Topic 3: Cell structure, mitosis and meiosis, epigenetics, stem cells Flashcards
(126 cards)
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
2
Q
Features of smooth endoplasmic reticulum
A
- Membrane bound sacs
- SER produces and processes lipids
3
Q
Features of Golgi apparatus
A
-Curved sacs with vesicles
-Modifies and packages proteins and lipids
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
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
6
Q
Explain the cell wall
A
Rigid outer covering made of peptidoglycan and cellulose which provides the cell with strength and support
7
Q
Explain the slime capsule
A
-Protective slime layer
-Helps cell to retain moisture and adhere to surfaces
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
9
Q
What happens in G1 phase?
A
-Cell grows and DNA replicates.
-Cell makes RNA, enzymes and other proteins required for growth
10
Q
What happens in S phase?
A
Chromosomes are replicated and begin to condense to form chromatin
11
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
12
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
13
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
14
Q
Outline Metaphase
A
-Centrosomes reach opposite poles
-Chromosomes align in the centre of the cell
15
Q
Outline Anaphase
A
-Chromosomes divide into two, spindle fibres contract and shorten, pulling sister chromatids to opposite ends of the cell
16
Q
Outline Telophase
A
-Nuclear membrane begins to form again
-Spindle fibres break down
-Chromosomes decondense
-Nucleolus reappears
17
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 reproduction
18
Q
Which structures does a plant cell contain that an animal cell doesn’t?
A
Cell wall
Plasmodesmata
Chloroplasts
Amyloplasts
19
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
20
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
21
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
22
Q
Which of the following structures is found in animal cells? (1)
A) amyloplast
B) chloroplast
C) mesosome
D) ribosome
A
D - Ribosome
23
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
24
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
25
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)
Presence of a cell wall
Plasmid DNA
Pili/flagellum
70s ribosomes
Capsule
26
Explain why the nucleus cannot be observed at the end of prophase in a eukaryotic cell (2)
-Because nuclear membrane is broken down
-Because DNA is coiled up/condensed into individual chromosomes
27
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
D
28
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)
-The proteins are folded in the RER
-Proteins are packaged into vesicles
-Protein is modified in the Golgi apparatus
-Exocytosis
29
Cells in people with these diseases produce incorrectly folded enzyme molecules.
Explain why enzymes that are incorrectly folded cannot carry out their function (3)
-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
30
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
C
31
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
D
32
How do stem cells differentiate?
-Differential gene expression
33
Outline the process of differentiation
-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
34
What is a stem cell?
An undifferentiated cell which can become any type of cell. They can divide by mitosis an unlimited number of times
35
What are the 3 types of stem cells?
-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.
36
Uses of stem cells and where are they gathered from?
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
37
Pros of using stem cells
-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
38
Cons of using stem cells
-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
39
What is a transcription factor?
-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
40
What is an activator?
A transcription factor which helps RNA polymerase bind to the DNA at the start of a gene and begins transcription of that gene
41
What is a repressor?
A transcription factor which stops RNA polymerase from binding to the DNA at the start of a gene inhibiting transcription of that gene
42
Transcription factors that decrease the rate of transcription are known as...
REPRESSORS
43
Transcription factors that increase the rate of transcription are known as...
ACTIVATORS
44
What is an operon?
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
45
What is a lac operon?
-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
46
Explain the structure of the lac operon
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
47
Explain the process when lactose is absent in the medium bacteria growing in
-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
48
Explain the process when lactose is present in the medium bacteria is growing in
-There is an uptake of lactose by the repressor
-The lactose binds to the 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
49
What is meant by epigenetics?
A heritable change in gene function without a change in DNA base sequence
50
How are epigenetic changes passed on?
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
51
What are the two types of epigenetic changes?
