Understanding Mitosis and Meiosis: Key Concepts Explained

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Oakland Community College**We aren't endorsed by this school

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BIO 1511

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Biology

Date

Dec 11, 2024

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Chapter 11- Cells of all multicelled eukaryotes reproduce by mitosis and cytoplasmic division.- Zygote (Fertilized egg) –(cell division)—Embryonic Stem Cells (5-7 days): All identical, All have the potential to become any cell type.–(cell division)Embryo (배아)- Frozen embryos at this stage will never develop into baby unless implanted in uterus 자궁이식What is the difference between asexual and sexual reproduction?“Reproduction” has many meanings: 1. Cellular reproduction : cell division = Mitosis & Meiosis2. Birth of new organisms (Chapter 38)(1) Asexual reproduction: one parent produces genetically identical offspring - Mitosis무성생식 (부모와 자식이 유전적으로 똑같음, 자신을 복제해서 똑같이 자손을 만드는..)(2) Sexual reproduction: 2 genetically different parental sex cells fuse to create a new offspring유성생식 (난자+정자, 두개의 다른 부모 유전자가 융합하여 자손을 만드는..)Define: MITOSIS 유사분열1) nuclear division 2) results in 2 nuclei (핵) that are genetically identical to the parent cell 3) Followed by Cytokinesis (division of the cytoplasm) 세포질분열이 뒤따른다.4) Produces 2 separate cells5) Maintains the chromosome number in the new cells (2N 2N)6) Used for : Growth & Repair of tissuses (multicellular organisms)Asexual reproduction (some unicellular organisms, ex. Amoeba, starfish)Define: MEIOSIS 감수분열1) nuclear division of a diploid (2N) cell 2) results in 4 haploid (1N) genetically different nuclei3) The process of cytokinesis 4) Produces separates the nuclei into 4 separate daughter cells5) Reduces the chromosome number by ½ (reduction division) (2N 1N)6) Used for : production of gametes (egg & sperm cell)* At the beginning of cell division;- DNA must be condensed 응축하다 into chromosomes (X-shaped structure) Tight condensation keeps the chromosomes from getting tangled and breaking as they move aroundduring the nuclear division process. 긴밀한 응축은 염색체가 핵분열 과정에서 이동할 때 엉키거나 부서짐 방지* Before cell division;DNA in the nucleus must be replicated* How many feet of DNA are in a nucleus?About 6Ft

Chromosome StructureReview telomeres and the significance of stem cells- Every time a cell divides, the chromosomes shorten by about 100 nucleotides at their ends- TELOMERES : To protect against the loss of genetic material, chromosomes are capped.Noncoding DNA sequences (repeats of TTAGGG)found at the ends of chromosomes.Each time a cell divides the telomeres shorten When the telomeres are too short, cell division stopsStem cells줄기세포 only make telomerase—an enzyme that lengthens telomeres by addingTTAGGGrepeats to them Rebuilds the telomeresHaploid VS Diploid Cells1) Haploid (1N) : Cell with only one set of chromosomes (one gene for each trait) are haploid.- Symbolized by N- All gametes (sex cells) are haploid- haploid cells are the result of meiosis2) Diploid (2N) : Cells having homologous chromosomes (two genes for each trait) are diploid.- Symbolized by 2N- All somatic cells (body cells) are diploid- Diploid cells are created through mitosis* Our body cells are diploid. One from mom and one from dad.Review the steps of the cell cycle. Describe what happens during the parts of Interphase. * Interphase + Mitosis (Prophase+Metaphase+Anaphase+Telophase) + Cytokinesis1) Interphase= G1 + S + G2- A typical body cell spends most of its life in interphase (90%)- cell increases its mass, roughly doubles the number of its cytoplasmic components, and copies its chromosomes in preparation for division.- Nucleus & Nucleolus are visible (Some cells have more than one nucleolus)- G1 = Metabolic business & growth- S = DNA synthesis (also known as DNA replication)DNA resembles a tangled mass (unwound DNA) chromatin- G2 = Some growth & prep for cell division2 Centrosomes appear together at one end of the cell- Centrosomes contain a pair of centrioles. - Centrioles release microtubule fibers that become the mitotic spindle.- Microtubules are protein fibers that help move chromosomes around.- M = Mitosis (or meiosis)

