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Biology AS Level > Topic 3 - Voice Of Genome > Flashcards

Topic 3 - Voice Of Genome Flashcards

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1
Q

What is a prokaryotic cell?

A

An organism which has cells that do not contain a nucleus or other organelles surrounded by membranes. Bacteria are prokaryotes. Animals and plants are eukaryotes; their cells have nuclei and membrane-bound organelles such as mitochondria and chloroplasts.

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2
Q

What is a eukaryotic cell?

A

An organism that has cells containing a nucleus. Eukaryotic cells also contain organelles such as chloroplasts and mitochondria, which are surrounded by membranes. Animals and plants are eukaryotes; bacteria are prokaryotes. Prokaryotic cells are very small and do not have nuclei or other membrane- bound organelles.

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3
Q

What does a prokaryotic cell contain?

A

-Infolding of cell surface membrane (site of respiration) -Plasmids (small circles of DNA) -Capsule (Slimy layer on surface for protection and to prevent dehydration) -Pili (thin protein tubes allow bacteria to adhere to surfaces) -Flagellum (hollow cylindrical thread-like structure rotates to move the cell) -Cytoplasm -Cell wall (contains peptidoglycan, a type of polysaccharide and peptide combined) -Cell surface membrane -Circular DNA -Ribosome

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4
Q

Which cell is larger a eukaryotic cell or a prokaryotic cell?

A

A eukaryotic cell is larger than a prokaryotic cell.

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5
Q

What organelles do eukaryotic cells have?

A

-Centrioles -Mitochondrion -Nucleus -Nucleolus -Rough endoplasmic reticulum -Ribosomes -Cell surface membrane -Smooth endoplasmic reticulum -Golgi apparatus -Lysosome

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6
Q

What are centrioles?

A

Every animal has one pair of centrioles, which are two hollow cylinders made up of a ring of nine protein microtubules (polymers of globular proteins arranged in a helix to form a hollow tube). They are arranged at right angles to each other and they are involved in the formation of the spindle during nuclear division and in transport within the cell cytoplasm.

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7
Q

What are mitochondria?

A

They are surrounded by a double membran and the inner membrane is folded into finger-like projections called cristae. The central area contains a jelly called the matrix containing: 70S ribosomes and DNA. Mitochondria are the site of aerobic respiration.

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8
Q

What is a nucleus?

A

Enclosed by an envelope composed of two membranes perforated by pores. Contains chromosomes and a nucleolus. Chromosomes made of DNA contain genes that control the synthesis of proteins.

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9
Q

What is a nucleolus?

A

It is a dark staining area within the nuclear envelope and is a region of dense DNA and protein where ribosomes are made.

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10
Q

What is the rough endoplasmic reticulum?

A

A system of interconnected membrane-bound, flattened sacs enclosed by a membrane. Ribosomes are attached to the outer surface. Proteins made on these ribosomes are transported through the ER to other parts of the cell.

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11
Q

What are ribosomes?

A

Made of RNA and protein, these small organelles are found free in the cytoplasm or attached to the endoplasmic reticulum. They are the site of protein synthesis. In eukaryotes they are 80S whereas in prokaryotes they are 70S.

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12
Q

What is a cell surface membrane?

A

(Also known as the plasma membrane) Phospholipid bilayer containing proteins and other molecules forming a partially permeable barrier.

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13
Q

What is the smooth endoplasmic reticulum?

A

La series of single, tubular sacs made of membrane. They are like rough ER, but does not have any attached ribosomes. Smooth ER makes lipids and steroids (e.g reproductive hormones).

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14
Q

What is the golgi apparatus?

A

A series of single, curvered and flattened sacs enclosed by a membrane. The Golgi apparatus Modifies proteins and packages them in vesicles for transport. Many vesicles cluster around the Golgi apparatus.

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15
Q

What are lysosomes?

A

Spherical sacs contains digestive enzymes and bound by a single membrane. Involved in the breakdown of unwanted structures within the cell (old organelles and pathogens), and in the destruction of whole cells when old cells are to be replaced or during development. The acrosome is a specialised lysosome.

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16
Q

Describe the protein folding, modification and packaging (Protein trafficking)

A

1)Transcription of DNA to mRNA. 2) mRNA leaves the nucleus 3) Amino acids made into proteins on ribosomes enter through the ER. 4) Newly made proteins is stored and folded in the rER cavity. 5) Protein is packed at the end of the rER by vesicles as the membrane closes. 6) Vesicles, pinched off the rER, transport proteins towards the Golgi apparatus. 7) Proteins are modified within the Golgi apparatus. 8) Vesicles pinched off the Golgi apparatus contain the modified protein. 9) Vesicle fuses with cell surface membrane releasing protein, such as extracellular enzymes.

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17
Q

What are the gametes?

A

Sex cells, in mammals the sperm and ovum

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18
Q

How is the ovum adapted for sexual reproduction?

A
  • Haploid nucleus - as in sperm
  • Cytoplasm full of energy rich material (proteins and lipid food reserves for a developing embryo)
  • zona pellucida - to stop more than one sperm fertilising the egg
  • special vesicles (cortical granules) - these contain a substance that help stop more than one sperm fertilising the egg
  • large cell incapable of independent movement
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19
Q

How is the sperm adapted to sexual reproduction?

A
  • Flagellum for movement to swim to egg
  • Mid region with mitochondria to provide the energy (from respiration) for movement
  • Acrosome containing enzymes to digest the outer layers of the egg
  • Haploid nucleus contains the haploid number chromosomes so that full complement restored at fertilisation.
  • Smaller than the ovum and is motile (can move).
  • Males continuously produce large numbers of sperm once they have reached maturity.
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20
Q

Describe the process of fertilisation.

