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Bio AS paper 2 > Topic 3: Cell structure, mitosis and meiosis, epigenetics, stem cells > Flashcards

Topic 3: Cell structure, mitosis and meiosis, epigenetics, stem cells Flashcards

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Biology 101 flashcards
1
Q

Features of rough endoplasmic reticulum

A
  • A series of flattened sacs enclosed by a membrane with ribosomes
  • RER folds and processes proteins made on the ribosomes often located close to the nucleus
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2
Q

Features of smooth endoplasmic reticulum

A
  • Membrane bound sacs
  • SER produces and processes lipids
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3
Q

Features of Golgi apparatus

A

-Curved sacs with vesicles
-Modifies and packages proteins and lipids

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4
Q

Features of mitochondria

A

-Oval shaped, have a double membrane
-Inner membrane is folded to form cristae
-Fluid matrix on inside containing enzymes needed for cellular respiration

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5
Q

Features of centrioles

A

Hollow cylinders containing a ring of microtubules arranged at right angles to each other. Centrioles are involved in cell division

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6
Q

Explain the cell wall

A

Rigid outer covering made of peptidoglycanand cellulose which provides the cell with strength and support

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7
Q

Explain the slime capsule

A

-Protective slime layer
-Helps cell to retain moisture and adhere to surfaces

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8
Q

Explain 80s ribosomes

Explain 70s ribosomes

A

80s - Site of protein synthesis in eukaryotic cells
70s - Site of protein synthesis in prokaryotik cells

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9
Q

3 stages of interphase

A

G1 - Gap phase 1
S - Synthesis phase
G2 - Gap phase 2

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10
Q

What happens in G1 phase?

A

-Cell grows and DNA replicates.
-Cell makes RNA, enzymes and other proteins required for growth

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11
Q

What happens in S phase?

A

Chromosomes are replicated and begin to condense to form chromatin

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12
Q

What happens during G2 phase?

A

Cell continues to grow and the new DNA that has been synthesised is checked and any errors are usually repaired

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13
Q

Summary of interphase

A

G1 and G2 phases deal with protein synthesis, formation of organelles and membranes

S phase is when DNA synthesis takes place

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14
Q

What happens during Cytokinesis?

A

The whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells

In animal cells, cytokinesis involves constriction of the cytoplasm between the two nuclei and in plant cell a new cell is formed

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15
Q

Outline Prophase

A

-Chromosomes condense
-Nucleolus disappears and nuclear membrane begins to break down
-Centrioles move to opposite ends of cell and spindle fibres begin to form, attaching to centromere of each chromosome

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16
Q

Outline Metaphase

A

-Centrosomes reach opposite poles
-Chromosomes align in the centre of the cell

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17
Q

Outline Anaphase

A

-Chromosomes divide into two, spindle fibres shorten, pulling sister chromatids to opposite ends of the cell

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18
Q

Outline Telophase

A

-Nuclear membrane begins to form again
-Spindle fibres break down

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19
Q

Why is mitosis so important?

A

-Allows growth of multicellular organisms
-Replacement of cells and repair of tissues - cells can be repaired via mitosis. As cells are constantly dying they need to be replaced by genetically identical cells
-Asexual reporduction

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20
Q

Which structures does a plant cell contain that an animal cell doesn’t?

A

Cell wall
Plasmodesmata
Chloroplasts
Amyloplasts

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21
Q

Bacterial DNA is … (1)

A) circular and surrounded by a nuclear membrane
B) circular with no nuclear membrane
C) linear and surrounded by a nuclear membrane
D) linear with no nuclear membrane

A

B - Circular with no DNA

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22
Q

DNA synthesis in bacterial cell cultures has been investigated.
Describe how DNA is organised in a bacterial cell. (3)

A

-Large circular DNA
-Several small plasmids
-DNA isn’t located in the nucleus but in the cytoplasm

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23
Q

Describe what happens to lysosomes once their contents have been digested. (2)

A

-Lysosomes fuse with cell surface membrane
-Contents of the lysosome are released from the cell via exocytosis

