本期內(nèi)容是有絲分裂的基礎(chǔ)理論部分，實(shí)驗(yàn)手冊(cè)與實(shí)驗(yàn)?zāi)M請(qǐng)看后兩期。本部分內(nèi)容來自 University of California, Berkeley - UC Berkeley Extension, 虛擬實(shí)驗(yàn)的內(nèi)容來自 Labster. 本部分內(nèi)容均不會(huì)標(biāo)記為為原創(chuàng)，但由于是UP主購買的課程，因此不接受非授權(quán)的轉(zhuǎn)載，謝謝您的理解。

每一個(gè)生物基礎(chǔ)實(shí)驗(yàn)均會(huì)分為三部分：第一部分為實(shí)驗(yàn)的生物理論；第二部分為實(shí)驗(yàn)的指導(dǎo)手冊(cè)；第三部分為 Labster 的虛擬實(shí)驗(yàn)?zāi)M。第一部分的基本信息由 Ying Liu, Ph.D. 提供，第二部分的實(shí)驗(yàn)手冊(cè)來自 Labster, 第三部分的實(shí)驗(yàn)?zāi)M過程由UP主操作。

L6 - Mitosis

Why Do Cells Divide?

- Unicellular organisMs divide to reproduce;

- Multicellular organisMs divide to allow:

????Development from a fertilized egg;

????Growth;

????Repair.

Cell Cycle

The sequence of events that a cell goes through from its origin (birth) to its own division into two daughter cells is called the cell cycle.

Interphase

- Interphase: the period between cell divisions;

- Interphase is divided into G1 (gap 1), S phase, and G2 (gap 2);

- A cell grows in size during G1 and G2 (organelles and ribosome numbers increase, new proteins synthesized).

Interphase accounts for most of the time in a cell cycle;

For a cell that divides every 24 hours, >20 hours are spent in interphase;

DNA synthesis (replication) happens in S phase.

Duration of Cell Cycle

Cell Division

- Mitosis: division of the nucleus;

- Mitosis is divided into prophase, metaphase, anaphase and telophase;

- Cytokinesis: division of the cytoplasM.

Control of Cell Cycle

- Checkpoints: can delay the cell cycle until certain conditions are met;

- There are 3 major checkpoints;

- G1/S: check for DNA damage; if passed, the cell is committed to divide.

- If DNA damage is detected:

????DNA repair mechanisM;

????Apoptosis: programmed cell death.

- G2/M: verifies if DNA replication is complete

- Metaphase: verifies spindle assembly and chromosome attachment

Chromatin and Chromosome

- Interphase DNA is organized into loose structures called chromatin; during mitosis, chromatin condenses to form chromosomes;

- After DNA replication, the two copies stay attached at a region called the centromere, each copy is called a chromatid.

Chromosomes

- Replication origin: multiple, origin of DNA replication, spread bi-directionally;

- Centromere: site for mitotic spindle attachment, also holds the duplicated chromosome together before cell division;

- Telomeres: special caps on each end; help in the replication of chromosome ends; also help protect chromosome ends.

Chromatin and Chromosome

Chromosomes

- Every species has characteristic numbers;

- Karyotype.

Karyotyping

- Collect tissue sample (WBCs) and culture;

- Add chemical to stimulate mitosis;

- Add chemical to stop mitosis in metaphase;

- Stain sample, take photo and arrange chromosomes.

Ploidy

- Ploidy refers to the number?of ‘sets’ of genetic material;

- Humans are diploids;

- Xenopus (frogs) are tetraploids.

Mitotic Spindle and Centrioles

- Mitotic spindle and centrioles are made of microtubules;

- Both are involved in chromosome segregation.

Duplication of Centrioles

- Centrosome (and centrioles) is also duplicated in S phase;

- In animal cells, centrosomes are microtubule organizing centers;

- Plant cells do not have centrosomes.

Phases

Mitosis in Animal vs. Plant Cells

Cell Cycle Control System

- Progression through the cell cycle depends on cyclin-dependent protein kinases (Cdks);

- Cdks are regulated by cyclins, whose concentrations vary in a cyclical fashion during cell cycle;

- Once activated, cyclin-Cdk complex phosphorylates key proteins to initiate particular steps in cell cycle.

Oncogenes

- Proto-oncogenes: normal genes that promote cell cycle; when mutated, become oncogenes;

- Oncogenes act in a dominant manner: a gain-of-function mutations in a single copy of the proto-oncogene can drive a cell toward cancer;

- Examples of proto-oncogenes include: Ras, ERK (MAP Kinase), EGF receptor, and transcription factor myc.

Tumor Suppressors

- Tumor suppressors: genes that suppress tumor formation; negative regulators of cell cycle;

- Mutations in the p53 gene (involved in DNA damage repair) are found in about half of all human cancers.

- Loss-of-function mutations in tumor suppressor genes act in a recessive manner: the function of both copies of the gene must be lost to drive a cell toward cancer;

- Examples of tumor suppressors include Rb, p53 and p27.

Genetic Basis for Cancer

- Proto-oncogenes (gas pedal): products promote the cell cycle and prevent cell death (apoptosis);

- Tumor suppressor genes (brake): products inhibit the cell cycle and promote apoptosis.

Cancer: Accumulation of Mutations

- Cancer: a group of > 100 diseases that start with uncontrolled cell division;

- Usually takes a few mutations to form benign tumors, and then malignant tumors after metastasis.

Cancer Drug

- Paclitaxel: a compound extracted from yew tree;

- Prevents microtubule depolymerization, inhibits mitosis;

- Used in chemotherapy for treating cancers.

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