Cell Cycle and Cell Division Flashcards
1
Q
Name one of the most fundamental characteristics of life
A
Cell division
2
Q
Why is cell division considered one of the most fundamental characteristics of life?
A
It is the method that enables life to perpetuate generation after generation
3
Q
The most conspicuous events occurring during cell divisions are all related to which organelle?
A
Chromosomes
4
Q
What ensures the normal functioning of the cells and through that, the life of the organism?
A
All body cells are the result of a long chain of repeated mitotic divisions; therefore, have the same type of chromosomes in the same number.
5
Q
When does the nucleus not appear to contain any particular thing inside?
A
When a normal unstained cell is observed under a light microscope
6
Q
When do several structures become noticeable in the nucleus?
A
When a normal cell is dyed with suitable dyes
7
Q
Name the discrete units of DNA
A
Chromosomes
8
Q
What is chromatin? Where is it found?
A
In each chromosome, there is one long DNA molecule associated with many proteins. This complex of DNA and proteins is called the chromatin
9
Q
How does the chromatin appear when the cell is not dividing?
A
The chromatin, under an electron microscope, appears to be in the form of a very long and extremely thin darkly stained fibre.
10
Q
Give the meaning of the term chromosome
A
Chroma: coloured, soma: body
11
Q
What happens to the chromatin as the cell prepares to divide?
A
The chromatin fibres coil and condense further, eventually becoming thick enough to be distinguished as separate chromosomes
12
Q
Define chromosomes
A
Chromosomes are highly coiled and condensed chromatin fibres
13
Q
Who studied chromosomes in animals? When?
A
A German scientist Walther Fleming first studied chromosomes in animals in 1882
14
Q
Where did the German scientist notice chromosomes?
A
In the rapidly dividing cells of the larvae of salamander
15
Q
How did the word mitosis come about?
A
In the larvae of the salamander, Flemming saw minute threads that appeared to be dividing lengthwise through an old microscope. Flemming called their division mitosis.
16
Q
What is the chromatin material that constitutes the fibre formed of?
A
It is formed of two substances :
- DNA (deoxyribonucleic acid)
- Histones
17
Q
What is the percentage of DNA in the chromatin material?
A
40%
18
Q
What is the percentage of histones in the chromatin material?
A
60 %
19
Q
Who first studied the shape of the DNA molecule?
A
Rosalind Franklin, in 1953
20
Q
Who worked out the structure of the DNA molecule?
A
Watson and Crick in 1953
21
Q
When were W & C awarded the Nobel Prize? For?
A
Watson and Crick proposed the double-stranded helical structure of DNA for which they were awarded the Nobel Prize in 1962
22
Q
What is another name for a single DNA molecule?
A
A macromolecule, since it is very large
23
Q
What is a single DNA molecule composed of?
A
Two complementary strands wound around each other in a double helix
24
Q
What is a single DNA strand composed of?
A
Repeating nucleotides
25
What is a nucleotide composed of?
Three components:
1. Phosphate
2. Sugar (pentose)
3. Nitrogenous base
26
Give the basic structure of a nucleotide
Phosphate, sugar arranged lengthwise, and a nitrogenous base attached inwards to the sugar which extends to join the complementary nitrogenous base from the other strand. Thus, the two strands together make a ladder-like arrangement, with the nitrogenous bases forming the "rungs" of the ladder
27
What forms the rungs of the ladder in a nucleotide?
The nitrogenous bases
28
How do the nitrogenous bases join?
By a hydrogen bond
29
How many nitrogenous bases are found in the DNA?
4
30
Name the 4 types of n. bases found in the DNA
1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)
4. Thymine (T)
31
Which nitrogen base pairs with which?
Adenine pairs with Thymine w/ two H₂ bonds (A=T)
| Guanine pairs with Cytosine w/ three H₂ bonds (G=C)
32
What are histones?
Histones are proteins that help in the coiling and packaging of DNA into structural units called nucleosomes
33
Name a core of eight histone proteins
Histone octamer
34
What is a nucleosome?
The structural unit in which DNA is coiled and packaged
35
Give the structure of a nucleosome
The DNA strand winds around a histone octamer - each such complex is called a nucleosome
36
How many nucleosomes may a single human chromosome have?
About a million nucleosomes
37
How many meters of DNA does a human cell contain?
Approximately 2 meters of DNA if stretched end to end
38
Give the diameter of the nucleus of a human cell
About 6 micrometers (6 µm) in diameter
39
Why does the DNA need to be condensed to fit inside the nucleus?
