sweep the film of collagen and chondroitin sulfate. mucus along the surface. Adipose Tissue o It is also a part of respiratory tract that - Stores fat in adipose cells distributed sweeps unwanted particles e. throughout its matrix. e. Stratified Squamous Epithelium - Adipose tissue pads and insulates the body o multilayered and regenerates rapidly. and stores fuel as fat molecules. o commonly found on surfaces subject to Blood abrasion, such as the outer skin and the - Plasma, which consists of water, salts, and linings of the mouth, anus, and vagina. dissolved proteins. - Erythrocytes (red blood cells), Leukocytes (white blood cells), and cell fragments called Platelets. 2. Connective Tissues - Mainly binds and supports other tissues. - It contains sparsely packed cells scattered throughout an extracellular matrix. 3. Muscle Tissue - The matrix consists of fibers in a liquid, jellylike, - It is composed of cells that have the special or solid foundation. ability to shorten or contract in order to - Three types of connective tissue fiber, all made produce movement of the body parts. of protein: - It consists of long cells called muscle fibers, a. Collagenous fibers - provide strength and which contract in response to nerve signals. flexibility. - Types of Muscle Cells  a. Skeletal Muscle - or Striated Muscle, is PLANT CELLS/TISSUES attached to bones and is responsible for Plant Tissues: voluntary movement. https://youtu.be/_rw4bo809JE?si=gwEIqM1TAV7mZLus b. Smooth Muscle - mainly lines internal The Three Tissue Systems organs and is responsible for involuntary body activities. 1. The dermal tissue system provides a protective c. Cardiac Muscle - is responsible for cover. contraction of the heart. 2. The vascular tissue system, transports materials between the root and shoot systems 3. The ground system, responsible for the plant’s metabolic functions 4. Nervous Tissue - Senses stimuli and transmits signals throughout the animal. - Functions in the receipt, processing and transmission of information o Neurons - nerve cells that transmit nerve impulses - receives nerve impulses from other neurons via its cell body 1. Dermal Tissue System and multiple extensions called dendrites a. Epidermis cells - transmit impulses to neurons, - are modified to form stomata, openings in the muscles, or other cells via epidermis that regulate gas exchange in plants extensions called axons - Two specialized epidermal cells called guard o Glial cells or glia - that help nourish, cells regulate the diameter of the pore insulate, and replenish neurons - remodified to form trichomes that extend out from the plant - Epidermis - tissue that covers the plant on non woody part b. Trichomes - have glands that contain oil or other substances secreted by the plant - hairlike outgrowths of the shoot epidermis. - in some species – reduce water loss and reflect excess light - Main function to provide defense against insects by secreting sticky substances c. Periderm - Cork/Bark - Tissue that covers the plant on woody part of the cell - Dead cells  - consists of multiple layers of cells, including SPECIALIZED CELLS outer layers of protective cork cells and typically Cell Specialization and Differentiation: thin inner zones of living cells. https://youtu.be/LNLz7mswPkQ?si=0op8BEJFEzFWFy57 2. Vascular tissue system - Cell specialization is vital for proper embryo development. The embryo needs cells to develop a. Xylem each of its vital organs, such as the brain, heart and - conducts water and dissolved minerals upward skin. from roots into the shoots. - The types of xylem cells: vessel elements and tracheids. - The main conducting cells are the VESSEL ELEMENTS, which are dead cells at maturity that lack a plasma membrane b. Phloem - transports sugars, the products of photosynthesis c. Sieve tube cells - also called sieve tube members or sieve elements - make up the main structure of phloem. - These cells are narrower and have pitted ends Egg Cell resembling small sieves. The female sex cell. - Each sieve tube cell is connected via a series of They are made in the ovaries and released pores to a nucleated during the menstrual cycle. - companion cells direct the functions of the sieve An egg cell joins with the sperm cell during tube element. fertilization to make an embryo. 