Methylation - DNA
Acetylation - Histones modification - changes to amino acids
52
Explain Methylation
-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
53
Explain acetylation
-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 bind to the promoter region of the gene and is expressed
54
Explain how epigenetic changes can cause differences in a characteristic (3)
-Histone modification/DNA methylation
-Affects activation/deactivation of genes
-This affects enzyme production
55
Explain how epigenetic changes affect the activation of genes in daughter cells (3)
-Genes are activated/deactivated in stem cells
-Due to DNA methylation and histone modification
-Therefore same genes will be activated in the daughter cells
56
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
B
57
White blood cells, plant cells and prokaryotic cells all contain... (1)
A) a nucleus
B) Golgi apparatus
C) ribosomes
D) smooth endoplasmic reticulum
C
58
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
59
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)
-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
60
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)
-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
61
Explain why DNA is being replicated before mitosis begins (2)
-To ensure there is a diploid number of chromosomes in each daughter cell
-To ensure daughter cells are genetically identical
62
Explain how a large number of cells with the same phenotype can be produced in a tissue (2)
-Phenotype is determined by the genotype and the effect of the environment
-Mitosis produces cells with the same genotype
63
Describe what happens inside a cell during prophase of mitosis (4)
-The chromosomes condense
-Centrioles move to opposite pole of the cell
-Spindle fibres form
-Nucleolus breaks down
-The nuclear envelope breaks down
64
Describe what happens in the cell during the telophase stage of mitosis (4)
-Spindle fibres break down
-Chromosomes decondense
-Nucleolus reforms
-Nuclear membrane forms
65
Describe what is meant by the term tissue (2)
A group of similar cells which work together for a common function
66
State one difference between a tissue and an organ (1)
A tissue is made up of one type of cell but an organ is made of different tissues
67
Describe how meiosis leads to genetic variation in the gametes produced (2)
-Produces non-identical gametes due to independent assortment of chromosomes
-Crossing over between chromatids of chromosomes
68
Explain how crossing over may differ in sex chromosomes (2)
-Crossovers cannot form between some sections of the X and Y chromosome
-Because there is a difference in size of X and Y chromosomes
69
Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells (4)
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
70
Even though both offspring are from the same father and the same mother they may be genetically different
Explain why the offspring may be genetically different (2)
Each gamete contains different combinations of alleles due to crossing over during meiosis
71
Explain how crossing over can lead to genetic variation (3)
-Swapping of genetic material
-Between non-sister chromatids
-Resulting in different combinations of alleles
72
Variation between children and their parents is affected by linkage of genes
Explain why some genes show linkage and other show sex linkage (3)
-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
73
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)
-DNA is wrapped around histones
-Acetylation of the histone affects chromosome unwinding
-Methylation of DNA affects transcription of genes
-Therefore gene expression is altered
74
Explain how epigenetic changes can cause differences in a characteristics (3)
-Histone modification/DNA methylation
-Affects activation of genes
-Which affects enzyme production
75
As pluripotent stem cells divide, epigenetic changes are passed on
Explain how epigenetic changes affect the activation of genes in daughter cells (3)
-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
76
Explain how DNA methylation can modify the activation of a gene (3)
-Methyl group attached to DNA
-Which prevents transcription
-Transcription factors cannot bind to promoter region
-Deactivating the gene
77
State what is meant by the term pluripotent (2)
-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
78
Describe how society controls the use of embryonic stem cells in medical research (4)
-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
79
Explain why stem cells from the heart cannot be used to grow cells to repair the cornea (3)
-Cells are not totipotent
-Some genes have already been activated and deactivated
-Therefore, will not be able to specialise into cornea
80
Give the meaning of the term totipotent (2)
A cell that has the ability to differentiate into all cell types
81
Explain how a bone marrow stem cell can give rise to red blood cells (4)
-By differentiation
-Due to a certain stimuli
-Certain genes are activated or deactivated
-mRNA is transcribed from these active genes only to produce haemoglobin
82
Explain why chemicals from the eye are needed to produce corneal cells from a suitable stem cell (4)
-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
83
Describe how cells become specialised (3)
-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
84
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)
-Interaction between transcription factors and promoter region
-RNA polymerase binds to promoter region
-Transcription for insulin gene
85
Extracellular enzymes are produced by specialised cells.
