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Y11 Biology 2025 > Cell cycle > Flashcards

Cell cycle Flashcards

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1
Q

Why do cells need to replicate?

A

for growth, repair and replacement as well as reproduction.

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2
Q

What are chromosomes?

A

Thread-like structures composed of DNA and associated proteins (histones) containing many genes at specific loci.

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3
Q

What is the function of DNA?

A

DNA controls various cellular functions by coding for functional proteins.

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4
Q

What is DNA replication?

A

The process by which DNA makes an exact copy of itself.

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5
Q

Why is it important for DNA replication to take place before a cell divides?

A

All cells need DNA to be able to make proteins.

When a cell (the parent cell) divides into two daughter cells, each daughter cell must inherit the full set of DNA from the parent cell.

If this wasn’t the case, the daughter cells wouldn’t be able to make all the necessary proteins for their survival.

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6
Q

Define DNA replication

A

Helicase unwinds and unzips the DNA double helix, separating the two parent strands of the DNA molecule from one another by breaking the hydrogen bonds between complementary base pairs.

Each strand then acts as a template for synthesizing a new strand of DNA. RNA primase adds an RNA primer at the 3’ end so DNA Polymerase can attach to the template strands.

Then DNA Polymerase copies the DNA template strands, moving 3’ to 5’, by joining up free DNA nucleotides by complementary base pairing.

DNA ligase joins any gaps in the sugar phosphate backbone of the Okazaki fragments . Two identical copies of DNA are produced.

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7
Q

What does it mean by semi-conservative theory of replication?

A

It means that a newly formed DNA molecule consists of one original strand and one newly synthesized strand.

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8
Q

What is the function of helicase in DNA replication?

A

Helicase unwinds and unzips the DNA double helix, separating the two parent strands of the DNA molecule from one another by breaking the hydrogen bonds between complementary base pairs.

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9
Q

In what direction does the leading template strand run?

A

3’ to 5’ in the same direction Helicase moves along the DNA.

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10
Q

In what direction does the lagging template strand run?

A

5’ to 3’ in the opposite direction to the movement of Helicase.

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11
Q

What is the function of RNA primase?

A

RNA primase adds an RNA primer at the 3’ end so DNA Polymerase can attach to the template strands.

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12
Q

What is an RNA primer and what is its function?

A

An RNA Primer is a short sequence of RNA nucleotides (5~10 nucleotides long) that is complementary to the template strand.

It provides an attachment site for DNA polymerase.

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13
Q

What is the function of DNA polymerase?

A

DNA Polymerase copies the DNA template strands, moving 3’ to 5’, by joining up free DNA nucleotides by complementary base pairing

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14
Q

Along the leading template strand, in which direction does DNA polymerase move with respect to Helicase?

A

The same direction as Helicase.

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15
Q

Along the lagging template strand, in which direction does DNA polymerase move with respect to Helicase?

A

In the opposite direction to helicase.

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16
Q

What is the function of ligase?

A

To join Okazaki fragments by forming phosphodiester bonds between neighbouring nucleotides.

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17
Q

How does the structure of DNA enable it to be easily replicated?

A

Double stranded - unwind DNA to provide template strands

Weak hydrogen bonds - easily broken to expose base pairs

Complementary base pairing - enables exact copy of DNA to be made

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18
Q

What is the process by which prokaryotes replicate/reproduce?

A

Binary fission

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19
Q

What are the four main steps in binary fission in prokaryotes?

A

Step 1: DNA replication. Step 2: Elongation. Step 3: Septum formation. Step 4: Cytokinesis

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20
Q

State what happens during Gap 1 stage.

A

Cell growth, Production of enzymes involved in DNA replication, Normal cellular functions.

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21
Q

State what happens during Gap 2 phase.

A

Cell growth/ Normal cellular functions/ Preparation for mitosis (producing proteins involved in mitosis).

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22
Q

State what happens during Synthesis phase.

A

DNA replication

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23
Q

Which phase of the eukaryotic cell cycle is longest?

A

Interphase, which consists of G1, S and G2 phases.

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24
Q

If a cell is diploid, it contains ….

A

two complete sets of chromosomes, one set from each parent/ pairs of homologous chromosomes

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25
Q

If a cell is haploid, the cell contains …..

A

only one complete set of chromosomes.

26
Q

What is the main difference between a non-replicated chromosome and a replicated chromosome.

A

A non-replicated chromosome is made of one copy of DNA molecule, whereas a replicated chromosome is made of two identical copies of DNA molecule.

27
Q

List the stages in Mitosis

A

Prophase, Metaphase, Anaphase and Telophase

28
Q

State what happens during prophase.

A

DNA condense into chromosomes and become visible.
Nuclear membrane disappears.
Centrosomes migrate to two opposite poles of the cell.

29
Q

State what happens during metaphase.

A

Chromosomes align along the equator of the cell.

Spindle fibres attach to the centromeres of the chromosomes.

