Cell and nuclear division Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Why do all organisms need to produce new cells?

A

For growth, maintenance and reproduction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do cells produce new cells?

A

Through cell division.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is cell division in simple terms?

A

When one cell divides into two.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a mother cell?

A

The cell that divides.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the daughter cells?

A

The cells that are produced from the mother cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What happens to the mother cell during cell division?

A

It disappears as a whole in the process, unlike reproduction by animal parents.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a theory that has strong evidence behind it in terms of when new cells are produced?

A

There is strong evidence for the theory that new cells are only ever produced by division of a pre-existing cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What evidence is there for the theory that new cells are only ever produced by division of a pre-existing cell

A

If we consider the trillions of cells in our bodies, each one was formed when a pre-existing cell divided in two. We can trace this back to the original cell, which is the zygote. The zygote was the start of our individual lives, was produced by the fusion of a sperm and egg.

Sperm and egg cells were produced by cell division in our parents. The origins of all cells in our parents’ bodies goes back to the zygote from which they developed and then on through all previous generations of human ancestors. If we accept that humans evolved from pre-existing ancestral species, we can trace the origins of cells back through hundreds of millions of years to the earliest cells on Earth. This means there is a continuity of life from its beginnings to the cells in our bodies today.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens in cytokinesis?

A

The cytoplasm of a cell is divided between two daughter cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is cytokinesis apart of?

A

Cytokinesis is a part of cell division, along with nuclear division by mitosis or meiosis.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When can the process of cytokinesis begin?

A

As soon as chromosomes have separated and are far enough apart to ensure that none of them end up in the wrong cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does cytokinesis do?

A

All the cytoplasm and its contents of the mother cell are shared out between the daughter cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is one difference between plant and animal cells?

A

They carry out cytokinesis differently.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Explain how cytokinesis occurs in animal cells?

A

In animal cells, the plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow. This is accomplished using a ring of contractile proteins immediately inside the plasma membrane, usually at the equator. The contractile proteins are actin and myosin and are similar to those that cause contraction in muscle. When the cleavage furrow reaches the centre, the cell is pinches apart into 2 daughter cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain how cytokinesis occurs in plant cells?

A

In plant cells, microtubules are built into a scaffold straddling the equator, which is used to assemble a layer of vesicles. The vesicles fuse together to form plate-shaped structures. With the fusion of more vesicles, two complete layers of membrane are formed across the whole of the equator of the cell. They become the plasma membranes of the 2 daughter cells adjacent to the new dividing walls. they are connected to the existing plasma membranes at the sides of cell, completing the division of the cytoplasm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the stage that occurs in plants after cytokinesis?

A

The next stage in plants is for pectins and other substances to be brought in vesicles and deposited by exocytosis between the 2 new membranes. this forms the middle lamella that will link to the new cell walls. Both daughter cells then bring cellulose to the equator and deposit it by exocytosis adjacent to the middle lamella. As a result, each cell builds its own cell wall across the equator.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does cytokinesis generally do?

A

In many cases, cytokinesis divides the cytoplasm of the mother cell into equal halves.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do cells split equally?

A

This happens in a growing root tip. Root growth is due to enlargement and division of cells arranged in columns. The cells in a column all differentiate in the same way, so cytoplasm is apportioned equally when they divide.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why can unequal division occur?

A

Cytoplasm is sometimes divides unequally. Small cells produced by unequal division can survive and grow if they recieve a nucelus and at least one of each organelle that cannot be assembles from components in the cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

3 examples of unequal division

A

For example, mitochondria can only be produced by division of a pre-existing mitochondrion, so there must be at least one mitochondrion in a daughter cell for it to be viable. Another example of unequal division are budding in yeast and oogenesis in humans.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is budding?

A

Yeast cells reproduce asexually, and this process in called budding.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Explain budding in yeast

A

The nucleus divides by mitosis. A small outgrowth of the mother cell is formed. It receives one of the nuclei, but only a small share of the cytoplasm. A dividing wall is constructed, separating the 2 cells. The small cell then splits away, leaving a scar where it was attached to the larger cell. Yeast cells carry out this budding process repeatedly and do not have to double in size between each division.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How are sperm and eggs produced in humans?