Explain how groups of cells can produce the same enzyme (3)
-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
86
Describe how mesenchymal stem cells can give rise to different types of cell (4)
-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
87
Explain why an individual may have a greater adult height than their biological parents (3)
-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
88
State what is meant by the term operon (2)
A section of DNA, controlled by a single operator/promoter
89
Describe the effect of lactose on the lac operon (3)
-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
90
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)
-Interaction between transcription factors and promoter (region on gene) (1)
-RNA polymerase binds (to promoter region) (1)
-{Transcription /mRNA produced } (for insulin gene) (1)
91
Describe the events that occur during prophase in an animal cell (3)
-Spindle fibres form
-Nuclear envelope breaks down
-Chromosomes condense
-Centrioles move to opposite ends of the cell
92
In which stage of cell division do spindle fibres attach to the centromeres?
A) anaphase
B) interphase
C) metaphase
D) telophase
C
93
In which stage of the cell division does the nuclear membrane start to
break down?
A) interphase
B) metaphase
C) prophase
D) telophase
C
94
In which stage of cell division are chromatids first visible when using a light microscope?
A) interphase
B) metaphase
C) prophase
D) telophase
C
95
The lac operon is found in some prokaryotes
Describe what is meant by the term operon (2)
-A group of genes / a section of DNA
-Controlled by a single operator/ promotor / that are transcribed together
96
Describe the effect of lactose on the lac operon (3)
-Lactose allows the lac operon to function
-RNA polymerase can now bind to promoter region / repressor molecule no longer binds to operator
-Allowing transcription / mRNA to be synthesised
-So enzymes involved in metabolising / breaking down lactose are made
97
Describe two different social issues related to the use of PGD (2)
-Selecting one embryo over another / loss of a potential life
-Risk of identifying other conditions / selecting for other characteristics
-Costly / emotional strain as not always accurate
98
Describe the appearance of the chromosomes in the cells undergoing the metaphase stage of mitosis (3)
-Condensed / visible
-Seen as pairs of chromatids held together by a centromere
-Joined to the spindle fibres
-Aligned on the equator of the cell
99
It is claimed that the percentage of cells in a root tip undergoing mitosis during the day is different from the percentage during the night
Devise an investigation to test this hypothesis (5)
-Use same source of root tips
-Control temperature by growing the plants in the same conditions
-Use orcein to stain the cells
-Squash under a coverslip / on a microscope slide
-Calculate mitotic index for both conditions
100
State two properties of an organ (2)
-Made up of many different types of cell / more than one type of tissue
-Tissues working together for various functions / to carry out an overall function
101
Explain how vesicles are involved in the successful fertilisation of an egg cell by only one sperm (2)
-Cortical granules fuse with the egg cell surface membrane
-Releasing contents / enzyme that harden / thicken zona pellucida
102
Paclitaxel is a drug used in the treatment of cancer
Cancer involves cells dividing repeatedly in an uncontrolled manner
Paclitaxel prevents spindle fibres from changing length
Deduce why Paclitaxel prevents cell division (3)
-Shortening of spindle fibres separates the chromatids
-If spindle fibres cannot shorten, the chromatids / chromosomes cannot be pulled to opposite poles of the cell
-If the spindle fibres cannot shorten the cell cannot enter anaphase / mitosis cannot be completed
103
Give two reasons why sieve tube element cells do not require rough endoplasmic reticulum and ribosomes (2)
-There will be no transcription / mRNA therefore ribosomes not required for translation
-No proteins will be synthesised to be produced in endoplasmic reticulum
104
Role of centrioles (1)
Spindle organisation
105
Describe how the cells process this polypeptide and secrete it as an enzyme (4)
-Polypeptide is folded within the rough endoplasmic reticulum
-Packaged into vesicles
-Transport vesicles fuse with Golgi apparatus
-Polypeptide is modified within the Golgi apparatus
-Exocytosis / vesicle fuses with cell surface membrane
106
Definition of a gene
A length of DNA that codes for a single polypeptide or protein
107
Males only have 1 X chromosome …