A

Sperm that enter the vagina during intercourse swim through the uterus, their passage assisted by the muscular contractions of the uterus walls. If intercourse takes place at about the time of ovulation, sperm may meet the ovum in the oviduct. The sperm are attracted to the ovum by chemicals released from it, triggering the acrosome reaction. When the front of the sperm touches the zona pellucida of the egg the acrosome bursts and releases enzymes which digest a channel through the zona pellucida and the follicle cells. Membrane fusion then occurs where the surface membranes of the sperm and the egg fuse allowing the haploid nucleus from the sperm to enter the cytoplasm of the egg. The cortical reaction then follows which is where vesicles inside the egg called cortical granules fuse with the cell membrane and release their contents. These cause changes in the surface layer of the egg preventing other sperm from entering. The presence of the sperm causes the 2nd division and meiosis takes place. Finally, the chromosomes from the haploid sperm and those from the haploid egg combine to restore the diploid number; this is fertilisation.

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21
Q

What is the acrosome?

A

An organelle in the head of a sperm that contains digestive enzymes.

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22
Q

Describe the acrosome reaction

A

When fertilisation takes place, the membrane surrounding these enzymes bursts. The enzymes digest the follicle cells; they also digest the jelly- like layer surrounding the egg cell allowing the sperm to fuse with the egg membrane.

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23
Q

Name the different parts of the ovum

A

-cytoplasm -haploid nucleus -lysosomes -follicle cells from ovary -jelly-like coating (zona pellucida) -lipid droplets -Cell surface membrane

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24
Q

Name the different parts of the sperm

A

-Acrosome (head) -Nucleus (head) -Mitochondria (middle) -Flagellum

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25
Q

Human cells contain how many chromosomes?

A

46 chromosomes made up of 22 homologous pairs and one pair of sex chromosomes.

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26
Q

What is the main difference between gametes and normal cells?

A

Gametes contain half the amount of chromosomes found in other body cells.

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27
Q

What special name is given to gametes as they only have the half amount of chromosomes?

A

Haploid

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28
Q

Why are gametes haploid?

A

If sperm and ovum cells both had the full chromosome number, which is 46 in humans, the zygote would have 92 chromosomes. When this individual reproduced the zygote would contain 184 chromosomes. With each generation the number of chromosomes would double, which obviously would not work. This is why the gametes are haploid containing half the full number of chromosomes -23 in humans- made up of one of each homologous pair and one sex chromosome. When the gametes fuse,the full number of 46 is restored. Ad upload zygote is formed.

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29
Q

What is mitosis?

A

The process by which the cell nucleus divides to give two new nuclei. Each of these new nuclei has the same number of chromosomes as the original nucleus. Mitosis is a continuous process but it is conveniently divided into four stages: prophase, metaphase, anaphase and telophase.

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30
Q

What is meiosis?

A

A type of nuclear division that produces gametes or sex cells in animals and plants. Meiosis produces haploid cells, each of which contains half the number of chromosomes found in a body cell, one chromosome from each homologous pair.

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31
Q

What is a haploid?

A

Cells or organisms in which the nuclei contain one copy of each chromosome. The gametes produced by animals and plants are haploid. In humans, 46 chromosomes are found in each body cell. This is the diploid number. Gametes are formed by a type of cell division called meiosis. This results in gametes which have 23 chromosomes so 23 is the human haploid number. This may be written as n=23.

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32
Q

What is a diploid?

A

Cells or organisms in which the nuclei contain two copies of each chromosome. The diploid number of chromosomes differs from one species to another. In humans, the diploid number of chromosomes is 46. This is sometimes written as 2n=46.

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33
Q

What does mitosis produce?

A

It produces new body cells as an organism grows and develops.

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34
Q

What does meiosis produce?

A

Gametes with only half the number of chromosomes.

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35
Q

What are the two important roles of meiosis?

A

-It results in haploid cells, which are necessary to maintain the diploid number after fertilisation -It helps create genetic variation among offspring.

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36
Q

Describe the gamete production by meiosis

A

A cell with 4 chromosomes in 2 pairs. The homologous chromosomes pair with each other in the middle of the cell. The homologous chromosomes are pulled apart. The first division results with two cells with a pair of chromosomes. The two products of meiosis 1 divide again (chromatids separate) to give 4 cells which become gametes (sex cells).

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37
Q

Describe independent assortment

A

The arrangement of each chromosome pair during the first division of meiosis is completely random. An organism with chromosomes, that is three homologous pairs XX,YY,ZZ could form 8 (2 to the power of 3) combinations in its gametes.

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38
Q

How does independent assortment guarantee the individuals to be different?

A

When these daughter cells join with another set at fertilisation, this pretty well guarantees that individuals produced from sexual reproduction are genetically different from each other. In organisms with many chromosomes, such as humans with 23 pairs, the number of possible combinations is so large that it is unlikely any two daughter cells will have the same chromosome combinations.

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39
Q

What is crossing over?

A

During the first meiotic division, homologous chromosomes come together as pairs and all four chromatids come into contact. At these contact points the chromatids break and rejoin, exchanging sections of DNA between non-sister chromatids. The point where the chromatids break is called a chiasma and several of these often occur along the length of each pair of chromosomes, to give rise to a large amount of variation.

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40
Q

What does crossing over produce?

A

Crossing over produces chromosomes that contain new combinations of alleles from both parents.

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41
Q

What is sex linkage?

A

When a gene is carried on a sex chromosome, it is said to be sex-linked. In most animals, the Y chromosome contains very few genes. Sex-linked genes, like those that produce tortoiseshell cats, are therefore most likely to be found on the X chromosome.

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42
Q

What is the linkage of genes?

A

Any two genes with a locus on the same chromosome are linked together and will tend to be passed as a pair to the same gamete.

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43
Q

What does a longer gene have?

A

They have more genes in the chain.

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44
Q

How are chromosomes ordered?

