Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biology A level > Topic 3- Notes > Flashcards

Topic 3- Notes Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What are prokaryotic cells?

A
  • Bacteria and cyanobacteria (photosynthetic bacteria) make up the prokanyotic kingdom
    _ No nucleus/membrane-bound cell organelles
  • extremely small - 0.5-5um
  • DNA lies free in the cytoplasm
  • Always has a cell wall
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a eukaryotic cell?

A
  • have discrete membrane bound organelles, -nuclei, mitochondria and chloroplasts (plants only)
  • 20 um+
  • don’t all have cell wall
  • organisms with eukaryotic cells are called eukaryotes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Plasma membrane
structure
function

A

Plasma membrane

A phospholipid bilayer with intrinsic and extrinsic protein molecules

A partially permeable barrier which controls the passage of substances into and out of the cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Golgi

A

Golgi
Stack of membrane bounded, flattened sacs in the cytoplasm lookin like a pile of pitta bread.

Receives proteins synthesised on the ER and prepares them for secretion from the cell. this often involves adding carbohydrate to the proteins to make them into glycoproteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Mitochondria

A

Has an outer membrane and an inner one which is folded to from cristae. Inside their inner membrane is the matrix containing enzymes , a circular DNA molecule and ribosomes.
The site of aerobic respiration and responsible for producing most of the ATP in the cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Cell wall

A

Cell wall
Consists of cellulose microfibrils and other polysaccharides
Provides mechanical support and protection. Prevents the cell from bursting.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Rough endoplasmic reticulum (RER)

A

A complex network of flattened, membrane-bounded sacs called cisternae. Has ribosomes attached to the cytoplasmic side.
Forms a system f channels for tranporting materials through the cytoplasm. Has ribosomes on its surface and is the site off protein synthesis.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Nucleus

A

Large organelle enclosed by a double membrane (an enveloppe) perforated by pores. Contains chromosomes and one or more nucleoli.
Chromosomes contain DNA which controls the synthesis of proteins. Ribosomes are formed in the nucleolus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Chloroplasts

A

Surrounded by two membranes. Contains a matrix called stroma which has a system of membranes running through it. These are stacked in places to form grana containing chlorophyll. Stroma contains circular DNA, ribosomes and starch grains.
The organells in which photosynthesis takes place. Pigmentss capture the energy of sunlight and transfer it to chemical bonds.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Ribosome

A

Very small organelle not bounded by a membrane. Consists of a large and a small sub unit. Made of protein and RNA.
Uses the information in nucleic acid to synthesise proteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

lysomome

A

A vesicle containing digestive enzymes

Responsible for destroying worn-out oganelles and for digesting the contents of vacuoles formed by phagocytosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Smooth ER

A

A complex network of flattened, membrane bound sacs called cistermae.
Forms a system of channels for transporting materials through the cytoplasm. Synthesises steroids and other lipids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Vacuole

A

A sac bounded by a single membrane. contains cell sap which is a solution of mineral salts, pigments, organic acids and other substances.
Stores waste products and other substances. Changes in volume affect the turgidity of the cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Cilia

A

Hair like extension sticking out from the surface of the cell. Each consists of a cylinder containing 9 microtubules arranged in a circle. There are also 2 microtubules in a central bundle.
Microtubules use energy from ATP to move resulting in a sweeping or rotating movement. (So the structures either waft to move substances across the cell, or spin to propel the cell itself).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Centroles

A

A pair of short cylinders. Each cylinder is made up of nine fibres.
From a spindle-shaped structure of protein fibres on which the chromosomes move during nuclear division.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are 2 important roles of meiosis?

A

1) to form 4 (sex/identical/gamete) cells with 1/2 the normal chromosome no. (reduction division) as the parent (diploid) cell. Meiosis comprises of 2 successive nuclear divisions, after DNA replication.
2) To introduce genetic variation through recombination of chromosomes. Variation is produced by random assortment of chromosomes and crossing over of non-sister chromatids. Fusion of gametes from different parents introduces further genetic variation through new combinations of alleles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Complete
A pair of homologous chromosomes is called a A. The combination of the four chromosomes is also called a B. The pairing process is called C.

A

A) Bivalent
B Tetra
c) synapsis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is genetic linkage?