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24
Q

Which of the following structures is found in animal cells? (1)
A) amyloplast
B) chloroplast
C) mesosome
D) ribosome

A

D - Ribosome

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25
Q

Which of the following structures is found only in plant cells? (1)
A) amyloplast
B) Golgi apparatus
C) mesosome
D) vacuole

A

A - Amyloplast

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26
Q

Which of the following structures is found in both animal and plant cells? (1)
A) amyloplast
B) cell wall
C) pili
D) smooth endoplasmic reticulum

A

D - Smooth endoplasmic reticulum

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27
Q

The red squirrel population on Brownsea Island has been affected by a disease
caused by a prokaryotic organism.

Scientists took blood samples from infected red squirrels and analysed them using an electron microscope.

Describe the features that could be used to identify the prokaryotic cells in the blood sample (4)

A

Presence of a cell wall
Plasmid DNA
Pili/flagellum
70s ribosomes
Capsule

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28
Q

Explain why the nucleus cannot be observed at the end of prophase in a eukaryotic cell (2)

A

-Because nuclear membrane is broken down
-Because DNA is coiled up/condensed into individual chromosomes

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29
Q

Some diseases are linked to a failure in the endoplasmic reticulum (ER).
Cells of people with these diseases contain proteins that are folded incorrectly.
Some of these proteins are enzymes.
Protein synthesis in eukaryotic cells occurs in (1)

A) 70S ribosomes in the nucleus
B) 70S ribosomes on the endoplasmic reticulum
C) 80S ribosomes in the nucleus
D) 80S ribosomes on the endoplasmic reticulum

A

D

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30
Q

Many of the proteins synthesised become extracellular enzymes.
Describe what happens to these proteins following the process of translation until they are released from the cell.
(3)

A

-The proteins are folded in the RER
-Proteins are packaged into vesicles
-Protein is modified in the Golgi apparatus
-Exocytosis

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31
Q

Cells in people with these diseases produce incorrectly folded enzyme molecules.
Explain why enzymes that are incorrectly folded cannot carry out their function (3)

A

-If the protein isn’t folded correctly the tertiary structure would be different
-The active site of the enzyme would not fit with the substrate, cant form an enzyme-substrate complex
-So it cant catalyse the reaction

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32
Q

In prokaryotic cells, ribosomes are (1)
A) absent
B) larger than ribosomes in eukaryotic cells
C) smaller than ribosomes in eukaryotic cells
D) the same size as ribosomes in eukaryotic cells

A

C

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33
Q

Some bacteria have a capsule that is located … (1)

A) between the cell wall and the cell membrane
B) in the cytoplasm
C) inside the cell wall
D) outside the cell wall

A

D

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34
Q

How do stem cells differentiate?

A

-Differential gene expression

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35
Q

Outline the process of differentiation

A

-Under certain conditions, some genes in the stem cells will be activated, whilst others are inactivated

-mRNA is transcribed from active stem cells

-This mRNA is then translated to form proteins

-These proteins are responsible for modifying the cell

-As these proteins continue to modify, the cell become increasingly specialized

-The process of specialization is irreversible

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36
Q

Explain the process of gene switching

A

RNA polymerase binds to the promoter region. Transcription will only occur when the enzyme is attached.
Before then, the gene is ‘switched off’.
A regulator protein is also regulated to begin transcription

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37
Q

What is a stem cell?

A

An undifferentiated cell which can become any type of cell. They can divide by mitosis an unlimited number of times

38
Q

What are the 3 types of stem cells?

A
  • Multipotent cells, which can give rise to many different types of cells.
  • Pluripotent cells which are able to give rise to many types of specialised cells, but not placental cells.
  • Totipotent cells which can give rise to all / any types of specialised cells, including
    placental cells.
39
Q

Uses of stem cells and where are they gathered from?