A

Longest to shortest. Therefore we expect chromosome 1 to contain the genes and chromosome 22 to contain the least.

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45
Q

What is the sex chromosome?

A

One of the chromosomes which determines the sex of an organism. In humans and other mammals, the female has two X chromosomes in each of her body cells. A male has one X chromosome and one Y chromosome. The X and Y chromosomes are the sex chromosomes.

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46
Q

Regarding the sex chromosome, what are males?

A

XY

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47
Q

Regarding the sex chromosome, what are females?

A

XX

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48
Q

Give an example of a sex linked condition?

A

Colourblindness which is more common in men than women.

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49
Q

What is fertilisation?

A

The process in which a male gamete fuses with a female gamete to form a zygote.

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50
Q

What is the cell cycle?

A

The well-organised pattern of events in which a cell that has just resulted from a cell division eventually itself divides to form new cells.

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51
Q

What are the three parts of the cell cycle (in order)?

A

G1, S, G2

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52
Q

What is interphase?

A

As an organism grows, its cells make new contents and then divide. The resulting pattern of growth and mitosis is called the cell cycle. Interphase is the stage in the cell cycle between mitotic divisions when the cell synthesises new cell components, such as organelles and membranes and DNA replication takes place. At the end of interphase, the cell enters mitosis and starts to divide again.

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53
Q

In the cell cycle what does the S stand for?

A

Synthesis of DNA

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54
Q

In the cell cycle what separates the G1 phase and the G2 phase

A

The S phase

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55
Q

What does the length of the interface depend on?

A

The role of the cell

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56
Q

Which phases of the cell cycle remain relatively constant in duration?

A

S and G2 phase whereas the length of the G1 phase is more variable: some cells can take weeks, months or even years to complete this phase.

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57
Q

Give two examples of cells within the human body that never divide again and remain in a non-dividing state

A

Nerve and muscle cells

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58
Q

What are ribosomes made of?

A

Protein and rRNA (ribosomal RNA)

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59
Q

Describe what happens during interphase

A

The individual chromosomes are unravelled. This allows access to the genetic material, enabling new proteins to be synthesised.

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60
Q

What happens in preparation for cell division?

A

In preparation for cell division, the cell synthesises additional cytoplasmic proteins and organelles. The cell must also produce copies of DNA for the two new cells. It is vital that this DNA is identical in both structure and quantity to the DNA for the two new cells.

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61
Q

What follows interphase?

A

Nuclear division

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62
Q

What is nuclear division?

A

The DNA and the contents of the cytoplasm are separated in nuclear division (mitosis).

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63
Q

What is cytoplasmic division?

A

The stage after the end of mitosis in which the cytoplasm divides into two, allowing the two new nuclei to belong to distinct cells.

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64
Q

What follows nuclear division in the cell cycle?

A

Cytoplasmic division

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65
Q

What are the four stages of mitosis?

A

-Prophase -Metaphase -Anaphase -Telophase

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66
Q

By the end of interphase what is the cell able to do?

A

It contains enough cell content to produce two new cells.

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67
Q

What is the order of the cell cycle with all the individual stages?

A

Interphase Prophase Metaphase Anaphase Telophase Cytoplasmic division

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68
Q

Describe what happens during prophase.

A

During prophase, the chromosomes condense, becoming shorter and thicker, with each chromosome visible as two strands called chromatids. Apart from the occasional mutation, the two strands are identical copies of one another, produced by replication. They are effectively two chromosomes joined at one region called the centromere. During prophase, microtubules from the cytoplasm form 3D structure called the spindle. The centrioles move around the nuclear envelope and position themselves at opposite sides of the cell. These form the two poles of the spindle and are involved in the organisation of the spindle fibres. The spindle fibres form between the poles. The widest part of the spindle is called the equator.

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69
Q

Describe what happens during metaphase.

A

The chromosomes’ centromeres attach to spindle fibres at the equator. When this has been completed the cell has reached the end of metaphase.

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70
Q

Describe what happens during anaphase.

A

The centromeres split. The spindle fibres shorten, pulling the two halves of each centromeres in opposite directions. One chromatid of each chromosome is pulled to each of the poles. Anaphase ends when the separated chromatids reach the poles and the spindle breaks down.

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71
Q

Describe what happens during telophase.

A

This is effectively the reverse of prophase. The chromosomes unravel and the nuclear envelope reforms, so the two sets of genetic information become enclosed in separate nuclei.

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72
Q

Describe what happens during cytoplasmic division.

A

After nuclear division, the final reorganisation into two new cells occurs.

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73
Q

Describe cytoplasmic division within animals.

A

In animal cells, the cell surface membrane constricts around the centre of the cell. A ring of protein filaments bound to the inside surface of the cell surface membrane is thought to contract until the cell is divided into two new cells. It has been proposed that proteins actin and myosin, responsible for muscle contractions, may also be the proteins for cytoplasmic division.

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74
Q

Describe cytoplasmic division within plants.

A

Plant cells synthesise a new plate cell between the two new cells.

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75
Q

What stage of the mitosis is this?

A

Prophase

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76
Q

What stage of mitosis is this?

A

Metaphase

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77
Q

What stage of mitosis is this?

A

Late anaphase

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78
Q

What stage of mitosis is this?

A

Telophase

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79
Q

What stage of mitosis is this?

A

Cytoplasmic division

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80
Q

What stage of mitosis is this?

A

Interphase

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81
Q

Why do chromosomes condense?

A

Condensing allows the DNA molecules to move around the cell without getting tangled up.

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82
Q

Why does the nuclear envelope disintegrate?

A

The pores in the nuclear envelope are not large enough for whole molecules of DNA to pass through; once it disintegrates the chromosomes can move freely through the cell.

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83
Q

What does mitosis ensure?

A

Genetic consistency, with daughter cells genetically identical to each other and to the parent cell.