2) Prophase= Beginning of Mitosis- DNA begins to condense (wind up) into chromosomes (Visible Chromosomesinside the cell under a light microscope)- Centrosomes separate and move to opposite ends of the cell (crossing over)- Microtubules are released and spindle formation occurs - Nuclear membrane breaks down & disappears- Spindlemicrotubules attachto chromosomes- Chromosomes are visible in the nucleus (early)- Chromosomes appear scattered, no nucleus (late)3) Metaphase- Spindle microtubules shorten & lengthen to pull the chromosomes into position- Chromosomes line up in the middleof the cell (checkpoint)4) Anaphase- Spindle microtubules at each end of the cell pull- Sister chromatids separate & move to opposite ends of the cell5) Telophase- (once chromatids separate they are called chromosomes)- Chromosomes reach opposite ends of the cell- Spindle microtubules break down- Chromosomes unwind- New nuclear membranes reform- TWO nuclei are visible inside ONE cell6) Cytokinesis분열 = division of the cytoplasm“Like a drawstring tightening- New membrane that forms from the fusion of these vesicles will partition the two new cells at the end of division.How does cytokinesis difference in animal and plants cells?- In animal cell: animal cells have a mesh of cytoskeletal elements under the plasma membranecalled the cellCortex. The cell cortex reorganizes during anaphaseto form a band of microfilamentsand motor proteinsthat wraps around the cell. The band is called a contractile수축성 ringbecause it contracts after telophase, pulling the membrane inwardas it does. The sinkingplasma membrane becomes visible on the outside of the cell asan indentation called a cleavagefurrow (분열 고랑). - In plant cell: by contrast, have a stiff cell wallaround their plasma membrane. Before mitosis, aring ofparallel 팽팽한 microtubules formsaround the future plane of division. These microtubules reorganize during mitosisto form the spindle, and by late anaphasehave guided vesicles tothe plane of division.During telophase, the vesicles start to fuse into a flat cell plate. Themembranes

of the merged vesicles will become the plasma membranes separating the twodescendant cells, and the vesicles’ contents will be converted to walls.Do all cells divide at the same rate? No. - Not all cells divide at the same rate. For example, neurons are a specialized type of cell in the nervoussystem, and they divide very rarely. By contrast, skin cells divide frequently in order to repair injuries or toreplace old skin cells that have died.There are several checkpoints (√ ) in the cell cycle. Why are cell cycle checkpoints important?- Checkpoints stop the cell cycle and analyze the DNA for errors (& usually fixes the errors) before thecycle can Continue. (체크 표시마다 DNA를 체크하고 error가 있을 때 Fix할수 있음)- Builtin checkpoints ensure that the cell’s DNA has been copied completely, that it is not damaged, andeventhat enough nutrients are available to support divisionPathological Mitosis- When cell checkpoints(P53) fail (due to mutation), a cell loses control over the cell cycle- DNA damage is not corrected- Interphase may be skipped and the cell divides over & over- Producing a collection of abnormal, mutated, dysfunctional cells = TUMOR 종양 (neoplasm)What does a properly functioning p53 gene do?- Normal P53 : When cellular damage occurs. _53 arrests the cell cycle until the damage is repaired. Ifdamage cannot be repaired, apoptosis occurs.* DNA damage Cell cycle abnormalities Hypoxia –(P53)Cell cycle arrest DNA repair Cell cyclerestartIf fail to repair, Apoptosis (Programmed cell death)- Mutated P53 : Mutated P53 des not arrest the cell cycle. The damaged cell continues to divide, result incancer.* DNA damage Cell cycle abnormalities Hypoxia –(mutated P53)Cell cycle continues Cells can become cancerous.- Cancer (Carcinomas)• From the Latin word “Crab” • Cancer is a genetic disease• Cells become cancerous due to mutations. • 2 types of mutations• Inherited (direct cause of a small number of cancers) • Acquired (more common cause of cancer)• Environmental causes: cigarette smoke, radiation, hormones, dietReview tumors: benign vs malignant (and the concept of metastasis)- Tumor is new growth, uncontrolled by mitosis. - Benign 양성 tumors 종양 tend to be encapsulated 캡슐화.Benign neoplasms such as warts 사마귀 are not inherently 본질적으로 dangerous. They grow very slowly,and their cells retain the plasma membrane adhesion proteins that keep them properly anchored in their home

