Chapter 6 THE CELL CYCLE

Figure 9.01 그림 6.1 세포분열과 예정세포사는 발생을 조절함

A. The Cell Cycle Events that occur in the life of a cell. Includes 3 major stages: Interphase ( 간기 ) Karyokinesis (mitosis: 유사분열 ) Cytokinesis ( 세포질 분열 )

1. Interphase Cell is not dividing. G 1 Phase - carries out basic functions & performs specialized activities. duration is extremely variable contains restriction checkpoint ( 검문지점 )~ cell “decides” to: - divide - enter a quiescent phase (G 0 ) - die

G 0 Phase – a cell can exit the cycle at G1 to enter this phase The cell maintains specialized characteristics, but does not divide. Ex. neurons & muscle cells S Phase - cell replicates chromosomes & synthesizes proteins. [animal cells replicate centrioles as well]

G 2 Phase - cell synthesizes additional proteins (ex. tubulin) & assembles/stores membrane material.

2. Karyokinesis (mitosis; M phase) Equal distribution of replicated genetic material (chromosomes). Each replicated chromosome now consists of two identical copies (chromatids). Chromatids are attached to each other at the centromere.

Prophase replicated chromosomes condense centrosomes separate & migrate toward opposite sides of cell mitotic spindle forms (microtubules grow out from centrosomes) nucleolus disappears

Prometaphase nuclear membrane breaks down spindle fibers attach to centromeres of chromosomes

Metaphase chromosomes are lined up single-file along equator of mitotic spindle.

Anaphase centromeres part, sister chromatids (now called chromosomes) separate chromosomes move toward opposite poles

Telophase mitotic spindle breaks down chromosomes decondense nuclear membranes reform around two nuclei nucleoli reappear

3. Cytokinesis Distribution of cytoplasm to daughter cells. begins during anaphase or telophase depending on the cell type differs in animal & plant cells

Cytokinesis in animal cells: cleavage furrow ( 난할구 :slight indentation) forms around equator of cell. actin & myosin microfilaments act like a drawstring to pinch the cell in two. usually an equal division.

Cytokinesis in animal cells

Cytokinesis in plant cells: phragmoplast ( 격막형성체 : microtubule structure) forms in cytoplasm & traps vesicles containing cell wall material. vesicles fuse, forming a cell plate across midline of cell. cell plate gives rise to two primary cell walls.

Does cytokinesis always accompany karyokinesis? Karyokinesis in the absence of cytokinesis results in a syncytium (mass of multinucleated cells).

Control of the Cell Cycle Checkpoints - groups of interacting proteins that ensure cell cycle events occur in the correct sequence. ( 세포분열을 할 것인지, 손상된 DNA 복구를 위해 분열을 정지할지, 휴지상태로 진입할지, 죽어야 할 것인지 결정함 ) 튜불린 합성 유전물질, 단백질합성 세포막 생성에 필요한 물질 합성

Shortening of telomeres - loss of telomere DNA signals cell to stop dividing. Some cells produce telomerase (enzyme that continually adds telomere DNA).

지체 (Lag) 가닥 DNA 의 말단 문제 해결 선도가닥 지체가닥 주형가닥을 복제할 때 Primer ( 시발자, 개시자 ) 가 필요함 시발자

Function of telomerase

Contact Inhibition - healthy cells stop dividing when they come in contact with other cells.

Hormones - stimulate cell division. Ex. Estrogen stimulates uterine( 자궁내막 ) cell division Growth factors - proteins that stimulate local cell division. Ex. Epidermal growth factor (EGF) stimulates epithelial cell division filling in new skin underneath a scab Interaction of kinases & cyclins - activate genes that stimulate cell division. 그림 6.13 사이클린은 세포주기를 조절한다.

Stem Cells Cells used to replenish tissues When a stem cell divides, one daughter cell will specialize and the other daughter cell will remain a stem cell Ex: basal layer of skin, bone marrow, & small intestine

B. Apoptosis Programmed cell death; part of normal development. Eliminates excess cells and cells that could grow uncontrollably. 그림 발생중인 닭은 다방면의 예정세포사로 발가락을 만드나 오리는 그렇지 않아 물 갈퀴막을 계속 유지

Steps of Apoptosis:

C. Cancer (loss of cell cycle control) Condition resulting from excess cell division or deficient apoptosis. Characteristics of Cancer Cells: can divide uncontrollably & eternally dedifferentiation are invasive are heritable & transplantable lack contact inhibition readily metastasize exhibit angiogenesis exhibit genetic mutability

Causes of Cancer: Over-expression of oncogenes Oncogenes are genes that trigger limited cell division. Inactivation of tumor suppressor genes Tumor suppressor genes prevent a cell from dividing or promote apoptosis.

Normal functioning of oncogenes & tumor suppressor genes may be affected by environmental factors: carcinogens radiation viruses diet exercise habits