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84
Q

As a aresult of mitosis, each daughter cell contains exactly the same number and type of chromosomes as their parent cell. How is this achieved?

A
  • DNA replication prior to nuclear division
  • the arrangement of chromosomes on the spindle and the separation of chromatids to the poles.
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85
Q

What is mitosis important for?

A

Growth and repair and assexual reproduction

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86
Q

Starfish can re-grow damaged parts of their body, how?

A

Some organisms, including starfish, can regenerate lost or damaged body parts using mitosis.

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87
Q

What is it called when organisms reproduce without producing gametes?

A

Asexual reproduction

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88
Q

Describe asexual reproduction

A

Organisms grow copies of themselves by mitosis, producing offspring that are genetically identical to each other and to their parent.

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89
Q

What is unusual about mosses, liverworts and many flowering plants?

A

They reproduce asexually at one stage in their life cycle and sexually at another.

90
Q

How do prokaryotes divide?

A

Thye do not carry out mitosis or meiosis because they do not possess chromosomes. However they do carry out binary fission, one cell splits into two identical cells.

91
Q

What is a centromere?

A

The region on a chromosome where two chromatids are held together during the early stages of cell division. The centromere is also the region to which the spindle fibres attach. The spindle fibres pull the chromatids apart during anaphase.

92
Q

What are chromatids?

A

One of the two strands of genetic material that make up a chromosome. When chromosomes become apparent at the beginning of mitosis, each can be seen to consist of two strands of genetic material. Each of these strands is called a chromatid. During mitosis these chromatids and pulled apart and go to the opposite poles of the cell.

93
Q

What are spindles?

A

A structure formed from protein tubules in the cytoplasm during cell division. The spindle fibres attach to the centromeres of the chromosomes and shorten. As they shorten they pull the two halves of the centromere apart. In mitosis the centromeres split and, as a result, one chromatid of each chromosome is pulled to each of the poles of the dividing cell. The spindle plays a similar part during meiosis.

94
Q

What are totipotent cells?

A

Totipotent Totipotent cells can give rise to any type of specialised cell. We all started life as a single cell or zygote. This zygote divides by mitosis. After it has undergone three mitotic divisions there will be eight cells present. Each of these totipotent embryonic stem cells can give rise to any of the specialised cells which make up the adult human body.

95
Q

By five days after conception what happens?

A

A hollow balls of cells called the blastocyst has formed.

96
Q

What does the outer blastocyst cell layer go on to form?

A

The placenta

97
Q

What does the inner cell mass (inside the blastocyst) go onto form?

A

This goes on to form the tissue of the developing embryo.

98
Q

The inner cell mass (inside the blastocyst), what are these cells known as?

A

Pluripotent embroyonic stem cells

99
Q

What is the blastocyst?

A

When a zygote develops into an embryo, it first divides to form a hollow ball of cells. This hollow ball of cells is called a blastocyst.

100
Q

What is the placenta?

A

In a mammal, the placenta is an organ formed partly from the tissue of the fetus and partly from the lining of the uterus. The mother’s blood exchanges with the fetus’ blood without the two actually coming in contact with each other. Oxygen and nutrients enter the fetal blood, and carbon dioxide and waste products are removed into the mother’s blood. The placenta also produces a number of hormones that are important in controlling the events of pregnancy. Once a baby has been born, the placenta forms part of the ‘afterbirth’.

101
Q

What are pluripotent embryonic stem cells?

A

Pluripotent cells are able to give rise to many types of specialised cell (216 cells that make a human adult). The cells that make up the inner mass of a blastocyst are known as pluripotent embryonic stem cells.

102
Q

What does differeientiated mean?

A

We all started life as an undifferentiated single cell or zygote. As we grew and developed into adults, our cells became specialised for different purposes. The process by which cells become specialised is called differentiation. When plants are produced by micropropagation, unspecialised cells differentiate to form the many types of cell in an adult plant.

103
Q

What are multipotent stem cells?

A

Multipotent stem cells have the ability to develop into more than one cell type, but are more limited than pluripotent stem cells. In adults, some cells still have the ability to differentiate and give rise to a variety of cell types. These cells are called multipotent stem cells. Multipotent stem cells in bone marrow develop into different sorts of blood cell.

104
Q

Give an example of an adult stem cell

A
  • Nerve stem cells
  • Blood stem cells
105
Q

Regarding differentiated and undifferentiated cells what is the difference between animals and plants?

A

Many plant cells remain totipotent throughout the life of the plant. Cell differentiation is irreversible in animals, but many differentiated plant cells can de-differentiate and then develop into a complete new plant.

106
Q

What is the benefit to humans regarding the totipotency of plant cells?

A

Totipotency of plant cells allows plants to be reproduced using plant tissue culture.

107
Q

How do we reproduce plants using plant tissue culture?

A

Small peices of a plant, known as explants, are surface sterilised and then placed on a solid agar medium with nutrients and growth regulators. The cells divide to form a mass of undifferentiated cells known as a callus. By altering the growth regulators in the medium, cells of the callus can be made to differentiate to form small groups of cells that are very similar to plant embryos. These embryos develop into complete plants that are genetically indentical clones.

108
Q

What is the importance of plant tissue culture?

A

Plant tissue culture allows commercial growers to produce large numbers of genetically identical plants rapidly. Tissue culture is important in plant biology research, plant breeding, genetic modification of plants and in the conservation of endangered plants.

109
Q

Why could embryonic stem cells be used in medicine?

A

Embryonic stem cells may be the most sutible for of treatment for regenerative medicine because of their potential to develop into any cell type which offers the greates flexibility for development (unlike adult stem cells).

110
Q

What is the source of embryonic stem cells?

