Cell Division & Development

• Unicellular organisms have cell division for reproduction
• Cells divide and multiply, which means they reproduce
• Multicellular organism cell division is for development to repair damaged or undeveloped cells
• Growth in multicellulars comes from a fertilized egg to an individual

Cell Cycle

• The cell cycle has two phases: interphase and mitotic phase
• Interphase happens "in between cell divisions," and consists of a long growth period
• In humans, a cell cycle takes 18-24 hours
• G1 (First Gap) is the primary growth period for cells
• Organelles develop and cytoplasm size grows here, taking 5-6 hours
• Synthesis duplicates DNA and grows slowly between 10-12 hours
• G2 (Second Gap) prepares for division, growing slowly and double checking everything to be perfect for M phase, taking 4-6 hours
• Chromatin condenses into chromosomes during G2
• G0 (Non-dividing) is either permanent or temporary
• Cells wait until they reach the right size in G0, during which cells can stop dividing

DNA and Replication

• Replication copies the cell's DNA before cell division
• DNA makes DNA
• Transcription is the coding message of a single gene carried out to the nucleus
• DNA makes RNA
• Translation is the process of converting the coded message from RNA into protein
• RNA makes protein
• Not all cells divide at the same rate
• Internal surveillance and control mechanisms regulate cell reproduction
• There are several checkpoints, key checkpoints that act like police that can say go or stop.
• A "go" signal is needed in order for the cell cycle to proceed
• G1 checkpoint checks if the cell is damaged or growing well
• G2 checkpoint checks that if the cell was replicated properly, a programmed cell death will initiate if replication was not proper
• M checkpoint checks if the spindle fibers are attached properly to the kinetochore
• Outside influences and hormones can modify the cell cycle
• Apoptosis is programmed cell death that occurs when a cell doesn't pass checkpoints

Additional factors

• Growth factors and the presence of other cells
• Mitosis and meiosis happen in the mitotic/M Phase, where PMAT and cytokinesis also happen
• Mitosis happens in somatic cells for repair and reproduction
• It generates new diploid cells (2n), which have two chromosome sets from parent cells
• 2(23)=46 diploid cells
• Asexual reproduction
• Nuclear division includes mitosis and cytokinesis
• Daughter cells are genetically identical to parent cells

Meiosis information

• Occurs in sex cells in testes and ovaries for purposes of reproduction
• Generates (1n), or 1 set of long chromosomes, or 1(23)=23 chromosomes
• Daughter cells are genetically different from parent cells due to crossing over, so it has 2 cell divisions, PMAT 1 and PMAT 2
• Meiosis 1 involves 1 diploid cell dividing into 2 haploid cells, which includes crossing-over
• Meiosis 2 involves 2 haploid cells dividing into 4 haploid cells

Chromosome Structure

• Chromatin are single, but not ready yet
• Chromatids are single, but more ready
• Chromosomes are relations between the two
• Chromatin/chromatid are exclusive to each other

Mitosis

• Centrosomes organize microtubules, which form mitotic spindles that pull chromosomes apart
• Asters stabilize centrosomes

Mitosis Phases

• Prophase consists of chromatin condensing into chromosomes
• Centrioles travel to different places as centrosomes migrate to different cell poles
• Centrioles are the middle of the centrosome, and spindle fibers latch onto them
• Prometaphase consists of the nuclear envelope fragments becoming visible
• Each chromatid has a kinetochore, or an attachment site of spindle fibers
• Metaphase aligns chromosomes via the midline and checks where the M checkpoint happens
• Anaphase consists of centromeres dividing as chromosome divides into two, which then travel to opposite poles
• Microtubules pull centrometers into the poles

Final Phases

• Telophase includes reformating nuclear envelope which reloads it into chromatin
• Spindle fibers disappear with the appearance of cleavage
• Cytokinesis is the division of cytoplasm, separating it and leaving a daughter cell
• Crossing-over is when sister chromatids exchange segments, creating genetic variability
• Prophase 1 condenses chromosomes

