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Biology A-level > T3 - Voice of the genome > Flashcards

T3 - Voice of the genome Flashcards

1
Q

What happens during fertilisation?

A
  1. Acrosome reaction:
    - The sperm cell and ovum cell-surface membrane fuses
    - The sperm cell binds to receptors on the zona pellucida
    - The acrosome fuses with its own cell-surface membrane
    - Hydrolytic digestive enzymes are released
    - The zona pellucida is broken down
  2. Cortical reaction:
    - The cortical granules fuse with the cell-surface membrane
    - Chemicals are released
    - The zona pellucida hardens
    - Polyspermy is avoided
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2
Q

Compare mitosis and meiosis

A

Similarities:
- Both mitosis and meiosis involve cell division.
- Both mitosis and meiosis synthesize DNA.

Differences:
- Mitosis produces two diploid cells, whilst meiosis produces four haploid .
- Mitosis takes place all over the body, whilst meiosis only takes place in sex organs.
- Mitosis does not produce genetic variation, whilst meiosis creates genetic variation.
- Mitosis produces two daughter cells, whilst meiosis produces four unidentical cells.

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3
Q

What are the stages of mitosis?

A
  1. Interphase
  2. Prophase
  3. Metaphase
  4. Anaphase
  5. Telophase
  6. Cytokinesis
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4
Q

What happens in the interphase of mitosis?

A
  1. G1 phase - increase in cytoplasm and cell membrane
  2. S phase - DNA replication takes place
  3. G2 phase - cell organelles replicate
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5
Q

What happens in the prophase of mitosis?

A
  1. Chromosomes condense (supercoil) to become shorter and fatter
  2. Spindle fibres form
  3. Nuclear membrane breaks down
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6
Q

What happens in the metaphase of mitosis?

A
  1. Spindle fibres attach to the centromeres of chromosomes
  2. Chromosomes line up at equator
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7
Q

What happens in the anaphase of mitosis?

A
  1. Sister chromatids are separated as the spindle fibres shorten
  2. Sister chromatids are pulled to opposite poles
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8
Q

What happens in the telophase in mitosis?

A
  1. Chromosomes decondense (uncoil)
  2. Nuclear membrane reforms around the chromosomes
  3. Spindle fibres break down
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9
Q

what is cytokinesis?

A

Cytoplasm and cell-surface membrane divides into two

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10
Q

What does the nucleus do?

A

The nucleus contains DNA wrapped around histone proteins in a complex called chromatin, and a nucleolus, which is the site of ribosome production.

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11
Q

What does rough endoplasmic reticulum do?

A

A series of flattened sacs enclosed by a membrane with ribosomes on the surface. The RER folds and processes proteins made on the ribosomes; often located close to the nucleus.

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12
Q

What does smooth endoplasmic reticulum do?

A

Membrane-bound sacs. The SER produces and processes lipids.

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13
Q

What does the golgi apparatus do?

A

A series of fluid-filled, flattened and curved sacs with vesicles surrounding the edges. The Golgi apparatus modifies and packages proteins (after budding off from the RER) as well as lipids. It also produces lysosomes.

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14
Q

What does the mitochondria do?

A

Oval-shaped and bound by a double membrane called the envelope. The inner membrane is folded to form projections called cristae, with a fluid matrix on the inside containing the enzymes needed for aerobic respiration.

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15
Q

What do centrioles do?

A

Form fibres in cell division known as spindles which separate chromosomes. Small protein tubes of microtubules.

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16
Q

What do 80S ribosomes do?

A

Protein synthesis.

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17
Q

What do lysosomes do?

A

Vesicles, containing hydrolytic digestive enzymes, bound by a single membrane.

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18
Q

What is protein trafficking?