A

These are produced in fertility clinics that carry out in vitro fertilisation, where the ovum is fertilised outside the body. Women undergoing this treatment are given drugs to make them superovulate, producing more eggs than are needed for infertility treatment. Many of the embryos end up being placed in women’s wombs in hope of enabling infertile couples to have children, but any additional embryos could be a source of embryonic stem cells.

111
Q

What do some people with their extra embryos?

A

Some people donate for research purposes.

112
Q

What do scientists do with the embryos in the laboratory?

A

Embryos being used for research are allowed to grow to form balstocysts. At this point, the embryos are cultured for a further period of time to see if stem cells are formed. The stem cells are isolated from each embryo and the rest of the embryo (which could not develop further) is discarded. The stem cells are then cultured and used in research.

113
Q

What is one problem that might occur if scientists manage to grow the right tissue?

A

The tissue might end up being rejected by the immune system of the person given the transplant.

114
Q

One issue that might occur with grown tissue is that it might be rejected by the person given the transplant. How might the scientists be able to solve this problem?

A

it might be possible to get around the problem of rejection by using drugs that prevent the recipient from rejecting any transplanted organ or by using tissue-typing.

115
Q

What is therapeutic cloning?

A

Research procedure in which it is hoped that a diploid cell could be induced to develop so as to form a tissue or organ needed for a transplant.

116
Q

What is the process of somatic cell nuclear transfer?

A

A diploid cell is removed - this could simply be a cell from the base of a hair or any other sutible tissue. This cell, or its nucleus, would then be fused with an ovum from which the haploid nucleus had been removed. The result would be a diploid cell rather like a zygote.

117
Q

When is the process of somatic cell nuclear transfer used?

A

It is used for therapeutic cloning

118
Q

In therapeutic cloning once somatic cell nuclear transfer has occured, what happens? What does the procedure result in ?

A

The cell can then be stimulated to divide by mitosis. If all goes to plan, after about five days a blastocyst would develop. Stem cells could then be isolated from this and encouraged to develop into tissue. This procedure results in cell lines, and perhaps eventually organs for transplantation, which are genetically identical to the patient from whom the original diploid cell was taken.

119
Q

How are animal eggs used to form stem cells?

A

The nucleus of the animal egg is removed and a human nucleus is fused with the egg cell: the resulting cloned embryos are a source of stem cells for research.

120
Q

Why are scientists researching adult stem cells?

A

Many people have ethical objections to the use of embryonic stem cells and advocate the use of adult stem cells.

121
Q

Adult stem cells have been injected into different areas of the body for trying to heal a range of degenerative conditions. How else have they been used?

A

Adult stem cells have also been used to produce cells for transplantation. For example, to treat patients with burns.

122
Q

What is the benefit of iPSCs?

A

The use of these would overcome the problems of cell rejection and address ethical concerns with the use of embryonic stem cells.

123
Q

Working on animal models, what diseases have iPSCs managed to treat?

A

Sickle cell anaemia, Parkinson’s disease, haemophilia and ischaemic heart disease.

124
Q

What is the discussion about the use of iPSCs?

A

It remains unclear whether iPSCs could eventually replace embryonic stem cells in research and furture treatments.

125
Q

What are ethical issues regarding the use of embryonic stem cells?

A
  • Embryos are potential humans and have a right to life.
  • Women having IVF may be pressured into producing surplus embryos.
126
Q

Who decides whether embryonic stem cells can be used?

A

Decisions are made by:

  • People working in the stem-cell field, who understand the issues and what is possible
  • everyone else, because they can give a range of alternative points of view
127
Q

UK law only allowed the use of human embryos where the HFEA considered their use to be necessary or desirable. When can they be used?

A
  • To promote advances in the treatment of infertility
  • To increase knowledge about the causes of congenital diseases
  • To increase knowledge about the cause of miscarriage
  • To develop more effective methods of contraception
  • To develop methods for detecting gene or chromosome abnormalities in embryos before implantation
128
Q

Describe the experiment that concluded that the nucleus controls the whole multicellular organism’s phenotype?

A

This experiment used giant algal cells and was completed in 1934 by a Danish biologist. He used a Acetabularia mediterranea and a Acetabularia crenulata which are two forms of giant algal cells. The biologist removed the hats and swapped the stalks between the two cells. The plants then developed hats with features of both species. If the intermediate hats are removed, new ones grow that correspond to the nucleus in the rhizoid. This demonstrates the role of the nucleus and chemical messengers in the development of the cell.

129
Q

Describe the process of cloning in animals

A

You need two animals of the same species e.g. 2 sheep. A mammary cell donor sheep and an egg cell donor sheep. The mammary cells are grown in culture and egg cells are removed from the ovary. The egg cell has its nucleus removed and the nucleus from the mammary cells is fused into the egg cell without the nucleus. Therefore you have the nucleus form the mammary cell inside the egg cell without its nucleus. This is then grown in culture so that it multiplies forming an embryo. This is then implanted into the uterus of a third sheep who is a surrogate mother. The embryo develops within the surrogate mother and a sheep chromosomally identical to the mammary cell donor forms.

130
Q

What is the structure and function of each cell dependent on?

A

The proteins that is synthesises.

131
Q

As an embryo develops, what happens?

A

Cells differentiate: they become specialised for one function or a group of functions.

132
Q

How is it that specialised cells with the full genome of reproduce specific proteins?

A

Different specialised cells must only be expressing some of their genes.

133
Q

How did Igor David and Thomas Sargent demonstrate that different genes are expressed in different cell?

A

They extracted messenger RNA (mRNA) from undifferentiated and differentiated frog cells. Complementary DNA (cDNA) strands were produced for all the mRNA in the differentiated using an enzyme called reverse transcriptase, which as its name suggests, reverses transcription making DNA from mRNA. These cDNA strands were mixed with the mRNA from the undifferentiated cell. Complementary strands of cDNA and mRNA combined to produce double strands of hybrids. When these hybrids, were separated out, there remained a range of cDNA strands that had not been hybridised: the two cells were expressing some of the same genes, but also some different ones.

