B DNA and Cell Division Flashcards

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

What is the structure of DNA?

A
  • A polymer made of nucleotides that contain a pentose sugar (deoxyribose), a phosphate group and a base.
  • Mononucleotides are joined by condensation reactions, forming a phosphodiester bond between the pentose sugar of one monomer and the phosphate group of another monomer.
  • A DNA molecule consists of two polynucleotide strands, twisted to form a double helix, each helix has a sugar-phosphate backbone, with the central bases joined by hydrogen bonds.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the two different types of bases in DNA?

A
  • Thymine and cytosine are pyrimidines.
  • Guanine and adenine are purines.
  • Adedine and thymine form 2 hydrogen bonds between each other, cytosine and guanine form 3 hydrogen bonds between each other.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How does the structure of DNA correspond to its function?

A
  • Bases in sequence code for amino acids, therefore the base sequence stores genetic information.
  • DNA is very large so can store a massive amount of information.
  • DNA’s helix makes it compact.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How is DNA extracted from cells?

A

DNA purification:
1. Grind the sample to break down cell walls.
2. Add to a test tube and mix with a detergent to break down the nuclear envelopes.
3. Add protease (to break down proteins that are attached to DNA).
4. Add ethanol (causes DNA to precipitate as a white solid).
5. Extract DNA with a glass rod.

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

Compare eukaryotic and prokaryotic DNA:

A
  1. Eukaryotic DNA contains exons and introns, whereas prokaryotic DNA only contains exons.
  2. Eukaryotic DNA and histones form chromosomes, whereas prokaryotic DNA cannot form chromosomes.
  3. In eukaryotes DNA is also found in mitochondria and chloroplasts (as short, circular DNA that is not associated with chromosomes).
  4. Some prokaryotes have small, circular DNA that lies free in the cytoplasm called plasmids, which replicate independently.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How are chromosomes formed?

A
  • DNA condenses into chromatin, by wrapping tightly around histones, enabling it to fit into the nucleus.
  • Chromatin folds together to form a chromatid.
  • Sister chromatids are then joined at the centromere to form a chromosome.
  • The end of each chromatid has a telomere which stops the DNA from degrading.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is binary fission?

A

The process by which prokaryotic cells divide:
1. The single, circular DNA is replicated (any plasmids present are also replicated).
2. The cytoplasm divides, forming two daughter cells, these may have different numbers of plasmids, but each have a copy of the circular DNA.

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

How do viruses replicate?

A
  • They are not cells so do not undergo cell division.
  • They inject their nucleic acid into host cells and the host cell then replicates the virus particles.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is interphase?

A
  • The longest stage of the cell cycle that gets the cell ready to divide.
  • During G1 (growth 1) the cell grows in size and synthesises new organelles and proteins.
  • During synthesis, DNA is replicated.
  • During G2 the cell continues to grow in size and new proteins/organelles are synthesised.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the checkpoints during interphase?

A
  • G1 checkpoint checks cell size, that there are enough proteins and organelles and that DNA isn’t damaged.
  • G2 checkpoint checks that DNA has been replicated correctly.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What occurs during mitosis?

A

The nucleus divides in two - DNA has already been replicated is the mass of DNA and the mass of the cell remains unchanged.

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

What occurs during cytokinesis?

A

The cell divides in two, creating two genetically identical daughter cells.

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

Which cells enter the G0 phase?

A
  • Cells that don’t divide eg. differentiated cells
  • Cells that fail to pass the G1 checkpoint (which prevents mutated cells from dividing).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the functions of mitosis?

A
  1. Growth (from a zygote to a multicellular organism)
  2. Repair (damaged cells can be quickly replaced by genetically identical cells)
  3. Reproduction (enables asexual reproduction and produces gametes from haploid cells for sexual reproduction).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the mitotic index?

A

The ratio between the number of cells undergoing mitosis in the population, with the total population of cells.

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

What are the stages of mitosis?

A
  1. Prophase:
    - Chromatin condenses into chromosomes (visible under a microscope).
    - The nucleolus disappears and the nuclear envelope breaks down, leaving chromosomes lying free in the cytoplasm.
    - Spindle fibres form at the centrosomes (poles of the cell) - each centrosome contains centrioles that develop the spindle fibres.
  2. Metaphase:
    - Spindle fibres attach to the centromeres.
    - Chromosomes line up along the equator of the cell - each sister chromatid is attached to opposite poles.
    - There is a checkpoint during metaphase to check that all chromosomes are attached to spindle fibres and are aligned.
  3. Anaphase:
    - Spindle fibres shorten, pulling chromatids to opposite ends of the ell.
  4. Telophase:
    - At the cells poles, chromatids decondense back into chromatin.
    - The nuclear envelope and nucleoli reform and spindle fibres break down - leaving two fully developed nuclei at each pole of the cell.
17
Q

How does DNA replication occur?

A
  1. DNA helicase moves along the DNA molecule, breaking hydrogen bonds between complementary base pairs.
  2. DNA nucleotides lying free in the nucleus are attracted to the exposed complementary bases, forming hydrogen bonds between the bases (each DNA strand acts as a template).
  3. DNA polymerase then attaches to each strand, joining the new nucleotides together by forming phosphodiester bonds in a condensation reaction.
  4. Once the two identical molecules of DNA are produced, they coil to form helix’s.
18
Q

What are the benefits of semi-conservative replication?

A
  • DNA stands are completely separated, allowing each stand to act as a template for a second to form. Since nucleotides are attracted to complementary bases there is a much greater chance that the right nucleotide will be added in the right place.
  • Whereas in the conservative and dispersive models, the wrong base pairs could be added/the wrong chunks of DNA bind together, meaning the DNA is not identical, which could lead to cell death.