Meiosis details

• Homologous chromosomes pair up, creating genetic variability from crossing-over
• Multiple combinations can occur with the genetic variability
• Metaphase I aligns them at the midline, where crossing-over happens
• Anaphase I includes microtubules pulling centromeres into opposite poles
• Telophase I reforms the nuclear envelope, and cleavage appears
• Cytokinesis divides the cytoplasm and the cleavage disappears
• Prophase II includes duplication of centrioles as they travel to opposite poles
• The nuclear envelope disappears with the attachment of spindle fibers to chromosomes
• Homologous chromosomes are pairs of maternal and paternal chromosomes
• The synaptonemal complex is the zipper like structure that holds homologs to one another
• Synapsis is the association of nonsister chroma segments, and chiasmata is the point of crossing-over

Final cell cycle

• Metaphase II aligns in the middle
• Anaphase II includes microtubules pulling centrometers into opposite poles
• Telophase II gets a nuclear envelope
• Cytokinesis II divides cytoplasm into 2, and cleavage disappears leaving 4 daughter cells

Human Life Cycle

• Gametogenesis initiates with the eggs of the ovaries from females
• After oogenesis, only 1 egg cell is viable; and there are 4 cells, but only one is produced
• Stem cells are undifferentiated (with no job yet)
• In spermatogenesis, there are 4 sperm cells and there is quantity over quality

Egg and Sperm

• Tails of sperm are whiplike movements that propel the sperm
• Mid pieces contain mitochondria which produce energy for the sperm
• Heads contain chromosomes
• Acrosome contain enzymes to assist in fertilization
• Madaming sperm is needed because of the environment of the cervix, needing a perfect sperm for fertillization
• Zona pellucida is an outer shell that sperm must penetrate

Early Phase

• In the early embryonic stage, eggs and sperm form through gamete formation, and fertilization occurs when sperm and egg fuse plasma membranes together
• Nuclei fuse with one nucleus to form a zygote
• Cell division carves up different regions of egg cytoplasm for daughter cells
• This is the reproduction part of cell division
• Cell divisions, migrations, and rearrangements form 2-3 primary tissues
• This process starts the production of specialized organs called formation of germ layers
• Cell differentiation is when a stem cell changes from one type to a specialized type
• Organ formation is sculpted into organs and tissues
• Growth, tissue specialization, occurs, growing the organs in size

Human Embryonic Development

• Day 0 means both gametes are unicellular
• An egg cell joins with a sperm cell
• Day 1-2 is the first cleavage furrow extending between 2 polar bodies
• Day 3 is after the 3rd cleavage, cells form a compact ball
• Day 4 consists of a ball of 16-32 cells by 96 hours
• This is the morula, which is formed from the zygote
• Cells of the surface layer will function in implementation to form a membrane, which is the chorion
• Day 5 consists of fluid-filled cavities that form in the morula
• At the 32 cell stage, differentiation is occurring in the inner cell masses that will form the embryo
• This embryonic stage is called the blastocyst
• The blastocyst is on its way to the uterus, or a cluster of cells and an early stage embryo
• The blastocyst develops from morula and secretes Human Chronic Gonadrotopin (HCG), which serves as an indicator for pregnancy

Implantation Time

• Days 6-7 consist of the blastocyst's surface cells attaching themselves to the endometrium and starting to burrow into it
• Implantation into the uterine wall has started
• The blastocyst consists of trophoblast surface epithelium, blastocel-cavity, inner cell mass, which is a small clump of cell where the embryo will develop
• Ectopic pregnancies happen when the cell doesn't get implanted within the uterine tube within 6-7 days
• Cleavage (Day 4) is when cell division converts the zygote into a ball of cells
• It is a cytokinesis part
• A series of cell divisions in Day 4 of fertilization happens without growth or differentiation in the morula 16 cell stage
• The first division is roughly completed after 30 hours, or 18-36 hours after fertilization during a 10-12 hour interval
• A blastomere is each new cell
• Gastrulation is on Day 5 and consists of the product of early development that produces 3 germ layers