A

The production of both sperm and eggs in humans starts with 2 division of a mother cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Explain what happens during sperm production

A

During sperm production, the cytoplasm is divided equally in the first and second divisions, resulting in four, equally sized small cells, each of which develops into a mature sperm.

25
Q

One difference between the use of eggs and sperm

A

Large numbers of sperm are needed in humans, but only one egg (oocyte) is needed.

26
Q

Why is the egg cell much larger than a sperm cell?

A

Because it contains the food needed to sustain the developing embryo.

27
Q

Why is there unequal division during oogenesis?

A

Because large numbers of sperm are needed in humans, but only one egg is produced at a time. Therefore, unequal division of cytoplasm occurs during oogenesis.

28
Q

Explain the 2 divisions that occur in oogenesis in humans

A

The first division produced one large cell with nearly all cytoplasm and a small polar body which does not develop further. Only the large cell carries out the second division, with unequal division of the cytoplasm again resulting in one large cell and one very small polar body. The large cell develops into a mature oocyte that is ready for fertilization.

29
Q

What would happen if a cell divided without first undergoing nuclear division?

A

One daughter cell has the nucleus and the other would be anucleate (without a nucleus)

30
Q

Why are anucelates bad?

A

Because anucleate cells cannot synthesize polypeptides, so they cannot grow or maintain themselves. They have limited lifespans.

31
Q

Example of an anucleate cell?

A

Red blood cells, which have no nucleus, survivre for about 120 days.

32
Q

What process do all cells undergo?

A

To produce extra nuclei before cell division, cells undergo either mitosis or meiosis. These two types of nuclear divison, have different roles, so most organisms use both during their life cycle.

33
Q

What is mitosis used for?

A

It’s used to produce genetically identical cells.

34
Q

What is the number of diploid chromosomes in humans?

A

23

35
Q

Roles of mitosis in eukaryotes

A
  • Cells produced using mitosis have the same number of chromosomes as the parent cell, so the number of chromosomes is maintained
  • Cells produced by mitosis have the same genes as the parent cell, so mitosis maintains the genome. This ensures that every cell in a multicellular organism has all the genes it needs. It also ensures that the cells in an individual are genetically identical, preventing problems such as tissue rejection.
  • Mitosis allows a successful genome to be inherited without changes by offspring in asexual reproduction.
36
Q

Roles of meiosis eukaryotes

A
  • Cells produced using meiosis have half as many chromosomes as the parent one. Division of a nucelus with 2 sets of chromosomes (diploid) results in nucleic with only one set (haploid). This is essential to produce haploid gametes from diploid germ cells in sexual life cycles.
  • Pairs of genes in a diploid mother cell are dealt randomly to daughter cells, so there are almost limitless numbers of possible combinations. Meiosis therefore generates variation and genetic diversity allowing evolution by natural selection.
37
Q

What is meiosis used for?

A

Meiosis is used to halve the number of chromosomes from diploid to halpoid and to generate genetic diversity.

38
Q

What does a cell preparing for nuclear division do by mitosis or meisois do?

A

Replicates all the DNA. This ensures that each daighter cell produced receives a full complement of genes, allowing it to perform any function requires.

39
Q

Before replication, what is the DNA within the nucleus called and exists as?

A

Before replication, the DNA within the nucleus exists as long single molecules called chromosomes.

40
Q

What happens after replication of the DNA?

A

After replication, there are pairs of identical DNA molecules. These identical DNA molecules are still considered to be part of the same chromosome and they are held together by loops of a protein complex called cohesin. The cohesin loops are not cut until the start of anaphase during mitosis or meiosis.

41
Q

Chromosomes, chromatids and cohesion loops at each stage of mitosis or meiosis

A

Early interphase - single chromatid before DNA replication. During interphase it would be much more elongates.