tissue. - A malignant neoplasm gets progressively worse, and is dangerous to health. - Malignant cells typically display the following three characteristics:1) First, like cells of all neoplasms, malignant cells grow and divide abnormally.2) Second, the cytoplasm and plasma membrane of malignant cells are altered. Both are indications ofcellularmalfunction. 세포 오작동3) these cells do not stay anchored properly in tissues because their plasma membrane adhesionproteins are defective or missing. Malignant cells can slip easily into and out of vessels of the circulatory andlymphatic systems. The process in which malignant cells break loose from their home tissue and invade otherparts of the body is called metastasis.- Malignant 악성 tumors are cancerous 암. (악성종양이 캡슐을 터뜨림.) Cancer growth and spread. - Metastasis 전이= spread of diseaseReview apoptosis vs necrosis- Cell Death의 2가지 방법- Apoptosis= Programmed cell death (Die) membrane blebbing (막 출혈) The cell break apart intoseveral apoptotic bodies, which are then phagocytosed 식세포화. NO inflammation (염증)- Necrosis= Damaged, trauma cell death by injury. Cell swelling plasma membrane rupture 파열.Cellular andnuclear lysis causes inflammation.What are HeLa cells? 불멸의 세포- Henrietta Lacks 환자 이름에서 따옴. 성과 이름 2글자씩- It is Immortal cells. Taken from a cancerous tumor. Cells divide again and again… Telomeres rebuild Easy to culture 배양, Precious to scientific research 과학연구에 귀중함- The Geys(과학자) discovered how to grow poliovirus in HeLa cells, a practice that enabled them todetermine whichstrains of the virus cause polio. That work was a critical step in the development of polio vaccines, whichhave since saved millions of lives.Chapter 12- DNA variation is almost always advantageous, because genetically diverse populations are more resilient적응하다 to environmental change. - Genetically different offspring create a diverse population.- A diverse population has a better chance of surviving environmental change than clones 복제.- Asexual reproductionproduces genetically identical individuals low genetic diversity.- Sexual reproductionproduces offspring genetically different from one another and from the parentsbecause it

processes mix genetic information from two parents who differ in the details of their DNA,Organisms that use sexualreproductionproduce genetically different offspring.What are homologous chromosomes?- In a nucleus, pair of chromosomes that have the same length, shape, centromere location, and thesame genes.- the two homologous chromosomes of a pair are similar but notidentical. Matenal vs paternal (They may differ slightly)- They are inherited from two parents that differ genetically, so their DNA sequence differs slightly.- Sister chromatids attach at the centromere and form one X-shaped chromosome: homologous랑 다름- Gametes have a single set of chromosomes, so they are haploid (n)- Meiosis : a nuclear division mechanism that halves the chromosome number, is a necessary part ofgamete formation and sexual reproduction. meiosis also gives rise to new combinations of parental alleles.- Meiosis in diploid germ cells gives rise to eggs (female gametes) or sperm (male gametes).- germ cells : 생식세포 (male : inside testes 고환, female : ovaries 난소, plant일 경우 정자 : anther)Meiosis 1* Homologous chromosomes separate into 2 nucleiMeiosis 2* Sister chromatids separate into 4 nuclei- After meiosis I, the chromosomes are still duplicated (sister chromatids remain attached). During meiosisII, the sisterchromatids are pulled apart, and each becomes an individual, unduplicated chromosome. Thechromosomes are sorted into four new nuclei. Each new nucleus has one copy of each chromosome, so it is haploid (n).- In summary, meiosis partitions the duplicated chromosomes of one diploid nucleus (2n) into four haploid(n) nuclei.- A zygote is the first cell of a new individual. meiosis halves the chromosome number, and fertilizationrestores it.What is happening in meiosis I? Homologous chromosomes separate into 2 nuclei- DNA replication occurs before meiosis I, so each chromosome starts out with sister chromatids.