3. Ground Tissue System The nucleus contains a genetic material. The cytoplasm contains nutrients for the embryo - fills in the spaces in the plant body between the to grow. dermal and vascular tissues. - includes cells specialized for storage, Sperm Cell photosynthesis, and support a. Parenchyma Cells The male sex cell - are the most abundant kind of plant cell. The head of the sperm contains the genetic - found throughout the tissues of a plant cell. material for fertilization. - usually have a large central vacuole, which The acrosome in the head contains enzymes so contains a fluid called sap that the sperm can penetrate an egg. b. Collenchyma Cells The middle piece is packed with mitochondria to - long cells unevenly thickened cell walls release energy needed to swim and fertilize the - walls of collenchyma cells can stretch as the egg. cells grow while providing strength and The tail enables the sperm to swim. support Muscle Cells c. Sclerenchyma Cells - very thick and rigid. Striated or striped appearance - At maturity, these cells often die leaving More mitochondria than many other body cell strong, thick cell walls that provide support types for the plant Have intercalated disks Red Blood Cells Biconcave - dented on both sides Gives the cell a larger surface area to absorb more oxygen  They are also flexible which are helpful when - Binary fission, a kind of mitotic division, is used in squeezing through capillaries unicellular organisms for reproduction. When they are mature, they don’t have nucleus - Multicellular organisms depend on cell division for: or organelles to maximize space. o Reproduction They also contain hemoglobin in their cytoplasm o Growth and Development which is a protein that help them carry oxygen. o Repair Nerve Cell Tissue renewal – dividing bone marrow cells will give rise to new blood cells. The nerve cell are extended, so that nerves can run to and from different parts of the body to Mitosis the central nervous system. It is the process by which a cell replicates its The cells has extensions and branches, so that it chromosomes and then segregates them, producing two can communicate with other nerve cells, identical nuclei in preparation for cell division. muscles, and glands. The nerve cell is covered with a fatty The cell cycle consists of: sheath/myelin sheath, which insulates the nerve o Interphase (cell growth and copying of cell, and speeds up the nerve impulse. chromosomes in preparation for cell division) Root Hair Cells o Mitotic (M) phase (mitosis and cytokinesis) The cytoplasmic extensions increase the surface are for water absorption. It has thin walls so as not to restrict the movement of water Guard Cells Cell wall around the stoma is much thicker Help to regulate the rate of transpiration by opening and closing the stomata. Trichomes Can secrete toxic substances to protect against insects that might want to eat the plant. Some act like light reflector to help protect plant that live in really hot area. Palisade Cells More chloroplast in palisade cells. For absorption of light so that photosynthesis will take place. CELL CYCLE Interphase Cell Cycle: G1 Phase (First gap phase) https://youtu.be/e6N9_RhD10Q?si=YJ83l9mL92noZgjW https://youtu.be/5bq1To_RKEo?si=T3jiFjfOqAs8ypXL - The cell grows physically larger - Produce extra organelles, ribosomes, Interphase checkpoints: mitochondria, ER and proteins https://youtu.be/VLJF8Pf8spw?si=_7kxZKPTl2l7T-xy - Major period of cell growth and normal cell - Cell Division is the ability of organisms to reproduce functioning best distinguishes living things from nonliving matter. S phase - The continuity of life is based on the reproduction of - In S phase, the cell synthesizes a complete copy cells, or cell division of the DNA in its nucleus. o In unicellular organisms, division of one cell - It also duplicates a microtubule-organizing reproduces the entire organism structure called the centrosome.  - The centrosomes help separate DNA during M Kinetochore - Where the spindle fibers attach phase. during cell division to pull sister chromatids G2 phase (Second Gap phase) apart. - The cell grows more, makes proteins and Duplicated Chromosomes - Chromosomes that organelles have been duplicated will have two sister - Begins to reorganize its contents in preparation chromatids attached to the same centromere. for mitosis. Sister Chromatid - They have identical genetic - G2 phase ends when mitosis begins. information. Mitotic Phase is conventionally divided into five phases: - The sequential events of the cell cycle are Prophase directed by a distinct cell cycle control system, Prometaphase which is similar to a clock. Metaphase - A checkpoint is a stage in the eukaryotic cell Anaphase cycle at which the cell examines internal and Telophase external cues and "decides" whether or not to a. Prophase move forward with division. - Chromosomes condense and become visible. - If a cell receives a go-ahead signal at the G1 - Nuclear envelope Disappears. checkpoint, it will usually complete the S, G2, - Centrioles move to the poles of the cells. and M phases and divide. - Spindle Fibers begin to extend from the poles. - If the cell does not receive the go-ahead signal, it b. Prometaphase will