The human cells contains approximately 2 meters of DNA if stretched end to end but the nucleus of the human cell is about 6 micrometers (6 µm) in diameter
40
Which concept seen in a typical telephone cord is also seen in the chromatin fibres of chromosomes?
The concept of coiling and supercoiling
41
When is a chromosome visible?
During the start of cell division
42
What does a chromosome, in its visible state, consist of?
It consists of two sister chromatids joined at some point along the length
43
Name the point of attachment of the sister chromatids
The centromere
44
What does the centromere appear as?
A small constricted region
45
Where is each chromosome's centromere located?
At a particular site
46
Give the purposes of the centromere
1. A point of attachment of the two sister chromatids
2. Serves to attach to the spindle fibre during cell
division
47
What happens to the chromatids after cell division?
The chromatids are now called chromosomes and decondense and revert to their very long and fine thread-like chromatin fibres
48
How many chromatin fibres would be inside the nucleus?
The same as the no. of chromosomes that appear during cell division
49
Define genes
Genes are specific sequences of nucleotides on a chromosome, that encode particular proteins which express in the form of a particular feature of the body
50
What are genes the units of?
Heredity
51
What are genes responsible for?
For some specific characteristics of the offspring
52
What do new cells need to produced for?
1. Growth
2. Replacement
3. Repair
4. Reproduction
53
How is cell division essential for growth?
Most organisms begin their life as a single cell (the fertilized egg). This cell divides repeatedly to form a cluster of cells which start shaping for different functions to form tissues and organs.
54
How is cell division essential for replacement in the human body?
There is always a wear and tear of cells during the normal body functions. For example, 2 million RBCs in our body are destroyed every second. These are replaced by new cells formed through the division of their parent cells in the bone marrow.
55
Where are RBCs formed in the human body?
In the bone marrow
56
How is cell division essential for replacement in plants?
In plants, the old and dried leaves fall off and new ones grow out.
57
How is cell division essential for repair?
Apart from normal wear and tear of the tissues of the body, there may be accidental injuries. One may get cuts in the skin or fractures in the bone. Repair of such injuries is again through cells that divide, cover up the gaps, and join the broken ends.
58
Comment on the no. of chromosomes in cell divisions for growth, repair, and replacement
The no. of chromosomes remains the same at each division. The chromosomes duplicate and distribute equally in the daughter cells
59
Where does mitosis not occur?
In the egg producing oocytes, and sperm producing spermatocytes
60
Where does the no. of chromosomes remain the same?
In cell divisions for growth, repair, and replacement occurring in all body cells except the egg and sperm
61
Where does the egg produce oocytes?
In the ovaries
62
Where does the sperm produce spermatocytes?
In the testes
63
Name the organisms that reproduce only through mitosis
Amoeba or bacteria just divide to form two independent cells by mitosis
64
Name the organisms that reproduce through meiosis
Higher organisms like humans or in the banyan tree
65
What is the product of meiosis in humans?
Sperms and eggs
66
How many chromosomes do sperms and eggs receive?
They receive only half of the no. of chromosomes of their parent cells, i.e., one chromosome from each pair
67
Name the tasks a cell needs to complete to divide
1. Grow
2. Synthesize materials like RNA etc.
3. Duplicate its DNA
before physically splitting into its two daughter cells
68
Define cell cycle
The cell cycle is a series of organized, predictable events that take place in a cell leading to the duplication of its DNA and the subsequent division of the cell to produce two daughter cells.
69
Name the two phases of the cell cycle
1. a non-dividing phase called Interphase
2. a dividing phase called the M-phase or simply
mitosis
70
Describe the state of the cells in interphase.
The two daughter cells produced from a mother cell are relatively small, with a full-sized nucleus but relatively little cytoplasm. These cells are said to be in interphase.
71
What do the cells do in interphase?
During interphase, the cells prepare for the next cell division and grow to the same size as their mother cell
72
What was interphase formerly called?
IT was called the resting phase of the cell.
73
Why was interphase called the resting phase of the cell?
Since no change in chromosomes is visible externally during the interphase
74
Why is the term resting phase incorrect?
The cell is quite active during interphase in synthesizing more DNA
75
Name the three phases of the interphase
1. First growth phase
2. Synthesis phase
3. Second growth phase
76
What is synthesized in G1?
RNA and proteins are synthesized and the volume of cytoplasm increases
77
Which organelle divides in G1 (animal cells)?