A
  • The tendency of alleles that are nearer together on a chromosome to be inherited together.
  • During the first division of meiosis, the chromosomes come together in their pairs, with each chromosome consisting of 2 daughter chromatids. If 2 alleles are linked, they will both be situated on a single chromatid, so that they will be inherited together when these chromatids are eventually pulled apart. They will both go to the same daughter cell.
  • Crossing over prevents this.
  • The nearer 2 genes on a chromosome, the lower the chance of a swap occurring between them.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is sex linkage?

e.g. red - green colourblindness

A
  • If he gene that controls it is located on none of the sex chromosomes (X/Y) it will be a sex linked characteristic e.g. occurs when there’s a mutation of the cone pigment genes.
    N - normal
    n = mutant
    parents genotypes: female full colour XnXn
    male XnY
                 XN            Xn XN              XNXn        XNXn

Y XNY XnY

50% full colour girls (25% carriers), 25% full colour boys, 25 %colour blind boys

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Mitosis /Meiosis?
Involves 2 successive nuclear divisions
Does not occur in the production of haploid cells
Involves formation of bivalents
Involves chiasmata formation
Leads to random assortment of chromatids
Leads to random assortment of chromosomes
Occurs during gamete formation in a mammal

A 
Mitsosis     Melosis
                       yes
Yes
                      Yes
                      yes
                      yes
                      yes
                       ye
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Mitosis/meiosis?

  1. Daughter nuclei have identical genetic material
  2. DNA replicated before cell division commences
  3. Involves 2 chromosomal replications
  4. Involved in asexual reproduction
  5. Creates 2 daughter cells
A
  1. Mitosis
  2. Mitosis and meiosis
  3. neither
  4. mitosis
  5. mitosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Mitosis/meiosis?

  1. Creates 4 daughter cells
  2. Involves pairing of homologous chromosomes
  3. Daughter cells have the same chromosome no. as parents cells.
  4. Involves crossing over
  5. Occurs in diploid cels
A
  1. meiosis
  2. meiosis
  3. Mitosis
  4. meiosis
  5. mitosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

i) Name the organelles in a cell which are involved in th synthesis and modification of proteins.
ii) Describe the structure of the bacterial chromosome and explain how it differs from the chromosomes in a eukaryotic cell.

A

i) ribosomes/RER/Golgi

ii) no nucleus
circular
no histories

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

i) What is the only membranous structure inside a prokaryotic cell?
ii) What is an organelle?
iii) RNA must pass through the …..
iv) The DNA in a prokaryotic cell can be found in the … region
v) smallest to largest:
protein organ system organelle organ organism atom tissue cell

A

i) ribosomes
ii) A specialised structur within a cell
iii) nuclear pore
iv) nucleoide
v) Atom - protein - organelle - cell - tissue - organ - organ system - organism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

i) Without piu, what might happen?
ii) True or False. The nuclear envelope contains pores for the passage of large molecules. it’s composed of 2 membranes.
iii) What’s the difference between ‘free’ and ‘attached’ ribosomes?
iv the membrane of the endoplasmic reticulum (ER) are continuous with the membranes of the ……

A

i) the bacterium wouldn’t adhere to other cells as well.
ii True
iii Free - cytoplasm. Attached - anchored to ER
Free- produce proteins in the cytosol.
Attached - produce proteins that’re inserted into the ER.
iv nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

A) What is a mutation?

B) What is independent assortment?

A

A) A random change in either sequence or structure of the DNA.
B) in meiosis each pair of homologous chromosomes lines up on the equator during the first stage of meiosis in one of many (2) possible orientations. The orientation is random.
Therefore its random which on of the homologous pairs of chromosomes ends up in the haploid cells.
(There is a diagram to go with this in your cards)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Describe the stages:

G1 - S - G2 – M (and back to G1)

A

G1 phase: protein synthesis. Organelles and membranes produced.
S phase: synthesis. New DNA is formed
G2 phase: More protein synthesis occurs. Organelles and membranes produced.
Mitosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Interphase

prophase

A

Interphase:
- The cell is engaged in metabolic activity and performing its duty as part of a tissue.
- The DNA duplicates during interphase to prepare for meiosis
- Chromosomes aren’t clearly visible in the nucleus, although the nucleolus maybe visible.
Prophase:
- Chromatin in the nucleus begins to condense an becomes visible in the light microscope as chromosomes.
- The nuclear membrane dissolves
- Microtubules attach at the centromeres and the chromosomes begin moving.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Metaphase

Anaphase

A

Metaphase
- The chromosomes align along the equator of the ell nucleus
- The organisation helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chomosome.
Anaphase:
- The sister chromatids separate at the centromeres and move to opposite sides of the cell (poles).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Telophase

Cytokinesis

A

Telophase:
- New membranes form around the daughter nuuclei.
- Chromosomes disperse and are no longer visible under the light microscope.
Cytokinesis:
- The division of the cytoplasm into two.
- completion of division
- 2 new cells are produced.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Why is mitosis so important?

