[BIO101 _ QUIZ MAKER] L5 TO L7.pdf

ORGANIZATION OF CHROMOSOME ★ All the DNA in a cell constitutes the cell’s genome ★ A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) ★ DNA molecules in a cell are packaged...

ORGANIZATION OF CHROMOSOME ★ All the DNA in a cell constitutes the cell’s genome ★ A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) ★ DNA molecules in a cell are packaged into chromosomes More details... ➔ Chromosomes fit into the nucleus through an elaborate, multilevel system of packing. CHROMOSOME 3D [ 📷 VIDEO NOTES | How is DNA Packaged] ★ The process starts with assembly of a nucleosome which is formed when 8 separate histone protein subunits attach to the DNA molecule. ★ The combined tight loop of DNA and protein is the nucleosome ★ Multiple nucleosomes are coiled together and these then stack on top of ➔ Unfolded chromatin resembles beads each other. on a string, with each “bead” being a ★ The end result is a fiber of packed nucleosome, the basic unit of DNA nucleosomes known as a chromatin. packaging. ★ This fiber, which at this point is ➔ The nucleosome can be further folded condensed to a thickness of thirty to produce the chromatin fiber. nanometers is then looped and further packaged using other proteins which are not shown here. ★ This remarkable multiple finding allows six feet of DNA to fit into the nucleus of each cell in our body. ★ An object so small that ten thousand nuclei could fit on the tip of a needle. ★ The end result is that the DNA is tightly ➔ Eukaryotic chromosomes consist of packed into the familiar structures we chromatin, a complex of DNA and can see through a microscope, protein that condenses during cell chromosomes. division. Chromatin fibers are coiled ★ It is important to realize that and condensed to form chromosomes. chromosomes are not always present. The chromatin undergoes further They form only when cells are dividing. condensation to form the ★ At other times as we can see here at chromosome. the end of cell division, our DNA becomes less highly organized STRUCTURE OF CHROMOSOME ➔ In preparation for cell division, DNA is replicated and the chromosomes condense. ➔ Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome), attached along their lengths by cohesins. ➔ The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached. Haploid ➔ one set of chromosomes ➔ In humans, n=23 chromosomes ➔ Can be found in gametes (sex cells) – reproductive cells Diploid ➔ Two sets of chromosomes ➔ In humans, 2n = 46 chromosomes ➔ Can be found in somatic cells (body ➔ During cell division, the two sister cells) – non reproductive cells chromatids of each duplicated chromosome separate and move into two nuclei. 📷 [ VIDEO NOTES | What are Haploid and Diploid Cells ] ➔ Once separate, the chromatids are ★ These terms describe the number of called chromosomes. sets of chromosomes in a cell. ★ Haploid ○ A cell has only one set of chromosomes ○ Gametes (sex cells) have a haploid number of chromosomes (n) ○ In humans, every gamete has 1 set of 23 chromosomes. (n) = 23 ★ Diploid ○ A cell contains two sets of chromosomes ○ The union of gametes during fertilization creates a diploid cell called a zygote 2n = 46 (23+23) ○ At fertilization, the chromosomes from each parent match up to become the new pairs of chromosomes in a zygote TIG-ISA SILA: Each pair contains 1 chromosome from the father, and a corresponding Haploid vs Diploid chromosome from the mother. These pairs are called Homologous Chromosomes ○ Homologous Chromosomes only only uses SImilar in shape and gametes size along with the ○ A same types of genes in diploid the same locations. cell ○ A diploid zygote will go through underg cell division many times to oes two produce all the cells in the cell body of a fully developed baby. division All body cells except s to gametes are referred produc to as somatic cells. e4 Somatic Cells genetic Human ally somatic cells differen are always t diploid written haploid as 2n which gamet means they es have 2 sets of 23 chromosomes for a total of 46 chromosomes. Other organisms have somatic cells with different diploid numbers of chromosomes, but the HAPLOID DIPLOID gametes in these 1 set of 2 sets of organisms are chromosome chromosome haploid s; ½ diploid s; 1 set from ○ Always have number each parent half the No Contain pairs diploid homologous of numbe pairs homologous r of chromo “N” chromosome somes. chromosome s ○ How does cell division affect number “2n” the number of chromosomes in Gametes chromosome daughter cells? Somatic cells only only number reproduce by mitosis Formed by All somatic A type of cell meiosis cells division that Reproduce results in two genetically