A
  1. Proteins are produced on the ribosomes.
  2. Proteins which are produced on the ribosomes on the surface of RER are folded and processed in the RER.
  3. The proteins are then transported from the RER to the Golgi apparatus in vesicles. Vesicles pinch off from the rough ER and fuse with the Golgi apparatus.
  4. They are then modified (e.g. carbohydrates are added to form a glycoprotein) in the Golgi Apparatus.
  5. The Golgi Apparatus packages proteins into secretory vesicles to be transported around the cells to where they’re required. Some of the proteins, such as extracellular enzymes, leave the cell by exocytosis.
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19
Q

Features of eukaryotic cells e.g. plant and animal cells

A
  • nuclear membrane
  • rough endoplasmic reticulum
  • smooth endoplasmic reticulum
  • golgi apparatus
  • mitochondria
  • centrioles
  • 80S ribosomes
  • lysosomes
  • nucleolus
  • linear DNA
  • reproduce sexually via mitosis and meiosis
  • has membrane bound organelles
  • cell-surface membrane (made of cellulose in plants)
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20
Q

Features of prokaryotic cells e.g. bacteria

A
  • cell wall made of peptidoglycan
  • slime capsule
  • plasmid
  • flagellum
  • pili
  • 70S ribosomes
  • mesosomes
  • circular DNA
  • unicellular
  • no membrane bound organelles
  • can reproduce asexually via binary fission
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21
Q

What does a cell wall do?

A

The cell’s rigid outer covering made of peptidoglycan (murein). Provides the cell with strength and support.

22
Q

What does a slime capsule do?

A

A protective slimy layer which helps the cell retain moisture and adhere to surfaces.

23
Q

What does a plasmid do?

A

Small ring of DNA.

24
Q

What does a flagellum do?

A

A tail-like structure which rotates to move the cell.

25
Q

What does pili do?

A

Hair-like structures which attach to other bacterial cells allowing the exchange of plasmids.

26
Q

what do 70S ribosomes do?

A

Protein synthesis.

27
Q

What do mesosomes do?

A

Infoldings of the inner membrane - believed they contain enzymes required for respiration.

28
Q

Similarities between prokaryotic and eukaryotic cells

A
  • Both have cell membrane
  • Both have cytoplasm
  • Both have ribosomes
  • Both have DNA
29
Q

What does nucleolus do?

A

Dense region in the nucleus consisting of RNA.

30
Q

Adaptations of the ovum

A
  • It contains the zona pellucida which is a protective coating which the sperm have to penetrate in order for fertilisation to occur, it then hardens after they have entered to prevent polyspermy.
  • It contains a haploid nucleus so that a full set of chromosomes is restored at fertilisation.
  • Cortical granules release substances which cause the zona pellucida to harden.
  • Follicle cells form a protective coating around the egg.
31
Q

Adaptations of sperm

A
  • Sperm cells contain many mitochondria to provide energy for rotation of the flagellum which enables the cell to move.
  • Acrosomes contain digestive enzymes which break down the zona pellucida and allow sperm to penetrate the egg.
32
Q

Define locus

A

The location of a gene on a chromosome.

33
Q

Define autosomal linkage

A

Alleles on the same chromosomes and are inherited to a greater extent. The closer the loci of the genes on the chromosome, the more closely linked they are. And less likely to be separated during crossing-over in meiosis.

34
Q

What are sex-linked alleles

A

Alleles that are only on the X chromosomes. Sex-linked disorders are more common in men because they only have one copy of the sex-linked allele on the X chromosome not the Y (too small), so it will always be expressed.

35
Q

Difference between Mitosis and Meiosis

A
  • Mitosis produces 2 genetically identical daughter cells (diploid cells, 2n chromosomes)
  • Meiosis produces 4 genetically different gametes (haploid cells, n chromosomes - reduction division)
36
Q

How does meiosis produce genetic variation

A
  1. Crossing-over - the exchange of alleles between homologous chromosomes / non-sister chromatids (the points of exchange on the chromatids is called chiasma). Produces recombinant chromatids.
  2. Independent assortment - there are various arrangements at the cell’s equator of maternal and paternal chromosomes which are distributed between the haploid cells.
37
Q

How does polysomy occur during meiosis

A

When either homologous chromosomes or sister chromatids fail to separate is called nondisjunction. So there is an extra chromosome than normal.