A

Embryonic stem cells = Come from the embryo
Adult stem cells = Bone marrow

Uses:
Clinical drug testing
Bone marrow transplants
Replace damaged tissues
Treat Parkinson’s, diabetes and multiple sclerosis

40
Q

Pros of using stem cells

A

-Treat Parkinson’s disease - Stem cell transplants may allow replacement of damaged brain cells
-Diabetes - stem cell therapy could give patients working pancreas cells and restore insulin production
-Nerve damage - Brain and spinal cord don’t regrow so stem cell therapy could help save patients with nerve damage

41
Q

Cons of using stem cells

A

-Many people believe use of stem cells is unethical as embryos are killed in the process of embryonic stem cell extraction.
-There’s a risk of infection when cells are transplanted, and they could become cancerous

42
Q

What is a transcription factor?

A

-A protein that controls transcription of genes by binding to a specific region of DNA
-They ensure that genes are being expressed correctly
-They allow organisms to respond to their environments
-Either assist or inhibit RNA polymerase binding or not binding to the gene

43
Q

What is an activator?

A

A transcription factor which helps RNA polymerase bind to the DNA at the start of a gene and begins transcription of that gene

44
Q

What is a repressor?

A

A transcription factor which stops RNA polymerase from binding to the DNA at the start of a gene inhibiting transcription of that gene

45
Q

Transcription factors that decrease the rate of transcription are known as…

A

REPRESSORS

46
Q

Transcription factors that increase the rate of transcription are known as…

A

ACTIVATORS

47
Q

What is an operon?

A

A section of DNA that has:
-A cluster of structural genes that are transcribed together
-Control elements like promoter and operator regions
-Some operons may include regulatory genes that code for activators or repressors

48
Q

What is a lac operon?

A

-Found in some bacteria cells
-Lac operon controls the production of the enzyme lactase
-Lactase breaks down the substrate lactose so it can be used as energy in the cell

49
Q

Explain the structure of the lac operon

A

Components in the lac operon in the following order:
-Promoter for structural genes
-Operator
-LacZ
-LacY
-LacA

Located to the left (upstream) of the lac operon on the bacterium’s DNA there is also the:
-Promoter for regulatory gene
-Regulatory gene lacI that codes for the lac repressor protein

50
Q

Explain the process when lactose is absent in the medium bacteria growing in

A

-The regulatory gene is transcribed and translated to produce lac repressor protein

  • The lac repressor protein binds to the operator region upstream of lacZ

-Due to the presence of the repressor protein RNA polymerase is unable to bind to the promoter region

-Transcription of the structural genes does not take place and as a result, no lactase enzyme is synthesised

51
Q

Explain the process when lactose is present in the medium bacteria is growing in

A

-There is an uptake of lactose by the bacterium

-The lactose binds to the second binding site on the repressor protein, distorting its shape so that the repressor protein cannot bind to the operator region

-RNA polymerase is then able to bind to the promoter region and transcription takes place

-The mRNA from all three structural genes is translated

-The enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium

52
Q

What is meant by epigenetics?

A

A heritable change in gene function without a change in DNA base sequence

53
Q

How are epigenetic changes passed on?

A

The changes affect cell division, all cells that arise from the altered cells will possess the modifications. This includes gametes meaning the changes are heritable

54
Q

What are the two types of epigenetic changes?

A

Methylation - DNA
Acetylation - Histones modification - changes to amino acids

55
Q

Explain Methylation

A

-Involves the addition of a methyl group (CH3) directly onto the DNA
- Added to the cystine base next to guanine, it only happens if guanine is next to cytosine
-Methylation of DNA suppresses the transcription of the gene
-Prevents transcription factor from binding to promoter or any other enzyme needed for transcription
-Methylation is affected by; smoking, diet, stress, exercise, age

56
Q

Explain acetylation

A

-An acetyl group (COCH3) gets added onto the amino acid lysine
-Lysine has an overall positive charge and it allows DNA to be held tight
-If an acetyl group is added to the lysine amino acid, it will remove the positive charge of the lysine and therefore remove the strong bond between the DNA and the histone
-DNA is able to unravel allowing RNA polymerase to sit on the promoter region of the gene and is expressed

57
Q

Explain how epigenetic changes can cause differences in a characteristic (3)