only by identical Mitosis diploid No gametes daughter cells. Meiosis A type of cell division that  🧬 ⌈ L6 ⌋ Cell Cycle and Control Points Synthesis of DNA, chromosomes are duplicated Duplication of centrosome G2 (Second Gap) the cell grows more, makes proteins CELL CYCLE and organelles ➔ The cell cycle is a series of events a cell reorganize its contents in preparation goes through as it grows and divides for mitosis into two daughter cells. It is a highly regulated and coordinated process G0 (Resting State) that ensures the accurate duplication and distribution of genetic material “inactive” state (DNA) to new cells. ○ they are not dividing or preparing to divide performing other cellular duties Reversible and non-reversible (CELL CYCLE) CONTROL POINTS The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock. The cell cycle control system is regulated by both internal and external controls. The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received. This regulation makes sure that cells don't divide under unfavorable conditions (for instance, when their DNA is damaged, or when there isn't room for more cells in a tissue or organ). MITOTIC PHASE (M PHASE) Mitosis and cytokinesis. INTERPHASE Is the period of cell growth when the cell synthesizes new molecules and organelles. G1 (First Gap) first gap phase the cell grows physically larger, copies organelles S Phase (Synthesis Phase) Synthesis phase G1 Checkpoint  The main decision point of a cell. If a cell receives a go-ahead signal at DNA Was the DNA completely the G1 checkpoint, it will usually Replication copied during the S phase? complete the S, G2, and M phases and divide. If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state 📝 If errors or damage are detected, the cell called the G0 phase. will pause at the G2 checkpoint to allow for repairs. If the checkpoint mechanisms detect CHECKLIST problems with the DNA, the cell cycle is halted, and the cell attempts to either Size Is the cell large enough to complete DNA replication or repair the divide? damaged DNA.. Nutrients Does the cell have enough energy reserves or available nutrients to divide? 📝 If the damage is irreparable, the cell may undergo apoptosis or programmed cell death. This self-destruction mechanism Molecular Is the cell receiving positive ensures that damaged DNA is not passed Signals cues (such as growth factors) onto daughter cells and is important in from neighbors? preventing cancer. DNA Is any of the DNA damaged? Integrity M Phase Checkpoint Also called, spindle checkpoint. Cells will not begin anaphase until all chromosomes are properly attached to the spindle at the metaphase plate. This mechanism ensures that daughter cells have the correct number of chromosomes. CHECKLIST Are the sister chromatids correctly attached to the spindle fibers? 📝 If a cell doesn’t get the go-ahead cues it needs at the G1, end subscript checkpoint, it may leave the cell cycle and enter a resting state called G0. Some cells stay permanently in G0, while others resume dividing if conditions improve. G2 Checkpoint Additional checkpoint before M phase. CHECKLIST 📝 the cell examines whether all the sister chromatids are correctly attached to the DNA Is any of the DNA damaged? spindle fibers. Because the separation of the Integrity sister chromatids during anaphase is an irreversible step, the cycle will not proceed until all the chromosomes are firmly attached to at least two spindle fibers from opposite poles of the cell. 📝 The cell looks for "straggler" chromosomes that are in the wrong place (e.g., floating around in the cytoplasm). If a chromosome is misplaced, the cell will pause mitosis, allowing time for the spindle to capture the stray chromosome. (CELL CYCLE) REGULATORY PROTEINS Play a crucial role in controlling the progression of the cell cycle, ensuring that each phase occurs in the right order and that the cell only advances EXTERNAL FACTORS THAT AFFECT CELL CYCLE when conditions are favorable Growth factors are released by certain TWO TYPES OF REGULATORY PROTEINS ARE cells and stimulate other cells to divide. INVOLVED IN CELL CYCLE CONTROL Cyclins EXAMPLE Platelet-derived growth factor Cyclin-dependent Kinases (Cdks) (PDGF) - is made by blood cell fragments called platelets The activity of a Cdk rises and falls with Anchorage dependence — to divide, changes in the concentration of its they must be attached to a cyclin partner substratum MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a In density-dependent inhibition, cell’s passage past the G2 checkpoint crowded cells will stop dividing into the M phase ○ MPF promotes mitosis by phosphorylating a variety of