The Mitotic Cell Cycle + Chromosomes (Chapter 5) Flashcards Preview

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What is a chromosome?

A thread-like structure made up of DNA


What is the structure of the chromosome during interphase?

The chromosome is a double structure made of two identical structures called chromatids, joined together
- the two chromatids are held together by a narrow region called the centromere which can be found anywhere along the length of the chromosome


Why is a chromosome made up of two identical chromatids during interphase?

Because during this period, each DNA molecule in a nucleus makes an identical copy of itself
- each chromatid contains one of these DNA copies


How many DNA molecule does each chromosome contain?



What is DNA?

The molecule of inheritance made up of a series of genes


What is a gene?

A section of a DNA molecule that codes for a particular polypeptide


What happens when cells divide?

One chromatid goes into one daughter cell and the other chromatid goes into the other daughter cell, making the daughter cells genetically identical (bc chromatids, therefore DNA, therefore genes are identical)


How is DNA stored?

It is wound around the outside of basic protein molecules called histones which prevent knots in DNA


Why is DNA wrapped around histones?

Because DNA is a very long molecule (total length in cell = 1.8m) and has to be packed into the nucleus (6μm diameter)


Why do histones interact easily with DNA?

Because they are basic and DNA is acidic


What is chromatin?

The mixture combination of DNA and histones, which is very highly condensed by coiling


What are chromosomes made of?



What is mitosis?

Nuclear division that produces two genetically identical daughter nuclei, each containing the same number of chromosomes as the parent nucleus


What is the cell cycle?

The regular sequence of events that takes place between one cell division and the next


What are the three phases of the cell cycle?

Nuclear division
Cell division


What happens during interphase?

The cell grows to its normal size after cell division and carries out its normal functions, synthesising many substances (esp proteins) in the process


What are the phases of interphase?

G1, S and G2


What happens during the S (synthesis) phase of interphase?

1) At some point during interphase, a signal may be received that the cell should divide again
2) If this happens, the DNA in the nucleus replicates so that each chromosome consists of two identical chromatids - relatively short phase


What happens during the G1 phase?

1) During G1, cells make the RNA, enzymes and other proteins needed for growth
2) At the end of G1, the cell becomes committed to dividing or not dividing (restriction point)


What happens during the G2 phase?

1) The cell continues to grow and new DNA is checked and any errors are usually repaired
2) Preparations are made to begin the process of division e.g. there is a sharp increase in production of the protein tubulin which is needed to make microtubules for the mitotic spindle and centrioles are doubled


What phase follows interphase?

Nuclear division (M phase, M=mitosis)


What happens to growth during mitosis?

It stops temporarily


What happens after the M phase?

The whole cell divides to create two genetically identical cells


How does cell division occur in animal cells?

By cytokinesis


How does cell division occur in plant cells?

It involves the formation of a new cell wall between the two new nuclei


How long does the cell cycle last?

It is very variable, depending on environmental conditions and cell type (but normally hours)


Even though mitosis is continuous, what are the four main stages?



Although the behaviour of chromosomes is identical to animal cells, how is nuclear/cell division different?

1) Plant cells do not contain centrosomes (or centrioles)
2) A new cell wall must form between the daughter nuclei


What happens during early prophase?

(Centrosomes replicate just before prophase)
1) Chromosomes start to appear as the chromatin condenses (coils up), becoming shorter and thicker
(The nucleolus and nuclear envelope are intact)


What happens during late prophase?

1) The nuclear envelope and nucleolus disappear (disaggregate), making more space
2) Chromosomes are formed, made of twin chromatids
3) Centrosomes move to the opposite ends of the nucleus where they form the poles of the mitotic spindle, which is formed at the end of prophase

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