-Means they are much more likely to show sex-linked recessive conditions (such as red-green colour blindness)
-Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele
108
Monogenic meaning
Some characteristics (i.e. the phenotype) are controlled by a single gene - these characteristics are known as monogenic
These characteristics usually show discontinuous variation (e.g. blood group)
109
Polygenic meaning
Characteristics are controlled by several genes - these characteristics are known as polygenic
These characteristics usually show continuous variation (e.g. height, mass, skin colour)
110
Explain what is meant by an inherited recessive disorder (2)
-A recessive disorder is one caused by a faulty allele
-That is only expressed in the homozygous condition / absence of a normal allele
111
Role of ribosomes in protein synthesis
-Ribosome holds mRNA
-Ribosome holds two tRNA
-So that peptide bonds can form between (adjacent) amino acids
-Site of protein synthesis
112
Role of Golgi apparatus in protein synthesis
-Golgi modifies the protein
-e.g. addition of carbohydrate group
-Protein moved into vesicles
-Exocytosis
113
Suggest how the addition of a chemical causes the human gene to be switched on (3)
-The chemical could be a transcription factor / hormone
-Transcription factor being activated (e.g. binds to transcription factor) or counters inhibitor
-ref to promoter region
-Transcription occurs e.g. RNA polymerase binds, mRNA produced
114
Suggest how a tumour suppressor gene could stop a potential tumour cell forming (2)
-Acts as an inhibitor of transcription / protein synthesis
-Meaning the gene isnt activated and no protein is produced
115
Cancer can be due to body cells continuing to undergo mitosis and cell division.
Prophase is one stage of mitosis.
Describe the events that occur during prophase in an animal cell. (3)
-Nucleus / nuclear envelope / nucleolus breaks down
-Spindle (fibres) formed
-Chromosomes / chromatids condense
-Centrioles migrate to (opposite) poles of the cell
116
Describe the appearance of the chromosomes in the cells undergoing the metaphase stage of mitosis (3)
-Condensed / visible
-Seen as pairs of chromatids (held together by a centromere)
-Joined to the spindle (fibres)
-Aligned on the equator of the cell
117
The hormone ghrelin may cause epigenetic changes to the FTO gene leading to weight gain
Describe how ghrelin could cause epigenetic changes (2)
-Methylation of DNA
-Modification of histones
-(therefore) affecting regulation
118
State two properties of an organ (2)
-Made up of many different types of cell / more than one type of tissue
-(tissues) working together for various functions / to carry out an overall function
119
Explain how the acetylcholinesterase gene can be expressed in some tissues but not others (3)
-Hormones / chemical signals bind to receptors found only in some cells
-Regulating a transcription factor
-Transcription factor binds to the promotor region of the gene
-Therefore switching on transcription of the gene
120
Melanophores produce a black pigment called melanin.
Explain how a specialised cell such as a melanophore is produced from a stem cell (3)
-Due to chemical stimulus / transcription factors
-Activating specific genes
-Resulting in synthesis of proteins / enzymes
-Involved in the synthesis of melanin
121
What is meant by epigenetics (2)
-Switching on and switching off of genes
-Without a change in DNA sequence
122
Explain why a change in the DNA sequence can change the phenotype of an organism (3)
-Change in the DNA causes a change to the amino acid sequence
-Protein has a different shape / tertiary structure
-So the function is altered
-Change in protein can alter structure or function of a cell
123
Describe the role of centromeres in mitosis (3)
-During metaphase, centromeres bind to spindle fibres and keep pairs of chromatids together
-Point at which the (sister) chromatids separate during anaphase
124
Describe the differences between pluripotent stem cells and totipotent stem cells (3)
-Totipotent stem cells have the potential to give rise to all cell types
-Pluripotent stem cells can give rise to { most / some } cell types
-Totipotent stem cells can give rise to a whole organism (pluripotent cannot)
-In totipotent stem cells no genes are inactivated / pluripotent stem cells have some genes inactivated
125
The zygote then divides by
A) meiosis to produce diploid cells
B) meiosis to produce haploid cells
C) mitosis to produce diploid cells
D) mitosis to produce haploid cells
C
126
Give two functions of the Golgi apparatus (2)
-Modifies proteins
-Packages proteins into vesicles
-Removes water from the protein / concentrates the { protein / glycoprotein } (1)