134
Q

Why do cells become specialised?

A

Cells become specialised because only some genes are switched on and produce active mRNA that is translated into proteins within the cell.

135
Q

What is the epigenome?

A

The epigenome influences which genes can be transcribed in a particular cell. The epigenome should not be confused with the genome.

136
Q

What is the genome?

A

All the DNA containing a full set of genes.

137
Q

What makes up the epigenome?

A

DNA is wrapped around by histone proteins and both the DNA and histones have chemical markers attached to their surface which make up the epigenome.

138
Q

How is a gene switched off?

A

DNA methylation involves the attaching of a methyl group, to cytosine that is next to guanine, as an epigentic marker. The methylation stops the transcription of mRNA by preventing the binding of RNA polymerase. Histones are modified by the addition of acetyl or methyl groups. This causes the DNA to be wrapped up tightly which switches genes off.

139
Q

What are histone proteins?

A

Chromosomes contain proteins as well as DNA. The most abundant of these proteins are the histones. Histones help to package DNA, which is wound tightly round them. Prokaryotic cells such as bacteria do not contain histones.

140
Q

What are two ways genes become switched off?

A
  • DNA methylation
  • Histone modification
141
Q

What is DNA methylation?

A

Methyl group attaches to DNA which prevents transcription, by stopping the RNA polymerase from binding.

142
Q

What is histone modification?

A

The binding of epigenetic markers (methyl or acetyl groups) to histone tails alters how tightly DNA winds around his tone proteins.

143
Q

Regarding whether genes are active or not, what are cells of a particular tissue like?

A

In cells of a particular type of tissue, such as the pancreas, all the genes for the pancreas are active (for instance, the gene for making the enzyme trypsin), but all the genes specific to other tissue, such as the liver and the kidneys, are switched off.

144
Q

What is the model called that shows the switching on of one gene?

A

The lac operan model

145
Q

The French scientists that proposed their theory of gene expression, used which prokaryote?

A

Escherichia coli

146
Q

The prokaryote of Escherichia Coli produces …. and breaks down ……

A

The bacteria only produce the enzyme B-galactosidase to break down the carbohydrate lactose.

147
Q

Lactose is broken down by the enzyme B-galactosidase produced by the prokaryote Escherichia coli. What is lactose broken down into?

A

The enzyme converts the disaccharide lactose to the monosaccharides glucose and galactose.

148
Q

Describe the lac operon model and how the presence or absence of lactose causing a gene to be turned off.

A

When lactose is not present in the environment, the lactose repressor molecule binds to the DNA and prevents transcription of the B-galactosidase gene. It prevents the transcription as due to the repressor moleule binding onto the gene the RNA polymerase cannot bind to the DNA promotor region. If lactose is present in the environment it binds to the repressor, the repressor molecule is prevented from binding to the DNA and the B-galactosidase gene is expressed. mRNA coding for B-galactosidase is transcribed, and translation of this mRNA produces the enzyme.

149
Q

What switches transcription of an individual gene on or off in eukaryotes?

A

Genes in uncoiled, accessible regions of the eukaryotes DNA can be transcribed into mRNA. The enzyme RNA polymerase binds to a section of the DNA adjacent to the gene being transcribed. This section is known as the promoter region. Only when the enzyme has attached to the DNA will transcription proceed. The gene remains switched off until the enzyme attaches to the promoter region successfully. The attachment of a regulator protein is usually also required to start transcription.

150
Q

In eukaryotes how can transcription of a gene be prevented?

A

Transcription of a gene can be prevented by protein repressor molecules attaching to the DNA of the promoter region, blocking the attachment site. In addition, protein repressor molecules can attach to the regulator proteins themselves, preventing them from attaching.

151
Q

What is an example of when gene expression goes wrong?

A

FOP which is characterised by the growth of bones in odd places, such as within muscle and connective tissue. By early adulthood, the abnormal bone growth often leds to freezing of all major joint of the backbone and limbs so they cannot move.

152
Q

What are adhesion molecules? Where are they found? How do they work?

A

Cells have specific recognition molecules, known as adhesion molecules, on their cells surface membrane. Adhesion molecules help to recognise other cells like themselves and stick to them. A small part of each recognition protein is embedded in the cell surface membrane; a larger part extends from the membrane. This exposed section binds to complementary proteins on the adjacent cell. The particular recognition proteins synthesised by a cell determine which cells it can and cannot attach to. If cells from different tissue are separated and mix together, they reform into tissue as the recognition protein binds.

153
Q

Summarise the levels of organisation within organisms

A
  • Cells
  • Tissue
  • Organ
  • Organ system
154
Q

What is a cell?

A

In multicellular organisms, cells are specialised for a particular function.

155
Q

What is tissue?

A

A group of specialised cells working together to carry out one function.

156
Q

What is an organ?

A

A group of tissues working together to carry out one function.

157
Q

What is an organ system?

A

A group of organs working together to carry out a particular function.

158
Q

What is a marker gene?

A

When organisms are genetically modified, new genes are introduced into their cells. To label cells that contain a new gene, a marker gene is also inserted. The marker gene may produce resistance to an antibiotic. Incubating the cells with the antibiotic kills cells which have not taken up the resistance gene along with the other new gene. The use of marker genes is an effective way of finding those cells that have taken up the new gene.

159
Q

What are master genes?

A

a single gene whose expression is both necessary and sufficient to trigger activation of many other genes in a coordinated fashion, leading to the development of a specific tissue or organ.

160
Q

What are the differences in phenotype between members of a population caused by?

A
  • Genetic make up (genotype)
  • The environment in which an individual develops.
161
Q

What is the phenotype?

A

(Outward expression of the genes)The characteristics of an organism, which result from the genes the organism possesses and the environment in which it lives.

