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SNAB A level Biology > Unit 3 > Flashcards

Unit 3 Flashcards

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1
Q

Similarities between prokaryotes and eukaryotes

A
  • have a cytoplasm
  • have ribosomes
  • have a cell membrane
  • can have cell walls
  • flagellum (only sperm in eukaryotes)
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2
Q

Features of a prokaryote

A
  • dna is in a plasmid
  • pili
  • binary fission (how prokaryotes divide and multiply)
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3
Q

Features of a eukaryote

A
  • dna in nucleus
  • mitochondria
  • meiosis and mitosis
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4
Q

Describe protein trafficking

A
  1. Transcription of DNA and mRNA- mRNA leaves the nucleus
  2. The protein is synthesised on a ribosome and enters the rough ER
  3. As the protein moves through the rough ER, it assumes its 3D shape
  4. The vesicle containing the protein is pinched off from the rough ER and fuses with the golgi apparatus
  5. The protein is modified and then the vesicle containing the protein is pinched off and fuses with the cell surface membrane, releasing the protein
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5
Q

If a cell is formed by mitosis, does it have the diploid number of haploid number ?

A

It has the full number of chromosomes so it is the diploid number

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6
Q

If a cell is formed by meiosis, does it have the diploid number of haploid number ?

A

It has half the number of chromosomes so it is the haploid number

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7
Q

Describe meiosis

A
  1. Chromosomes replicate before division. After division, each chromosome is made up of two strands of genetic material
  2. The homologous pairs line up at the equator
  3. The DNA separates into 2 cells
  4. The 2 chromatids from each of the chromosome are pulled apart to create 4 daughter cells
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8
Q

How does meiosis result in genetic variation?

A

The independent assortment in meiosis is a form of genetic variation as the homologous pairs line up randomly

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9
Q

What is crossing over and when does it happen?

A

During the first division, homologous pairs come together and all 4 chromatids come into contact. At these contact points, the chromatids break and rejoin, exchanging sections of DNA. The point where the chromatids overlap is the chiasma.

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10
Q

What is linkage ?

A

When any 2 genes are close together on the same chromosome. The further apart they are, the less likely they are to be linked

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11
Q

Name to diseases that are sex linked

A

Colour blindess and haemophilia

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12
Q

How much of the cell cycle does interphase take up?

A

90%

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13
Q

What happens in interphase?

A

New cell organelles are synthesised and dna replication occurs

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14
Q

What happens in prophase?

A

Chromosomes condense and the chromatids join at the centromere. Spindle fibres form and the nuclear envelopes break down, forming a vesicle in the cytoplasm

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15
Q

What happens in metaphase?

A

The chromosome centromeres attach to spindle fibres in the middle of the cell

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16
Q

What happens in anaphase?

A

The centromeres split and move to each side of the cell.

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17
Q

What happens in telophase?

A

The reverse of prophase; the chromosomes unravel and the nuclear envelope reforms, creating 2 separate nuclei

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18
Q

What happens in cytoplasmic division ?

A

A ring of protein filaments bond to the cell membrane until the cell divides

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19
Q

Describe egg fertilisation

A
  1. The sperm travels towards and reaches the ovum
  2. Chemicals are released from the cells surrounding the ovum and triggers the acrosome reaction
  3. The acrosome swells and fuses with the sperm
  4. Digestive enzymes are released that break down the follicle cells and zona pellucida- the nuclei of the ovum and sperm fuse
  5. The sperm nucleus enters the ovum
  6. The cortical reaction thickens the zona pellucida and stops any more sperm entering the ovum
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20
Q

Describe the layers of an ovum from outside inwards

A
  • follicle cells
  • zona pellucida
  • cell surface membrane
  • cytoplasm
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21
Q

What is a totipotent stem cell?

A

A cell that can specialise into any type of cell

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22
Q

What is a Pluripotent cell?

A

A cell that can specialise into most type of cells

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23
Q

What is a multipotent cell?

A

A cell that can specialise into some type of cells

24
Q

What is a blastocyst?

A

A hollow ball containing pluripotent cells; the outside cells go to form the placenta

25
Q

Describe therapeutic cloning

A

The patient will have one of their diploid cells removed, which Is then used fused with an ovum from which the haploid nucleus has been removed. The result would be a diploid cell rather than a zygote; this is called somatic cell transfer

26
Q

What are iPSC’s?