A

-Histone modification/DNA methylation
-Affects activation/deactivation of genes
-This affects enzyme production

58
Q

Explain how epigenetic changes affect the activation of genes in daughter cells (3)

A

-Genes are activated/deactivated in stem cells
-Due to DNA methylation and histone modification
-Therefore same genes will be activated in the daughter cells

59
Q

In eukaryotic cells, two organelles with a double membrane are …(1)
A) The nucleus and smooth endoplasmic reticulum
B) a nucleus and a mitochondrion
C) a mitochondrion and a ribosome
D) a mitochondrion and smooth endoplasmic reticulum

A

B

60
Q

White blood cells, plant cells and prokaryotic cells all contain… (1)
A) a nucleus
B) Golgi apparatus
C) ribosomes
D) smooth endoplasmic reticulum

A

C

61
Q

A structure present in prokaryotic cells but not present in a white blood cell is… (1)
A) a cell wall
B) a centriole
C) a ribosome
D) rough endoplasmic reticulum

A

A

62
Q

The primary structure of this protein is then converted into a tertiary structure and modified by organelles in the cell

Describe the role of the organelles involved in these processes (5)

A

-Folding of protein inside the rER
-Bonds formed between R groups
-rER packages proteins in vesicles
-Vesicles transport the protein to Golgi apparatus
-Protein modified in Golgi apparatus

63
Q

Many of the proteins synthesised become extracellular enzymes

Describe what happens to these proteins following the process of translation until they are released from the cell (3)

A

-The proteins are folded in the rER
-The proteins are packaged and transported in vesicles
-Proteins is modified in Golgi apparatus
-The proteins are then exocytosed

64
Q

Explain why DNA is being replicated before mitosis begins (2)

A

-To ensure there is a diploid number of chromosomes in each daughter cell
-To ensure daughter cells are genetically identical

65
Q

Explain how a large number of cells with the same phenotype can be produced in a tissue (2)

A

-Phenotype is determined by the genotype and the effect of the environment
-Mitosis produces cells with the same genotype

66
Q

Describe what happens inside a cell during prophase of mitosis (4)

A

-The chromosomes condense
-Centrioles move to opposite pole of the cell
-Spindle fibres form
-Nucleolus breaks down
-The nuclear envelope breaks down

67
Q

Describe what happens in the cell during the telophase stage of mitosis (4)

A

-Spindle fibres break down
-Chromosomes decondense
-Nucleolus reforms
-Nuclear membrane forms

68
Q

Describe what is meant by the term tissue (2)

A

A group of similar cells which work together for a common function

69
Q

State one difference between a tissue and an organ (1)

A

A tissue is made up of one type of cell but an organ is made of different tissues

70
Q

Describe how meiosis leads to genetic variation in the gametes produced (2)

A

-Produces non-identical gametes due to independent assortment of chromosomes
-Crossing over between chromatids of chromosomes

71
Q

Explain how crossing over may differ in sex chromosomes (2)

A

-Crossovers cannot form between some sections of the X and Y chromosome
-Because there is a difference in size of X and Y chromosomes

72
Q

Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells (4)

A

Similarity:
-Both increase the number of cells

Differences:
-Mitosis produces diploid cells and meiosis produces haploid cells

-Meiosis produces cells that are genetically different to each other whereas mitosis produces genetically identical cells

-Mitosis results in 2 daughter cells whereas meiosis results in 4 daughter cells

73
Q

Even though both offspring are from the same father and the same mother they may be genetically different

Explain thy the offspring may be genetically different (2)

A

Each gamete contains different combinations of alleles due to crossing over during meiosis

74
Q

Explain how crossing over can lead to genetic variation (3)

A

-Swapping of genetic material
-Between non-sister chromatids
-Resulting in different combinations of alleles

75
Q

Variation between children and their parents is affected by linkage of genes

Explain why some genes show linkage and other show sex linkage (3)

A

-There are more genes than there are chromosomes

-Linkage relates to genes for different characteristics located on the same chromosome

-Sex linkage relates to genes on the sex chromosome

76
Q

Factors such as the diet of the mother during pregnancy can cause epigenetic changes in the embryo