38
Q

What are stem cells and the types

A

Stem cells are undifferentiated cells which can keep dividing to give rise to other cell types. Embryonic stem cells or adult stem cells (bone marrow)

  1. Multipotent - cells which can give rise to many different types of cells.
  2. Pluripotent - cells which are able to give rise to some types of specialised cells.
  3. Totipotent - cells which can give rise to all / any types of specialised cells.
39
Q

Uses of stem cells and ethics of use

A
  • Treat a variety of diseases: diabetes, multiple sclerosis and Parkinson’s disease.
  • Used to replace damaged tissue like nerve tissue.
  • Unethical as embryos are killed in the process of embryonic stem cell extraction.
  • there’s a risk of infection when cells are transplanted because they are incompatible, and they could become cancerous.
40
Q

How do stem cells become specialised

A

Differential gene expression allows cells to become specialised:

  • A stimulus acts on unspecialised cells.
  • Activator (acetyl group) and repressor (methyl group) molecules can bind to promoter regions on the DNA sequence. Some genes become switched on and are active whereas other genes are switched off, by changing the structure of chromatin, making it more or less open to being freely transcribed.
  • The active genes are transcribed to produce RNA
  • mRNA is then translated by ribosomes and used to produce protein.
  • The protein has the ability to change the structure and function of cells.
41
Q

Define phenotype

A

The characteristics of an organism, which result from the interaction of the genes of the organism with the environment in which it lives.

42
Q

What are the two types of variation in phenotype

A
  1. Continuous variation - is variation within a range and it includes mass and height. Polygenic inheritance (when several genes at different loci determine a characteristic) gives rise to continuous variation.
  2. Discontinuous - can only take particular values such as gender or shoe size. Characteristics influenced by only one gene, known as monogenic, gives rise to discontinuous characteristics.
43
Q

What are epigenetic modifications

A

Epigenetic modifications are modifications to DNA which do not change the base sequence. Epigenetic modifications modify the activation of certain genes.

44
Q

What is mitotic index formula

A

the number of cells undergoing mitosis / total number of cells

45
Q

Define autosome

A

A chromosome that is not a sex chromosome

46
Q

What is somatic nuclear transfer (cloning)

A
  • Used to clone Dolly the sheep
  • Tissue cells from animal to be cloned are maintained in the lab so they do not grow.
  • A donor supplies unfertilised egg.
  • The nucleus is removed from both tissue cells and egg cell.
  • Nucleus from tissue cell fuses with empty egg after electric current is applied.
  • The reconstructed embryo grows for 7 days.
  • Embryo is then implanted into surrogate mother.
  • Cloned animal is born with exact DNA as the tissue cell donor.
47
Q

Explain how lactose regulates gene expression in the lac operon

A
  • The repressor protein binds to the operator region (next to the promoter region)
  • Which blocks the binding of RNA polymerase to the promoter region
  • Therefore, the genes cannot be transcribed, i.e. the genes (operon) are inactivated
  • Lactose (in milk) binds to the repressor protein which changes its shape (conformation)
  • The repressor protein cannot remain bound to the operator region
  • Thus, RNA polymerase is able to bind to the promoter region
  • Allowing the genes to be transcribed, i.e. the genes (operon) are activated
48
Q

What is phototropism

A

Plant response to light stimulus.
Grows towards light - positive phototropism
Grows away from light - negative phototropism

49
Q

How does phototropism work

A
  1. The stem tip is the site of production for auxins.
  2. Transporter proteins in the membrane causes auxins to be actively pumped away from the sunny side and to accumulate in the shaded side.
  3. The auxins diffuses down the shaded side.
  4. Auxins activate transcription factors that leads to genes being activated that leads to cell elongation.
  5. Cell elongation occurs due to acidification and enzymes being produced that break cross-links that hold cellulose together in the cell wall.
  6. The vacuole is then able to increase in size that leads to cell elongation.
  7. Cell elongation occurs on the shaded side, causing the shoot to curve towards the light.
50
Q

What is a operon

A

A cluster of genes with related functions that share a common promotor region

Biology A-level (9 decks)

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