A

They are induced pluripotent stem cells. They’re more ethical than embryonic cells as no embryos are involved, meaning that none are discarded

27
Q

What is HFEA and what rules did they make in terms of therapeutic cloning

A

HEFA is the Human Fertilisation and embryology authority and in 2004 they decided that when therapeutic cloning is used, the cloned embryos must be discarded after 14 days

28
Q

Describe how Dolly the clone sheep was created

A
  1. A cell is taken from a sheep and an egg is taken from a female sheep
  2. The nucleus is removed from the egg cell and is fused with the body cell from the sheep
  3. The embryo is implanted in a surrogate mother
29
Q

The way in which a gene is active or in active is due to …

A

Methylation or acetylation

30
Q

Explain why a gene is not expressed

A

A gene would be expressed as methylation of DNA and histones causes nucleosides to pack tightly together. Transcription factors therefore cannot bind the DNA

31
Q

Explain why a gene is expressed

A

A gene would not be expressed as acetylation results in loose lacking of nucleosomes. Transcription factors therefore can bind the DNA.

32
Q

Who discovered that you could switch on an individual gene and what did they find out?

A

Jacob and Monod used E Coli in an experiment and found out that they only produce the enzyme B-galactosidase when lactose is present

33
Q

Describe how a gene is switched on when lactose is absent

A
  1. Repressive molecule binds to operator gene
  2. This blocks the RNA Polymerase from binding to the operator gene
  3. This inhibits the B-galactosidase
34
Q

Describe how a gene is switched off when lactose is present

A
  1. Lactose binds to the depressor molecule which inhibits the operator gene
  2. This allows through the RNA polymerase to bind to the operator gene
  3. This turns on the B-galctosidase gene and transcription is triggered
35
Q

What happens when gene expression goes wrong ?

A

Fibrodysplasia ossificans progressiva is a rare disease and is characterised by the growth of bones in odd places. It is caused by a gene mutation where one of the genes in the WBC is not switched off

36
Q

How are cells organised into tissues?

A

Adhesion molecules on the surface of the cell surface membrane help cells to recognise other cells like themselves and stick to them. Recognition proteins determine which cells work together in tissues and organs.

37
Q

Describe a cell

A

A multicellular organism specialised for a particular function

38
Q

Describe a tissue

A

A group of similar specialised cells that work together to carry out a function

39
Q

What is an organ?

A

A group of tissues working together to carry out one function

40
Q

What is an organ system?

A

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

41
Q

What are master genes?

A

They are genes that control development in each segment of the body

42
Q

How were master genes discovered?

A

Looking at mutations that cause the development of the wrong appendage for a certain segment.

43
Q

What do master genes produce?

A

mRNA that is translated into signal proteins. These proteins switch on genes responsible for producing proteins needed for specialisation in cells.

44
Q

What is melanin and where is it made?

A

Melanin is the dark pigment found in skin and hair and is made in melanocytes

45
Q

Making melanin with low UV exposure

A
  1. MSH is made and put into MSH receptors on the melanocyte
  2. Melanin is made and put into melanocytes
  3. Melanosomes are transferred to the skin cells
  4. Melanosomes collect around the nucleus, protecting it from UV damage
46
Q

Making melanin with high UV exposure

A
  1. More MSH is produced
  2. More MSH receptors form on the melanocyte
  3. More melanin is produced
  4. More melanin gathers around the nucleus protecting it from UV damage
47
Q

What enzyme do animals use to make melanin?

A

Tyrosinase

48
Q

What does tyrosinase do?

A

Tyrosinase catalyses the first step along a chemical pathway, changing the amino acid tyrosine into melanin.

49
Q

Describe what happens if an animal has a mutant allele for tyrosinase

A

The enzyme is made but it is unstable and inactivated at normal body temperature meaning the tips of their tail, paws and ears (the coldest parts of the body) are darker than the rest of their bodies

50
Q

How does cancer occur?

A

When cell multiplication is faster than cell death

51
Q

Often when cancer is inherited there is a mutation occurs before pregnancy. At what stage does the mutation occur

A

When gametes are made in meiosis

52
Q

Describe the role of oncogenes

A

They code for proteins that stimulate the transition from stage of the cell cycle to the next. DNA mutations in these genes mean that the cell cycle would be continuous

53
Q

Describe the role of tumour suppressor genes

A

They produce a suppressor that stops the cell cycle. A DNA mutation would mean that the cell cycle would have no breaks

54
Q

What would happen if there was a mutation in the oncogenes and tumour suppressor genes?

A

The cell cycle would have no breaks (continual) meaning that cells would be constantly made, causing a tumour

55
Q

Suggest how a stem cell can be differentiated

A
  1. Chemical stimulus detected by receptors
  2. Switches on/off gene
  3. mRNA is only made in active genes
  4. Protein is made
  5. This determines the structure so cell is permanently modified

SNAB A level Biology (8 decks)

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