exit the cycle, switching into a nondividing - The transition stage from prophase to state called the G0 phase. metaphase. - Most cells of the human body are actually in the c. Metaphase G0 phase. - Chromosomes line up along the equator (center G1 checkpoint of the cell). - Spindle fibers attach to the centromeres of each - The G1 checkpoint occurs at the G1/S transition chromosomes. of the cell cycle. d. Anaphase - Cell size, nutrient availability, molecular signals - Spindle fibers shorten pulling the chromosomes (such as growth factors). poles. - Cell’s DNA is checked if damaged. - Sister chromatids separate at the centromere G2 checkpoint and move to the poles. e. Telophase - The G2 checkpoint occurs at the G2/M transition - Chromosomes uncoil and become invisible. of the cell cycle. - Nuclear envelope reappears. - Cell’s DNA is checked. - Spindle fibers disappears. - If damage to DNA are detected, will pause at G2 - Occurs simultaneously with cytokinesis. to allow for repairs - Daughter cells have identical genetic - Cells undergo apoptosis information. f. Cytokinesis M checkpoint (spindle checkpoint) - Separation of the cell and cell contents. - Occurs between metaphase and anaphase of (Cytoplasm ~ Organelles ~ Cell Membrane) mitosis. - Does not have to be an equal division. - Chromosomes must be properly attached to the - Daughter cells can be different sizes and have mitotic spindle at the metaphase plate. cellular content but nucleus is the same. Chromatin - The unwound form of the Two types of regulatory proteins are involved in cell cycle chromosome. control: cyclins and cyclin-dependent kinases (CDKs) Condensed - Condensation occurs at the beginning of cell division. Internal Regulator Checkpoints - Where the cell checks to make - proteins and other molecules within the cell sure it is able to proceed to the next phase.  - help divide at the correct rate and under the right - DNA replication – to make duplicated conditions. chromosomes - allow the cell cycle to move forward only after - Cell does not change structurally certain events inside the cell have taken place. - Two important regulators in the cell cycle control Prophase I system are cyclins and cyclin-dependent kinases - Replicated chromosomes have coiled and are (CDKs). already visible. a. Cyclins - Homologue chromosomes begin to pair and - are proteins that are synthesized (made) and twist around each other in a highly specific broken down at specific times during the cell manner. cycle, which causes their levels to rise and fall at - Chromosomes become much shorter and different points in time thicker. b. Cyclin –dependent kinases (CDKs) - A form of physical exchange between - are enzymes that interact with specific cellular homologues takes place at specific regions called components related to the cell cycle. crossing-over. - area of contact between two non-sister Cyclins regulate the cell cycle only when they are tightly chromatids, called chiasma, become evident. bound to CDKs. Without a specific concentration of fully - Synapsis - the pairing of homologous activated cyclin/CDKs complexes, the cell cycle cannot chromosomes proceed through the checkpoints - Group of four chromatids - homologous External regulators chromosomes (each with sister chromatids) to - are signals from outside the cell. join to form a tetrad. - help regulate the cell cycle based on - Crossing over - homologous chromosomes in environmental conditions and other external tetrad cross over each other and genes are factors. exchanged. Meiosis Metaphase I A type of cell division in sexually reproducing organisms - The spindle apparatus is completely formed. that reduces the number of chromosomes in gametes - The microtubules are attached to the (the sex cells, or egg and sperm). In humans, body (or centromere. somatic) cells are diploid, containing two sets of - The synapsed tetrads are found aligned at the chromosomes (one from each parent). metaphase plate. Anaphase I - Chromosomes in each tetrad separate and migrate toward the opposite poles. - The sister chromatids (dyads) remain attached at their respective centromere regions Telophase I - Nuclear envelope reappear - Spindle fibers disappear - Cytokinesis (when the cytoplasm divides) divides cells into 2. Cytokinesis - Duplicated chromosomes have The Stages of Meiosis - reached to poles - A nuclear envelope & nucleolus Interphase - re-forms around chromosomes. - Cell build up energy - Each nucleus now has the haploid number of chromosomes. Division in meiosis II also occurs in four phase: - Diseases linked to mosaicism – hemophilia, Marfan syndrome Prophase II - Cancer Metaphase II Anaphase II Error in Meiosis Telophase II Cytokinesis Meiosis II is very similar to mitosis Prophase II - Chromosomes