30
Q

State what happens during anaphase.

A

Sister chromatids pulled apart to opposite poles of the cell by spindle fibres.

31
Q

State what happens during telophase.

A

Two new nuclear membranes form.
Cleavage furrow starts to form (where plasma membrane starts to invaginate or fold inwards). This only occurs in animal cells.
In plant cells, a cell plate begins to form.

32
Q

What happens during cytokinesis?

A

Division of the cytoplasm in the parent cell which leads to the formation of the two daughter cells that are genetically identical to each other and to the original parent cell. This occurs after mitosis.

33
Q

What are stem cells?

A

Stem cells are non-specialised cells that can divide and differentiate into different specialised cells.

34
Q

What does it mean by stem cell potency?

A

Some stem cells can differentiate into any cell types, while others can only differentiate into a limited number of cell types – this varying capacity to differentiate is referred to as ‘stem cell potency’.

35
Q

State two main types of stem cells.

A

Adult stem cells and Embryonic stem cells.

36
Q

Arrange the following levels of stem cell potency from least potency to greatest potency.

Multipotent, Totipotent, and Pluripotent.

A

Multipotent -> Pluripotent -> Totipotent

37
Q

Where in the body can you find adult stem cells?

A

Tissues found in different organs.

38
Q

What is the potency of adult stem cells?

A

Multipotent. Adult stem cells can only give rise to a limited number of cell types.

39
Q

What is the potency of embryonic stem cells?

A

Pluripotent. They can give rise to all cell types in the body except the ones that form the placenta.

40
Q

What is the potency of embryonic stem cells?

A

Pluripotent. They can give rise to all cell types in the body except the ones that form the placenta.

41
Q

What is the term that is used to refer to an embryo that is 5 days old and consists of two groups of cells: Trophoblast and Inner cell mass?

A

Blastocyst

42
Q

Why are embryonic stem cells considered more useful for medical research?

A

Because they have a higher level of potency then they can differentiate into a wider range of cell types in the body and therefore are more useful to scientists.

43
Q

State ethical issues that were caused by the use of stem cells in medical settings.

A

Issue 1: Human embryos are destroyed when embryonic stem cells are extracted.

Issue 2: Offering unproven stem cell therapies to those who are desperate.

44
Q

What is apoptosis?

A

Apoptosis is regulated, programmed cell death

45
Q

Why is apoptosis important in multicelluar organisms?

A

It allows old and/or damaged cells to be removed in your body.
It allows virally infected cells to be removed in your body.
It allows unnecessary/unwanted cells to be removed during embryonic development.

46
Q

How is apoptosis triggered in a cell?

A 
Mitochondrial pathway (intrinsic)
Death receptor pathway (extrinsic)
47
Q

Once a cell receives signals for apoptosis, what is the group of enzymes that is activated in the cell?

A

Caspase enzymes.

48
Q

What do caspase enzymes do to bring about the programmed cell death in a target cell?

A

Once activated, caspase enzymes cleave specific proteins within the cell, which leads to the breakdown of organelles. This will eventually lead to the formation of apoptotic bodies.

49
Q

outline the pathway of what happens to the cell as its intracellular materials continue to be broken down by activated caspase enzymes.

A

Cell shrinkage -> Blebbing -> Formation of apoptotic bodies.

50
Q

Following apoptosis, describe how apoptotic bodies are removed

A

phagocytosis. This means that apoptotic bodies are recognised, engulfed and destroyed by phagocytes

51
Q

If a cell fails to pass any of the checkpoints during the cell cycle, what will happen to the cell?

A

The cell will try to fix the issue (e.g. repairing DNA damage) first. If the issue cannot be fixed, then the cell will undergo apoptosis.

52
Q

What is checked during G1 checkpoint?

A

Checking for DNA damage and Cell size.

53
Q

What is checked during G2 checkpoint?

A

check that DNA has correctly replicated in the S phase.

54
Q

What is checked during Metaphase checkpoint?

A

check that spindle fibres have correctly attached to the centromeres of replicated chromosomes.

55
Q

Tumours can be classified into which two categories?

A

Benign and Malignant

56
Q

Tumours can be classified into which two categories?

A

Benign and Malignant

57
Q

State two characteristics of benign tumours.

A

Any two of the following:

  1. Relatively slow-growing.
  2. Cells in a benign tumour tend to stay together within a capsule.
  3. Benign tumour cells usually retain their original cell shape and structure.
58
Q

State two characteristics of malignant tumours.

A

Any two of the following:

  1. Fast growing.
  2. can spread to other parts of the body via the bloodstream or lymphatic system.
  3. malignant tumour cells (aka cancer cells) have lost their original cell shape and structure.
59
Q

Define cancer

A

Uncontrolled unregulated cell division (too much mitosis)

60
Q

Define Necrosis

A

Premature cell death

Y11 Biology 2025 (16 decks)

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