162
Q

What is the genotype?

A

The genotype describes an organism in terms of the alleles it contains.

163
Q

Some characteristics are controlled almost completely by the organism’s genotype, with the environment having little or no effect. Give an example

A

Blood type is controlled by the genes they inherit.

164
Q

What is discontinuous variation?

A

Variation in which individuals fall into distinct categories. In peas, for example, plants are either tall or short. There are no intermediates. Discontinuous variation results from the genes that an organism inherits. Environment has little or no effect.

165
Q

Characteristics that lead to discontinuous variation are controlled by genes at at … and are ….

A

Single locus and are often not affected by the environment.

166
Q

What leads to continuous variation of characteristics?

A

Characteristics that are affected by both genotype and environment often show continuous variation.

167
Q

Give an example of a characteristic that is continuous?

A

Human height

168
Q

What is continuous variation?

A

Variation in which there is a complete range from one extreme to the other. Human height is an example of continuous variation. A person can be any height within the human range.

169
Q

Characteristics controlled by genes at many loci will lead to … variation?

A

continous

170
Q

What does polygenic mean?

A

Polygenetic inheritance is when two or more genes are involved in the inheritance of a characteristic.

171
Q

What are multifactorial conditions?

A

Conditions where several genetic factors and one or more environmental factors are involved.

172
Q

Two people inherit the same susceptibility. Do they both develop the illness?

A

No, it will depend on the environmental factor such as their diet, exposure to toxins and stress.

173
Q

What is melanin?

A

A dark pigment found in the skin, hair and eyes. It is made in special cells called melanocytes. Production of melanin is increased by ultraviolet light. This is why sunlight results in the skin becoming darker in colour. Melanin protects the DNA of cells from the harmful effects of ultraviolet light.

174
Q

What are melanocytes?

A

Cells found mainly in the skin, which are responsible for making the dark pigment, melanin. These cells are activated by a hormone called melanocyte-stimulating hormone (MSH). Ultraviolet light increases the amount of MSH, which in turn, causes melanocytes to produce more melanin.

175
Q

What is the melanocytes-stimulating hormone (MSH)?

A

A hormone which activates special skin cells called melanocytes and causes them to make more of the dark pigment, melanin. Ultraviolet light increases the amount of MSH produced. This leads to more melanin being made and the skin becoming darker in colour.

176
Q

What are melanosomes?

A

They are an organelle found in skin cells. Melanosomes contain the pigment melanin.

177
Q

Melanin is made in specialised cells called?

A

melanocytes

178
Q

Where are melanocytes found?

A

They are found in the skin and at the root of the hair in the follicle.

179
Q

What is on the surface of melanocytes cells?

A

MSH receptors

180
Q

What do the melanocytes do?

A

The melanocytes place melanin into organelles called melanosomes.

181
Q

Where do the melanosomes go within the organelle and what is their importance?

A

The melanosomes are transferred to nearby skin and hair cells where they collect around the nucleus, protecting the DNA from harmful UV light.

182
Q

What increases the amount of MSH?

A

Ultraviolet light

183
Q

Describe what happens when there is an increased exposure to UV light.

A

More MSH is produced and more MSH receptors form on the melanocytes. More melanin is produced which means that more melanosomes collect around the nucleus of the skin cell and give more protection.

184
Q

What enzyme do animals use to make melanin?

A

Tyrosinase

185
Q

What environmental factors can influence the epigenome?

A
  • Medicine
  • Drugs
  • Diet
  • Behaviour
186
Q

Give an example of how the environment effects the epigenome

A

Two mice are genetically identical yet are epigentically different. The agouti gene in the normal healthy brown mouse is methylated and so is not expressed. In the yellow, obese mouse the same gene is not methylated and therefore is expressed. The agouti protein binds to the MSH receptors in the skin and prevents the production of the dark pigment. Therefore the diets of these mice is different and has led to genetically identical mice having different epigenetics as the yellow mouse received a diet with a lower amount of methyl.

187
Q

Give an example of how behaviour has changed the epigentics.

A

Researchers divided rat mothers into two groups, consisting of high licking and grooming mothers and low licking and grooming mothers. The rats grew up to be very similar to their mothers. This suggested a genetic difference between the two groups of rats. The scientists then swapped newborn rat pups from each group. The offspring of the high ‘good’ LG mothers brought up by low LG ‘bad’ mothers grew up to be anxious adults. The offspring of the bad mothers brought up by good mothers were calm adults.

188
Q

How can the observations of the character change in the rats be explained?

A

It has been found that the two types of pup are epigenetically different, the GR gene in pups with low grooming and licking have been switched off due to methylation of the gene. This gene produces a receptor protein that binds to the stress hormone glucocorticoid. When enough has bound, it stops the stress response by causing calming signals to be sent out, relaxing the pup after stress. The methylation remains throughout the rat’s life and means the adult rats are calmer and more likely to lick and groom their offspring. If there are low levels of the GR protein, hormone levels remain higher in the blood and the pup or adult rat is stressed for longer.

189
Q

When do cancers occur?

A

Cancers occur when the rate of cell multiplication is faster than the rate of cell death. This causes the growth a tumour, often in tissue with a high rate of mitosis, such as the lungs, bowel, gut or bone marrow. Cancers are caused by damage to DNA.

190
Q

How can DNA be damaged?

A

DNA is easily damaged by physical factors such as UV light or asbestos. The DNA can also be damaged by chemicals, known as carcinogens, which may be in the environment or can be produced by cell metabolism. If DNA is copied incorrectly in gamete formation, an inherited form of cancer can result.

191
Q

How can epigenetic changes to the DNA and histones have a significant role in the development of cancer?

A

Abnormal methylation of genes in cancer cells can lead to activation or deactivation of genes that are controlled in the control of the cycle.