proteins. ○ MPF stimulates fragmentation of the nuclear envelope by phosphorylation of various proteins of the nuclear lamina during the prometaphase of mitosis. ○ MPF also contributes to the molecular events required for chromosome condensation and spindle formation during prophase. Once the cyclin-CDK complex has 🧬 L7 ⌋ Cancer Cells performed its function, it is targeted for destruction and degradation. ⌈  The number of cells in a tissue is determined by CANCER CELLS the balance between CELL DIVISION and CELL Cancer cells do not respond normally DEATH. to the body’s control mechanisms. Uncontrollable CELL DIVISION leads to formation Cancer cells do not need growth of abnormal growth called TUMORS. factors to grow and divide: ○ Tumors can be Benign or Malignant. ○ They may make their own ○ Benign Tumors are slow-growing growth factor and constrained by surrounding ○ They may convey a growth connective tissue so they do not factor’s signal without the spread to other organs. They can still presence of the growth factor be harmful or even kill by pressing on ○ They may have an abnormal nearby nerves, blood vessels, or brain cell cycle control system tissue. Cells that acquire the ability to divide EXAMPLES indefinitely are undergoing Pituitary Tumors transformation. Cancer cells that are which may press not eliminated by the immune system on optic nerves form tumors, masses of abnormal cells and cause loss within otherwise normal tissue. of vision. ○ Cancers are Malignant Tumors. This Benign Tumor tumor can spread beyond the limit of the original organ where it comes If abnormal cells remain only at the from and to other organs of the body. original site, the lump is called a benign tumor. Malignant Tumor Cancer starts from damage in the DNA of a cell. Malignant tumors invade surrounding This DNA damage is called MUTATION. tissues and can undergo metastasis, ○ Mutations happen when the cell the spread of cancer cells to other duplicates its DNA prior to cell parts of the body, where they may form division and makes mistakes. additional tumors ○ These damages are usually detected and repaired BEFORE the cell can Localized tumors may be treated with divide, but sometimes some of them high-energy radiation, which damages may be ignored and transferred to the DNA in the cancer cells daughter cells. To treat metastatic cancers, ○ If the mutation is located in one of chemotherapies that target the cell many genes that control the cell cycle may be used cycle, it may affect the regulation of the cell cycle in the cell carrying it, and make the cell divide faster than it’s supposed to. ○ Usually, one mutation is not enough to cause cancer, but as it makes the cell cycle control LESS reliable, many more DNA damages, or mutations, would go unnoticed. ○ Cancer is usually the result of accumulation of MANY mutations of genes involved in cell cycle control and DNA repair. ○ This commonly happens over a long period of time, over many rounds of cell divisions, and this explains why cancers are common in older people. ○ Some people are said to be VIDEO TRANSCRIPT PREDISPOSED to cancer. This is Cancer, How Cancer Starts, How Cancer Spreads, Where and Why? because they are born with a mutation that makes them more  likely to develop a certain type of cancer. This mutation alone is not enough to cause cancer but it starts the process of making the cells cancerous. ○ The person carrying it is one step further down the road towards developing cancer than others who do not have the mutation. ○ Cancer cells do not stick together like normal cells, they move and invade nearby tissues and organs. This is a local spread. ○ They may also spread to further away organs by means of blood or lymph circulation. This is a systemic spread. ○ Metastasis is the spreading of cancers to non-adjacent organs. ○ Cancer cells from the original tumor, or primary cancer, can break out and maybe be taken up by a blood or lymph vessel for a ride throughout the body. ○ They can then squeeze out from the vessel into other tissues and start a new tumor growth in the new location which will become secondary cancer. ○ While travelling in the bloodstream, a cancer cell usually stops at the first place where the vessel is getting so narrow that it gets stuck. ○ As blood flow from most organs goes to the capillaries of the lungs, this is where cancers spread the most. ○ Lungs are indeed the most common site of secondary cancers. ○ Likewise, while travelling in the lymphatic system, cancer cells commonly get stuck in the nearest lymph nodes, where the vessels get narrower. This is the reason why surgeons usually remove nearby lymph nodes when removing tumors.