Explain how epigenetic changes affect the development of tissues in the embryo (3)

A

-DNA is wrapped around histones
-Acetylation of the histone affects chromosome unwinding
-Methylation of DNA affects transcription of genes
-Therefore gene expression is altered

77
Q

Explain how epigenetic changes can cause differences in a characteristics (3)

A

Histone modification/DNA methylation affects activation of genes which affects enzyme production

78
Q

As pluripotent stem cells divide, epigenetic changes are passed on

Explain how epigenetic changes affect the activation of genes in daughter cells (3)

A

-Genes are activated in the stem cells
-Due to either DNA methylation or histone modification
-So the same genes will be activated in the daughter cells

79
Q

Explain how DNA methylation can modify the activation of a gene (3)

A

-Methyl group attached to DNA
-Which prevents transcription
-Transcription factors cannot bind to promoter region
-Deactivating the gene

80
Q

State what is meant by the term pluripotent (2)

A

-Pluripotent stem cells can differentiate and give rise to many cell types
-Some genes in pluripotent stem cells are inactivated and therefore they cannot differentiate into all cell types

81
Q

Describe how society controls the use of embryonic stem cells in medical research (4)

A

-Regulatory bodies/laws/high court
-Society determines moral aspects
-Checking source of stem cells is acceptable
-Decide on maximum age of embryo allowed for research

82
Q

Explain why stem cells from the heart cannot be used to grow cells to repair the cornea (3)

A

-Cells are not totipotent
-Some genes have already been activated and deactivated
-Therefore, will not be able to specialise into cornea

83
Q

Give the meaning of the term totipotent (2)

A

A cell that has the ability to differentiate into all cell types

84
Q

Explain how a bone marrow stem cell can give rise to red blood cells (4)

A

-By differentiation
-Due to a certain stimuli
-Certain genes are activated or deactivated
-mRNA is transcribed from these active genes only to produce haemoglobin

85
Q

Explain why chemicals from the eye are needed to produce corneal cells from a suitable stem cell (4)

A

-Chemicals cause some genes, relating to the cornea, to be activated or deactivated
-mRNA is transcribed from these active genes only
-This mRNA is then translated to form proteins
-Which are responsible for modifying the cell into a corneal cell

86
Q

Describe how cells become specialised (3)

A

-Due to a certain (chemical) stimulus, certain genes are switched on or off
-mRNA is transcribed from these active genes only
-This mRNA is then translated to form proteins responsible for modifying the cell

87
Q

Beta cells in the pancreas produce insulin when there is an increase in glucose levels in the blood

Transcription factors are involved in the activation of the insulin gene

Explain how transcription factors could activate insulin gene expression in beta cells (3)

A

-Interaction between transcription factors and promoter region

-RNA polymerase binds to promoter region

-Transcription for insulin gene

88
Q

Extracellular enzymes are produced by specialised cells.

Explain how groups of cells can produce the same enzyme (3)

A

-Genes can be activated or deactivated
-These cells receive the same stimulus
-These cells have the gene for the enzyme activated
-Resulting in production of mRNA for the enzyme

89
Q

Describe how mesenchymal stem cells can give rise to different types of cell (4)

A

-Different stimulus activates different genes
-mRNA is transcribed from these active genes only
-mRNA is then translated to form proteins
-These proteins determine structure/function of cells
-Different genes activated result in different types of cells being produced

90
Q

Explain why an individual may have a greater adult height than their biological parents (3)

A

-Height is affected by the environment as well as genotype
-Height is an example pf polygenic inheritance
-Therefore offspring can inherit a mixture of alleles from both parents that increase height
-E.g. high protein diet, more calcium

91
Q

State what is meant by the term operon (2)

A

A section of DNA, controlled by a single operator/promoter

92
Q

Describe the effect of lactose on the lac operon (3)

A

-Lactose allows the lac operon to function
-RNA polymerase can now bind to promoter region and repressor no longer binds to operator
-Allowing transcription to happen

Bio AS paper 2 (6 decks)

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