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Flashcards in Life Cycle of the cell Deck (21):

In multicellular animals, cells are divided into what two broad categories based on the way in which they divide?

Reproductive cells and Somatic cells


Where are reproductive cells found?

ovaries, testicles and give rise to eggs and sperm


What process does the reproductive cells use to divide?



What are somatic cells?

all of the cells in the body except the reproductive cells


With what process do somatic cells divide?



The life cycle has been divided into what two major periods?

interphase - when the cell is growing, maturing, and differentiating and
mitotic phase - when the cell is actively dividing


What is interphase?

the period between cell divisions (carries out normal life-sustaining activities
- the nucleus and nucleoli are visible
- the chromatin is arranged loosely throughout the nucleus
- centrioles can be seen in various states of replication


What are the three subphases of interphase?

growth one, synthetic, and growth two - cell growth occurs throughout all of them - these phases flow as a smooth continuous process


The first part of interphase is called?

growth one


How long can the interphase subphase - growth one last?

from a few minutes, to several weeks or even years


How is G1 is defined?

by intensive metabolic activity and cellular growth
- the cell doubles in size and the number or organelles also doubles
- centrioles begin to replicate in preparation for cell division


The sythetic (S) phase is marked by?

DNA replication - histones are formed and assembled into chromatin forming new identical replicas of the genetic material


What is the growth two (G2) phase?

it is very brief and includes the synthesis of enzymes and proteins necessary for cell division and continued growth of the cell
- centrioles complete their replication at the end of the G2 phase


What happens during prophase of the mitotic phase?

1. Prophase: Chromatin coils and condenses to form barlike chromosomes that are visible with light microscopy. These chromosomes are composed of two identical chromatids linked together at a constriction in their middle known as the centromere or kinetochore. The cytoplasm becomes more viscous as microtubules from the cytoskeleton are disassembled and the cell becomes round. Two pairs of centrioles form anchors on which new microtubules are constructed, and as the microtubules lengthen, they push the centrioles farther and farther apart. In this way a mitotic spindle is formed that provides the structure and machinery necessary to separate the chromosomes. Because transcription and protein synthesis cannot occur while the DNA is tightly coiled, the appearance of chromosomes marks the cessation of normal synthetic processes. Prophase is thought to conclude with the disintegration of the nuclear envelope.


What are the 4 stages of the mitotic phase?

Prophase, metaphase, anaphase, and telophase


What happens during metaphase?

2. Metaphase: Chromosomes line up in the exact center of the spindle, known as the equator. The chromosomes are evenly spread apart and form what is called the metaphase plate midway between the poles of the cell. The centromere of each chromosome is attached to a single spindle fiber.


What happens during anaphase?

Anaphase: The centromeres of the chromosomes split apart and each chromatid becomes its own chromosome. The spindle fiber separates, each spindle segment shortens, and the twin chromosomes are pulled away from each another. The chromosomes take on a V shape as they are dragged at their midpoint toward the centrioles at opposite ends of the cell. The cell becomes elongated, and the cytoplasm begins to constrict along the plane of the metaphase plate. Although anaphase is the shortest phase of mitosis and usually lasts only a few minutes, its importance is clear in light of the devastating consequences if an error were to occur in chromosome separation. In anaphase the advantage of separating compact bodies of chromosomes, rather than long thin threads of chromatin, is particularly obvious.


What happens during telepase?

Telophase: Begins when chromosomal movement stops. The chromosomes, having reached the poles, begin to unravel, elongate, and return to a diffuse threadlike form (chromatin). A nuclear envelope appears around each new set of chromosomes, and nucleoli appear in each nucleus. The microtubules that made up the spindle in the earlier phases of mitosis disassemble, and a ring of peripheral microfilaments begins to squeeze the cell into two parts. Ultimately, the cell pinches itself in half, dividing the cytoplasm and forming two completely separate daughter cells. The process of cytoplasmic division is called cytokinesis and marks the end of telophase.


Why is it important for chromatin to coil and form discrete chromosomes before cell division?

Transcription and protein synthesis cannot occur while the DNA is tightly coiled.


What three factors play a role in the control of cell division?

Normal cells stop dividing when they come into contact with surrounding cells. This phenomenon is called contact inhibition. 2. Growth-inhibiting substances may be released from cells when their numbers reach a certain point. 3. A number of checkpoints are reached during cell division when the cell reassesses the division process. These checkpoints occur during the G1 and G2 phases of interphase.


What is the genetic basis of cellular differentiation?

The position of genes in chromosomes determines the genetic basis of cellular differentiation. Some genes may be located on a region of the chromosome that is available for transcription, whereas other genes may be located inside the molecule and cannot be reached by transcription molecules. We say that one gene is “turned on” while the other gene is “turned off.” Genes can be turned off permanently or temporarily. Chromosomes are dynamic in their ability to twist, so that a gene that was once inaccessible on the inside can be moved to the outside of the molecule for use. Differentiation involves the temporary or permanent inhibition of genes that may be active in other cells.