( Meiosis began with 2 cell that had 2 chromosomes)- Early in prophase I of meiosis, all chromosomes in the cell condense. (Crossing over 발생)1) Prophase I : crossing over- The chromosomes condense, and homologous chromosomes align tightly and swap segments - The nuclear envelope breaks up. - A spindle forms, and by the end of prophase I, microtubules attach one chromosome of eachhomologous pair to one spindle pole, and the other to the opposite spindle pole. - These microtubules grow and shrink, pushing and pulling the chromosomes as they do.2) Metaphase I (여기로 넘어오면서 Independent Assortment 발생)- All of the microtubules are the same length, and the chromosomes are aligned midway between the spindle poles.3) Anaphase I- Microtubules of the spindle move the homologous chromosomes of each pair away from one anotherand toward opposite spindle poles. 4) Telophase I- Two sets of chromosomes reach the spindle poles- A new nuclear envelope forms around each set as the DNA loosens u. - The two new nuclei are haploid (n); each contains one complete set of chromosomes. - Each chromosome is still duplicated (it consists of two sister chromatids). - The cytoplasm often divides at this point.5) Cytokinesis I- One (2N) nuclei Four (1N) nuclei- and ended with 4 cells that possess one chromosome eachWhat is happening in meiosis II?- Meiosis II proceeds simultaneously in both nuclei that formed in meiosis I. 1) Prophase II- The chromosomes condense and the nuclear envelope breaks up- A new spindle forms. By the end of prophase II, spindle microtubules attach each chromatid to onespindle pole, - And its sister chromatid to the opposite spindle pole. 2) metaphase II- These microtubules push and pull the chromosomes, aligning them in the middle of the cell3) Anaphase II- the spindle microtubules move the sister chromatids apart and toward opposite spindle poles.- Each chromosome is now unduplicated(it consists of one molecule of DNA).4) Telophase II- The chromosomes reach the spindle poles. - New nuclear envelopes form around the four clusters of chromosomes as the DNA loosens up. - Each of the four nuclei that form are haploid (n), with one set of (unduplicated) chromosomes. - The cytoplasm often divides at this point.5) Cytokinesis IIWhat 2 processes contribute to the genetic variation seen in daughter cells that completedmeiosis?1) Crossing over(Prophase 1)- Chromosome and its homologous partner exchange corresponding pieces of DNA during meiosis- Swapping segments of DNA shuffles alleles between homologous chromosomes. It breaks up thecombinationsof alleles that occurred on the parental chromosomes, and makes new ones on the chromosomes that

end up in gametes. Thus, crossing over introduces novel combinations of alleles among offspring.- Genetic code가 swab position 하기 때문에 서로 다른 4개의 chromatids가 생성- In humans, 46-95 crossovers occur per meiosis. On average, each chromosome has at least onecrossover event.2) Independent Assortment (Meiosis 1; Prophase 1 Metaphase 1)- Chromosome segregation- Assortment of chromosomes into daughter cells is random.- How to do lined up? RANDOM.- Normally, all of the new nuclei that form in meiosis I receive a complete set of chromosomes. However,whether a new nucleus ends up with the maternal or paternal version of a chromosome is entirely random.- The process of chromosome segregation 분리 begins in prophase I (microtubules에 부착)- Long ago, the molecular machinery of mitosis became remodeled into meiosis. Mitosis와 Meiosis 2 유사.+ 여기에도 체크포인트 역할을 하는 분자가 molecule 있음 (DNA검사 및 복구)- The shared molecules and mechanisms imply a shared evolutionary history.- sexual reproduction probably originated with mutations that affected processes of mitosisWhat is nondisjunction? 비분열 - Failure of chromosomes to separate properly during nuclear division. (meiotic cell division)(50 : 50 으로 분열해야하는데 60 : 40 으로 잘못 분열되는 것)- This alters the number of chromosome in the gametes- Heritable 유전적 Changes in Chromosome NumberWhat happens during sexual reproduction?- Female and male have 46 chromosomes- Through meiosis, Egg and sperm cell have 23 chromosomes- Through Sexual reproduction, Fertilization restores the chromosome number in the new offspring. (46 Chromosomes) - Mitosis 후 배아 (46 Chromosomes)

Why are gametes made by meiosis instead of mitosis?- the numbers of chromosomes are reduced to half during meiosis and then the normal diploid numbers ofchromosomes are regained during the process of fertilization.Turner : X 하나만 있음. XO = 미성숙한 몸.XXX 증후군 : X 3개인 여자. 일반적으로 이상이 없지만 경미한 정신장애클라인펠터 증후군 : 남성인데 XX 두개이상 가지는 것 ex) XXXY) 키가 큼. 나이가 들수록 여성화? XYY 증후군: 가벼운 정신장애. 키가 큼. 범죄에 취약한것으로 여겨졌으나 아닌것으로 반증.