coil and become compact (if uncoils after telophase I) - Nuclear envelope and nucleolus, if reformed it disappears again. - Centrioles move to opposite poles, forming spindle fibers between them Metaphase II - Individual duplicated chromosomes align on the equator. - One chromosomes per spindle fiber attached by means of kinetochore of centromere - Centrioles has reached the poles Anaphase II CELL MEMBRANE - Centromeres separate - Two chromatids of each chromosome move to Structure and Functions: https://youtu.be/fJfTDc3WzQ8?si=RxXZEeKiNcxOUl6z opposite poles on the spindle - Separated chromatids are now called Structure and Function chromosomes in their own right The cell membrane is a biological membrane Telophase II that separates and protects the interior of a cell from the outside environment - Daughter chromosomes has reached the poles A boundary, barrier, semi-permeable, and fluid - Two cells invigilate and form four daughter mosaic haploid cells (gametes) - They uncoil & form chromatin - Nuclear envelope and nucleolus for around chromatin again. Centrioles for centrosome Result of Meiosis - Gametes are formed - Four haploid cells with one copy of each chromosome - One allele of each gene - Different combinations of alleles for different genes along the chromosome Error in Mitosis - nondisjunction of chromosomes or sister Function chromatids - Mosaicism –passing the mutation through - Isolate’s cell’s content from outside mitosis environment.  - Regulate exchange of substances between - The temperature will affect how the inside/outside the cell. phospholipids move and how close together - Communicate with other cells they are found. When it’s cold they are found - Create attachments within/between cells closer together and when it’s hot they move - Regulate Biochemical reactions farther apart. The fluid mosaic model states that a membrane 2. Cholesterol is a fluid structure with a “mosaic” of various - The cholesterol molecules are randomly proteins embedded in it. distributed across the phospholipid bilayer, helping the bilayer stay fluid in different Components of Cell Membrane environmental conditions. Lipids (Phospholipids and Cholesterol) - The cholesterol holds the phospholipids together Proteins so that they don’t separate too far, letting Carbohydrate Groups unwanted substances in, or compact too tightly, restricting movement across the membrane. 1. Phospholipids - Without cholesterol, the phospholipids in your - Most abundant lipid in the plasma membrane cells will start to get closer together when - Phospholipids are amphipathic molecules, exposed to cold, making it more difficult for containing hydrophobic and hydrophilic regions. small molecules, like gases to squeeze in - Non-Polar - Not Charged Molecule between the phospholipids like they normally - Polar - Charged Molecule do. Without cholesterol, the phospholipids start to separate from each other, leaving large gaps. 2. Proteins 3. Saturated and unsaturated fatty acids - The cell is made up of two different types, or “classes”, of proteins: - Fatty acids are what make up the phospholipid - Integral proteins/Trans Membrane are nestled tails. into the phospholipid bilayer and stick out on - Saturated fatty acids are chains of carbon atoms either end. that have only single bonds (C–C) between - Are helpful for transporting larger molecules, like them. As a result, the chains are straight and glucose, across the cell membrane. easy to pack tightly. - The other class of protein is called peripheral - Unsaturated fats are chains of carbon atoms that - proteins, which don’t extend across the have double bonds between some of the membrane. carbons (C=C). - They can be attached to the ends of integral Small, nonpolar molecules (e.g. oxygen and proteins, or not, and help with transport or carbon dioxide): These molecules can pass communication. through the lipid bilayer and do so by squeezing through the phospholipid bilayers. They don't 3. Carbohydrates need proteins for transport and can diffuse across quickly. - another lipid composed of four fused carbon Small, polar molecules (e.g. water): not easy for rings, is found alongside phospholipids in the the water molecules to cross, but they can cross core of the membrane. without help of proteins. This is a somewhat Membrane Fluidity slower process. Large, nonpolar molecules (e.g. carbon rings): Cell membrane fluidity is the property of the cell These rings can pass through but it is also a slow membrane that allows it to adapt its shape process. and movement to different conditions. Large, polar molecules (e.g. simple sugar - Three key factors influence cell membrane glucose): The size and charge of large polar fluidity: temperature, cholesterol, and the kind molecules make it too difficult to pass through of fatty acids in the phospholipids that form the the nonpolar region of the phospholipid cell membrane. membrane without help from transport proteins. 