Mitochondria
78
Which organelle divides in G1 (plant cells)?
Chloroplasts
79
Which organelles have their own DNA?
Mitochondria (in animal cells)
| Chloroplasts (in plant cells)
80
Which are the two paths in the late G1 phase?
The cells may either withdraw from the cell cycle and enter a resting phase [R]
OR
Start preparing for the next division by entering the next synthesis phase (S)
81
What occurs in the S phase?
More DNA is synthesized, the chromosomes are duplicated
82
In which phase is the cell ready to undergo cell division?
In the second growth phase (G2)
83
What happens in the second growth phase?
This is a shorter phase in which RNA and proteins necessary for cell division continue to be synthesized
84
What happens to the newly formed daughter after the dividing phase gets completed?
The newly formed daughter cells enter into interphase again and this way the cell cycle goes on & on
85
What happens to the DNA molecule during the S-phase?
Each DNA molecule (i.e., the chromosome) duplicates in readiness for their equitable distribution in the two daughter cells during mitosis.
86
What is the process of replication of DNA?
The double helix opens at one end, making the two strands free to which new strands begin to form and the process continues in sequence for the whole length of the DNA.
87
What does each new DNA contain?
One original strand and another new one
88
Can the cell cycle go on endlessly?
No. At some places, it stops permanently, at some places temporarily and at others till it is needed.
89
How does the cell cycle stop when needed?
There is a regulatory mechanism for cell cycles.
90
When does the cell cycle stop in the brain and other nerve cells?
Brain and other nerve cells, once formed in the embryo do not divide further. Once dead, they are not replaced
91
Comment on the cell cycle with reference to liver cells.
Liver cells may divide only once every one to two years to replace damaged or destroyed cells.
92
Comment on the cell cycle with reference to surface skin cells
Surface skin cells are continuously lost and replaced by the underlying cells.
93
What does a large portion of household dust contain?
Human skin cells
94
What does the powdery material that comes off from your skin on scratching or rubbing hard contain?
Dead skin cells
95
Comment on the cell cycle with reference to plants
In plants, the cells at the growing points (meristems) divide very rapidly and produce new leaves, buds and flowers, etc.
96
Comment on the cell cycle with reference to specialised germinal cells
Specialised germinal cells in the ovary and testis in animals and in the ovary and anthers in plants undergo the other type of cell division called meiosis to produce sex cells
97
What do uncontrolled non-stop cell cycles lead to?
Tumours that may or may not be cancerous
98
Why do we grow as children?
Because new cells are continuously being produced and they outnumber the dying cells
99
Why do we not grow as adults?
Our cell population stays constant. The number of new cells produced equals to the number of cells dying
100
What happens as we grow old?
The no. of new cells produced runs short of those that are dying
101
Name the two types of cell divisions
Mitosis
| Meiosis
102
Define mitosis
Cell division leading to the production of diploid cells for growth and development
103
Define meiosis
Cell division leading to the production of haploid cells or gametes (sperms or egg)
104
Where does mitosis take place?
In the somatic cells of the body
105
Give the meaning of mitosis
Mitosis : thread, referring to chromatin thread
106
What is the most important aspect of mitosis?
The same normal chromosome number is maintained at each cell division
107
In mitosis, what divides into what?
One parent cell divides into two identical daughter cells
108
Name the two phases of mitosis
1. Karyokinesis
| 2. Cytokinesis
109
What is Karyokinesis?
It is the first step of mitosis in which division of nucleus occurs
110
Name the four phases of Karyokinesis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
111
Are the four phases of mitosis similar in both animal and plant cells?
By and large, yes. But with a couple of differences
112
Is Karyokinesis a continuous process?
Each of the phases of Karyokinesis merges into the next phase making it a continuous process
113
Give the process of prophase
1. Chromosomes have become short and thick and are clearly visible inside the nucleus.
2. Each chromosome has already duplicated to form two chromatids
3. The two sister chromatids remain attached to each other at a small region called centromere
4. The centrosome (in animal cell) splits into two along with simultaneous duplication of centrioles contained in it. The daughter centrioles move apart and occupy opposite “poles” of the cell. Each centriole is surrounded by the radiating rays and is termed aster (star). (The animal cells may have either one or two centrioles)
5. A no. of fibres appear between the two daughter centrioles, which are called the spindle fibres
6. The nuclear membrane and the nucleolus disappear.
7. The duplicated chromosomes start moving towards the “equator” of the cell.
114
What are poles?