192
Q

Explain why cancers are more likely to occur in tissues with a high rate of mitosis?

A

Each time DNA replicates before mitosis, a few errors will be made (mutations); the higher the rate of mitosis the more likely it is that mutations will occur in genes controlling cell activity, which can result in cancer.

193
Q

Explain why damage to the DNA in an embryo can result in inherited cancer?

A

When the embryo grows into an adult, by mitosis, the cells giving rise to the ovaries or testes may have the DNA error; thus gametes with faulty DNA could form, the cancer-causing error could be passed on in these gametes to the next generation.

194
Q

How does the next stage of the cell cycle begin?

A

During each stage of the cell cycle, proteins are produced that stimulate the next stage in the cycle. Cells also produce proteins that stop the cell cycle, preventing the progress from one stage to the next. These proteins activate or inhibit enzymes that initiate the reactions in the next stage of the cycle.

195
Q

What are the two types of genes that have a role in control of the cell cycle and play a part in triggering cancer. These are:

A
  • Oncogenes
  • Tumour suppressor genes
196
Q

What is an oncogene?

A

A gene that codes for a protein that stimulates the cell cycle. Mutations in these genes can lead to the cell cycle being continually active, causing excessive cell division. This may result in cancer.

197
Q

What is a tumour suppressor gene?

A

Tumour suppressor genes are genes that code for proteins that stop the cell cycle at appropriate checkpoints. Mutations may affect these genes and stop them from working. If this happens, the cell loses control of the cell cycle. A tumour may result and the person may develop cancer.

198
Q

Explain how less methylation of the oncogenes could contribute to the development of cancer.

A

Less methylation of the oncogenes would mean increased transcription of the proteins that stimulate the transition between stages in the cell cycle, making the cycle more active with increased cell division.

199
Q

Explain how more methylation of the tumour suppressor genes could contribute to the development of cancer.

A

More methylation of the tumour suppressor genes would prevent transcription of the proteins that stop the cell cycle moving from one stage to the next, leading to increased cell division.

200
Q

Why is cancer more likely in older people?

A

Cancers are more likely in older people as they have accumulated more mutations.

201
Q

Can cancers be inherited?

A

Yes, most common cancers occur more frequently in close relatives of cancer patients, suggesting an inherited component.

202
Q

What is the greatest environmental risk to cancer?

A

Smoking

203
Q

How does smoking lead to cancer?

A

Smoking increases the likelihood of many forms of cancer, especially lung cancer, through the action of carcinogens in tar. Tar lodges in the bronchi and causes damage to DNA in the surrounding epithelial cells.

204
Q

How can your diet lead to cancer?

A

You have an increased chance of cancer if you eat a low amount of fruit and vegetables as they contain antioxidants that destroy radicals. Radicals contribute to ageing and cancer through DNA damage.

205
Q

What are the two types of stem cells?

A

Adult

Embryonic

206
Q

What are the pili?

A

Thin, protein tubes, which allow bacteria to stick to surfaces. They are not found in all bacteria.

207
Q

What are mesosomes?

A

Mesosomes are infolded in the plasma membrane of the bacterial cell wall. These are rich in enzymes that helps to perform functions like cellular respiration,DNA replication,secretion of glycocalyx and cell division(most imporatant function; it increases the surface area of the cell membrane).

208
Q

What are the size of ribosomes in prokaryote?

A

Ribosomes are the size 70S which are made up of a 30S and a 50S subunit. The values for the individual subunits don’t add up to the value for the whole ribosome, since the rate of sedimentation is related in a complex way to the mass and shape of the molecule.

209
Q

Which organelle has another organelle inside it?

A

The nucleus

210
Q

Why do cells become specialised?

A
  • only some genes are switched on
  • the switched on genes produce active mRNA which is translated into proteins within the cell
  • the protein produced determine the specific structural and functional features of that cell
211
Q

Give evidence to show that epigenetic changes can be inherited.

A
  • 2000 mothers and babies in rural Gambia were studied: mothers who were pregnant in the rainy season had better diets, and more methylation in six of their genes than those mothers pregnant in the dry season.
  • People in a Swedish village were studied: it was found that the health conditions the people developed were correlated with the diet of their parents and grandparents.
212
Q

What happens during G1?

A

the complete DNA instructions in the cell must be duplicated.

213
Q

What happens during the G2 phase?

A

The cell futher grows and protein synthesis occurs.

214
Q

When does cytokinesis occur in the cell cycle?

A

Between mitosis and interphase

215
Q

What is cytoknesis?

A

The cytoplasm divides to form 2 new cells.

216
Q

How do you calculate the miotic index?

A

Percentage of cells dividing / percentage number of cells

217
Q

What diseases are stem cells used to treat?

A
  • Parkinson’s disease
  • multiple sclerosis
  • type 1 diabetes
  • Burn
218
Q

What is the benefit of therapeutic cloning?

A

Therapeutic cloning grows an organ from a person’s own cells and this means the problem of the organ being rejected is avoided.

219
Q

Describe the process of therapeutic cloning.

A

A diploid cell is removed from a patient needing a transplant. The cell’s nucleus is fused with an ovum, from which the haploid nucleus has been removed, and a diploid cell results. This process is somatic cell nuclear transfer. The stem cells arising from this could then be encoraged to become whatever tissue was needed.

220
Q

What is the difference between diploid and haploid cells?

A

The main difference between haploid and diploid cells is the number of chromosome sets found in the nucleus. Therefore, cells with two sets are diploid, and those with one set are haploid.

221
Q

How is a gene switched on?

A
  • Acetylation of histone proteins, around whcih DNA is wrapped, switches genes on by loosening its wrapping with his tone.
  • DNA demethylation switches genes on by allowing RNA polymerase to bind
222
Q

What can be used to separate nature from nature in humans?

A

Twin studies

Biology AS Level (4 decks)

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