Prophase - chromosomes with 2 chromatids held together by cohesin lops in prophase of mitosis.

Metaphase - microtubules attach to centromeres pull on chromatids but cohesin holds them together.

Anaphase - cohesin loops have been cut, so sister chromatids can separate and be pulled to opposite pulls.

42
Q

What happens when DNA is elongated?

A

Chromosomes are too narrow to be seen with a light microscope. They gradually become shorter and fatter during the early stages of mitosis or meiosis and are then visible. Eventually each chromosome can be seen to have 2 strands, called chromatids.

43
Q

What does each chromatid contain?

A

Each chromatid contains a single very long DNA molecule, produced by DNA replication from an original molecule.

44
Q

Explain what sister chromatids and non-sister chromatids are?

A

The 2 strands in a chromosome are therefore known as sister chromatids and they are genetically identical. Strands on different chromosomes are non-sister chromatids and do not usually have identical genes.

45
Q

Where do the chromosomes move during mitosis and meiosis?

A

During mitosis and meiosis, chromosomes are moved to opposite poles of the cell, so they can become part of separate nuclei. The DNA molecules in these chromosomes are immensely long. For example, the average length in human chromosomes is more than 50,000 nanometers and the nucleus is less than 5 nanometers wide.

46
Q

How are the chromosomes move to opposite poles?

A

To separate and move molecules as elongated as this without knots, tangles or breaks they must be packages into much shorter structures. This condensation of chromosomes and their subsequent movement is therefore an essential feature of mitosis and meiosis.

47
Q

How are chromosomes condenced?

A

Chromosomes are condensed by being made shorter

47
Q

How is the initial shortening carried out?

A

An initial shortening is carried out by wrapping the double helix around the histone, to form nucleosomes together. There are several morestages to condense the chromosomes but they’re not yet fully understood.

48
Q

How are chromosomes moved?

A

By using microtubules. This is a hollow cylinder of tubulin proteins that can be rapidly assembled or disassembled.

49
Q

During interphase what do microtubules do?

A

During interphase, microtubules serve a variety of functions including acting as a cytoskeleton.

50
Q

What are happens to some microtubules in the early stages of mitosis?

A

Some of these microtubules are disassembles in the early stages of mitosis and are reassembles by microtubule organizing centers (MTOCs) at the poles of the cel, which link tubulin molecules together.

51
Q

How do microtubules form?

A

Microtubules are assembled that reach the equator of the cell, forming a spindle-shaped aray. At the same time, protein structures called kinetochores are assembled on the centromere of each chromatid. Some of the growing microtubules link up with these kinetochores and some attach to other microtubules from the opposite pole.

52
Q

What does the kinetochore act as?

A

The kinetochore acts as a microtubule motor by removing tubulin subunits from the attached ends of the microtubules. This shortens the microtubules linking the kinetochores to the poles, putting them under tension.

53
Q

What is initially holding the chromatids together?

A

Initially in mitosis the chromatids do not move because loops of cohesion hold them together.

54
Q

What can happen as soon has cohesion has been cut?

A

As soon as the cohesion has been cut, shortening of the spindle microtubules by the kinetochores causes sister chromatids to move to opposite poles. In meiosis, homologous chromosomes are initially held together by know-like structures called chiasmata, but when these have slid to the ends of the chromosomes, movement to opposite poles can begin.

55
Q

What are the 4 stages of mitosis?

A
  1. Prophase - the starting phase with condensation of chromosomes (pro = before)
  2. Metaphase - the phase after condensation with chromosomes released from the nucleus ( meta = after)
  3. Anaphase - a brief phase during which the chromosomes are moved up to poles from the equator (anaphase = up)
  4. Telophase - the final phase in which nuclei reform and chromosomes decondnse (telos = finally)
56
Q

Explain interphase preceding mitosis

A
  • The chromosomes are dispersed through the nucleus so are not individually discernible (not easily visible)
  • To prepare for mitosis, all of the DNA is replicated and each chromosome then consists of 2 very elongated chromatids containing identical DNA
57
Q
A