1. Temperature 4. Ions (e.g. NA+)  - The charge of an ion makes it too difficult to pass - Can change their shape to move a target through the nonpolar region of the phospholipid molecule from one side of the membrane to the membrane without help from transport proteins. other. Active Transport Cell transport is the movement of substances - Moves substances against their concentration (salt, nutrients, proteins) across the cell gradient. membrane either into or out of the cell. - Active transport requires energy, usually in the Concentration is the amount of solute in the form of ATP (Adenosine Triphosphate). solution. - It is performed by specific proteins embedded in Example: high concentration is a high amount of the membrane. solute in a solvent. The sodium-potassium pump: a specific case of active transport CELL TRANSPORT MECHANISM - This transport system pumps ions against steep (big difference in) concentration gradients. Transport: https://youtu.be/ufCiGz75DAk?si=HO8_Mxijpn7EPsld - Sodium ion concentration ([Na]) is high outside Diffusion: the cell and low inside, while potassium ion https://youtu.be/lxHMJaXOzP4?si=HgBrPCI2yWXa3TJw concentration ([K]) is low outside the cell and high inside. Transport Proteins - Channel proteins called aquaporins facilitate the OSMOSIS passage of water. https://youtu.be/vCJVXYmXkzM?si=Ye6K5xA_oySTot_i Diffusion and Passive Transport Is the diffusion of water across a selectively permeable membrane. Diffusion is the tendency for molecules to spread Water diffuses across a membrane from the out evenly into the available space. region of lower solute concentration to the In the process of diffusion, a substance tend to region of higher solute. concentration. move from an area of high concentration to an Sugar molecules cannot pass through the area of low concentration until its concentration selectively permeable membrane. becomes equal throughout a space. Water diffuses from the solution with less Substance diffuse down their concentration concentrated solute to that with more gradient (1 particle is greater than the other), concentrated solute. the difference in concentration of a substance The diffusion of water, or osmosis, equalizes the from one area to another. sugar concentrations on both sides. The diffusion of a substance across a biological membrane is passive transport because it requires no energy from the cell to make it happen. Facilitated Diffusion - In facilitated diffusion, molecules diffuse across the plasma membrane with assistance from membrane proteins, such as channels and Water Balance of Cells Without Cell Walls carriers. Tonicity is the ability of a solution to cause a cell Channel Proteins gain or lose water. - Provide corridors that allow a specific molecule Isotonic Solution or ion to cross the membrane. Solute concentration is the same as that inside Carrier Proteins the cell; no net water movement across the plasma membrane. Hypertonic Solution In phagocytosis, a cell engulfs a particle in a vacuole Solute concentration is greater than that inside The vacuole fuses with a lysosome to digest the the cell; cell loses water. particle. Hypotonic Solution A ligand is any molecule that binds specifically to a receptor site of another molecule. Solute concentration is less than that inside the In receptor-mediated endocytosis, binding of cell; the cell gains water. ligands to receptors triggers vesicle formation. - Hypertonic or Hypotonic environments create osmotic problems for organisms. - Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments. - The protist Paramecium, which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump. Water Balance of Cells with Cell Walls - Cell walls help maintain water balance. - A plant cell is a hypotonic solution that swells until the wall opposes uptake; the cell is now turgid (firm). - If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cells become flaccid (limp). Bulk transport across the plasma membrane occurs by exocytosis and endocytosis - Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins. - Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles. - Bulk transport requires energy. Exocytosis - In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents. - Many secretory cells use exocytosis to export their products. Endocytosis - In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane. - Endocytosis is a reversal of exocytosis, involving different proteins. - There are three types of endocytosis: 1. Phagocytosis (“cellular eating”) 2. Pinocytosis (“cellular drinking”) 3. Receptor-mediated endocytosis