Gastrulation Details

• These germ layers consist of 3 primary tissues that form an early embryo
• 16 cells from morula will be distributed to the germ layers
• These germ layers consist of Ectoderm, mesoderm, and endoderm
• Cell differentiation means newly formed cells become specialized for a certain function
• These vary by shape and function in accordance to cell type, but have the same DNA
• Environmental factors where stem cells become specialized make cells different from others
• Morphogenesis is when specific organs and tissues begin to form
• Implantation takes place during Day 6-7
• It means the blastocyst implants into the uterine wall in phases of apposition where the blastocyst contacts the implantation site of the endometrium
• Adhesion is when trophoblast cells of the blastocyst attach receptive endometrial epithelium
• Invasion is when invasive trophoblast cells graft off the endometrial epithelial basement and invade

Cloning Explained

• Cloning is a copy of an entire organism
• Reproductive cloning requires a completely undifferentiated cell as the starting point
• Undifferentiated cells have not developed into a specialized function

Cloning Methods

• Embryo splitting and 8 cells
• Clones produced are genetically identical to each other but are not exact copies of each parent
• An egg is fertilized in vitro and allowed to divide to the 8 cell stage
• In vitro means outside the living organism
• Cells are separated and implanted into different surrogate mothers
• Each cell will develop producing an organism identical to each other, but not the parents

Cell Cloning

• Somatic cell nuclear transfer produces an identical clone of the parents
• Ian Wilmut created this procedure, resulting in Dolly the sheep
• Procedures involve somatic cells and egg cells to yield a true clone of an adult organism
• Diba kukuna ka muna ng egg coll tapar tatanggalin mo yong nucleus dun tapar you rakt a somatic coll tapar kukunin mo yong nucleus dun tapar lalagay mo na ngayon sa empty egg cell tapar iimplant riya sa rurvogate mother tapar magyiyield yon ng truc clone ng adult organism

Differentiating methods

• Embryo uses SCNT
• Using sperm cell
• True clones mean identical siblings

Therapeutic Cloning

• Inovles stem cell therapy and cloning of human cells to treat patients by creating new cells, tissues, & organs from human cells

Cancer Cells

• Cancer cells consist of the loss of control in cell division & differentiation
• Tumor = neoplasm -> new growth

Kinds of Tumors

• Benign tumors are a safer type and contained in one area that can enlarge but can't move
• Starts when a cell becomes genetically altered and starts to divide more than usual
• They do not penetrate the innermost part of the tissue
• Malignant tumors are genetically there with something that makes it moreactive.
• This leads to cancer that will stay in place, or in situ cancer
• If cancer penetrates other cells it is not cancerous
• In vitro cancer is cancer that stays in one place
• If nagpenetrate nasiya pwede na siya mag metastars, where "metastas" means a different place
• Once that happens, it becomes hyperactive
• The cancer can no longer be destroyed by surgery

Characteristics to consider

• It invades normal tissue and may produce secondary tumors while undergoing additional changes, this has the additional change of being able to invade surrounding tissue

Dysplasia vs Hyperplasia

• It is cancer when the cell loses organization, structure, & regulation
• Dysplasia involves abnormal structural change in shape when the nucleus is expanded
• Cytoplasm decreases in size, and cells lose specialized functions
• This suggests that tumors are precancerous
• Hyperplasia leads to continuous uncontrolled growth
• Insitu means it stays in one place, while metastasis spreads to different locations
• Dysplasia changes in shape while hyperplasia has continuous growth

Cares

• Genetics, if you have a family history of cancer
• Environmental factors, carcinogens, viruses, and bacteria
• HPV is found in females but can be prevented through vaccines; it is transferable through female and male
• HIV can affect cell regulation
• Epstein Barr (Herpes) afflicts cell regluation
• Diet and Lifestyle: If nagiextrove, or lifestyle factors are not implemented well
• Internal factors include immune system, Protooncogenes, genes important to call regulation

Diagnosis

• The doctor can diagnose cancer via X-ray, CT Scan (pricey), Ultrasound, PET Scan (for the brain), and MRI.

Explore cell division, the cell cycle phases such as G1 and G2, and DNA duplication. Learn about the key distinctions between cell division in unicellular and multicellular organisms. Discover gastrulation, reproductive cloning, and cellular differentiation.