Poles means the extremities of an axis
115
What is equator?
The middle plane dividing the cell into similar halves
116
Give the process of metaphase
1. The duplicated chromosomes arrange on the equatorial plane. Each chromosome gets attached to a spindle fibre by its centromere
117
Give the process of anaphase
The centromere attaching the two chromatids divides and the two sister chromatids of each chromosome separate and are drawn apart towards the opposite poles. The drawing action is performed by the spindle fibres.
118
Give the process of telophase
1. Each chromatid or the daughter chromosome lengthens, becomes thinner and turns into a network of chromatin threads
2. Nuclear membrane reappears
3. Nucleolus reappears in each daughter nucleus
119
What happens to all the contents of the cytoplasm during karyokinesis?
All the contents of the cytoplasm including the mitochondria and also the chloroplasts (in plant cell) are randomly distributed in the daughter cells during karyokinesis
120
Define cytokinesis
The division of the cytoplasm leading to the formation of two daughter cells
121
How does cytokinesis occur in animals?
At the end of telophase, a cleavage furrow appears in the cell membrane in the middle which deepens and splits the cytoplasm into two, thus producing two daughter cells.
122
How does cytokinesis occur in plants?
The cell plate laid down at the equatorial plane grows from centre to periphery, resulting in two cells.
123
What are all the nuclear changes that occur during cell division collectively termed?
Karyokinesis (karyo : nucleus)
124
Differentiate between mitosis in animal cells vs in plant cells
1. Asters are formed vs asters are not formed.
2. Cytokinesis by furrowing of cytoplasm. The furrow starts from cell membrane which then proceeds to the centre of the cell VS cytokinesis by cell plate formation. The cell plate is laid down at the centre of the cell which then grows and extends towards the cell membrane.
3. Occurs in most tissues throughout the body (for growth and replacement) VS occurs mainly at the growing tips (for lengthening) and sides (for increase in girth)
125
Which two expressions are used incorrectly with reference to cell division but are incorrect?
The terms Parent and Daughter cells, because the “parent” cell loses its identity in the process, and the “daughter” cells are not necessarily feminine
126
Give the significance of mitosis
1. Growth
2. Repair
3. Replacement
4. Asexual reproduction
5. Maintains same chromosome no. in daughter cells
127
How does mitosis help in replacement?
Replacement of old and dead cells such as the replacement of the blood cells and the epidermal cells of the skin
128
How does mitosis help in asexual reproduction?
Asexual reproduction in which the unicellular organisms, such as amoeba or the yeast cell, divide into two
129
Which two organelles have their own DNA?
Bohr mitochondria and chloroplasts
130
What do the two organelles contain that help in producing their particular proteins?
They contain their own ribosomes
131
How do the two organelles divide?
The two divide on their own by simple fission, just splitting into two and are partitioned between the two daughter cells produced by mitosis
132
What is mitochondrial division guided by?
By the genes in the nucleus and through the cytoplasmic ribosomes
133
Name three cells which last a lifetime but once dead, cannot be replaced
Cells of the eye lens, nerve cells of the cerebral cortex and most muscle cells
134
How old are skin cells?
Replaced every two weeks or so
135
How old are RBCs?
last for about 130 days and are replaced
136
How old are bone cells?
Replaced every 10 years or so in adults
137
How old are epithelial cells lining the gut ?
Epithelial cells lining the gut last only 5 days
138
How old are gut cells other than epithelial cells?
15 years
139
How old are liver cells?
Replaced every 300-500 days
140
What does meiosis produce?
The sex cells or gametes
141
Where does meiosis take place in animals?
In the reproductive organs (testis and ovary) to produce sperms and ova
142
Where does meiosis take place in plants?
In the following plants, in the bathers and the ovule to produce pollen grains and the female gametophyte
143
Give the meaning of meiosis
Diminution
144
Give the most significant aspect of meiosis
No. of chromosomes in the sex cells is halved
145
What is haploid and diploid number expressed as?
Haploid - n, Diploid - 2n
146
Why is only one member of each pair of chromosomes in humans passed on to the sex cells?
Out of the 23 pairs of chromosomes in humans, only single chromosomes i.e. one member of each pair (haploid) are passed on to the sex cells. This is essential because when the male and female gametes fuse during fertilisation, the normal double (diploid) no. is reacquired
147
What are the two stages of meiosis?
The reduction division, and the mitotic division.