A
  • ensures genetic consistency with daughter cells, genetically identical to parent cells.
  • Growth and repair: also allows damaged cells to be replaced by identical new ones.
  • Asexual reproduction: The organism creates copies of itself.
  • Prokaryotes don’t carry out mitosis/meiosis - they carry out binary fission, one cell splits into 2 identical cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What are stem cells? (in short)

A
  • Immature cells that can develop into types of tissue
  • Adult stem cells - these are unspecialised cells that can develop into many (but not all) types of cells.
  • Embryonic stem cells - these are unspecialized cells that can develop into any type of cell..
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is meant by the word TOTIPOTENT?

A
  • After human cygote has undergone 3 complete cell cycles it consists of 8 identical cells - each is said to be totipotent as it can develop into a complete human being.
  • Totipotent - they have the potential to develop into a total huma being.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What are blasocysts an pluripotent embryonic stem cells?

A
  • A hollow ball of cells the blastocyst, 5 day old embryo forms. Contains about 100 stem cells. The outer layer goes on to form the placenta. The inner cells form the tissues of the developing embryo.
  • Inner cells are known a pluripotent embryonic stem cell. - each can potentially rise into most cell types - but not all 216 different cell types in the adult human. - ‘pluri’ - plural - many cell types but not all like the ‘totipotents’.
35
Q

What are adult stem cells? (multipotent)

A
  • As the embryo develops only some cells retain a certain capacity to rise to a variety of cell types - known as multipotent stem cells (adult stem cells).
  • Adult stem cells can only produce one type of specialised cell in the area of the body thy’re found. e.g. neural stem cells can develop into various types of cell found in the nervous system. e.g. white blood stem cells,located in bone marrow, can develop into red blood cells, platelets and various sorts of white blood cells.
36
Q

How can embryonic stem cells be used?

therapeutic cloning

A
  • They can be harvested - we can use discarded embryos from fertility treatments (controversial). They can be controlled in the lab to form a specialised cell of the scientists choosing which is then altered or implanted into a patient with an illness.
  • repair organs - transplantations
  • Therapeutic cloning - one of patients diploid cells removed. the nucleus/cell would be fused with an ovum from which the haploid nucleus had been removed - result in a diploid ell rather like a zygote. process known as somatic cell nuclear transfer. A somatic cell is any diploid body cell . This process can be stimulated - mitosis - blasocyst - stem cells - organs.
37
Q

How can adult stem cells be used?

A
  • bone marrow transplants - for leukaemia - adult stem cells move into patient’s bone marrow and produce healthy blood cells.
  • Injections of stem cells to replace damaged brain neurons. cartilage - arthritus.
  • There ha been new developments in the research of prorgramming somatic cells.
38
Q

What is Wilmut’s cloning experiment.

Dolly the sheep

A

Mammary cell donor sheep egg cell donor sheep

mammary cells grown in egg cell from ovary
culture (nucleus removed)

                                      cells fused

nucleus from mammary cell inside egg cell minus its
nucleus

                            grown in culture
                             early embryo

                       implanted 3rd sheep
                         surrogate mother

                          embryo develops lamb 'Dolly' chromosomally identical to mammary cell donor
39
Q

What work did Igor Dawid and Thomas Sargent do on gene expression?

A
  • They demonstrated that different genes are expressed in diff. cells.
  • They extracted (mRNA) from undifferentiated and differentiated frog cells. Complementary DNA (cDNA) strands were produced for all the mRNA in the differentiated cells using anenzyme called transcriptase (reverses transcription - mRNA - DNA).
  • DNA strands mixed with mRNA from the undiff. cell.
  • complementary strands of cDNA and mRN combined to produce double strand hybrids.
  • When hybrids were separated out, a range of cDNA strands that hadn’t been hybridised remained: the 2 cells were expressing some of the same genes - but some are diff. genes.
40
Q

What is the role of the epigenome?

A

Epigenome: influences which genes can be transcribed in particular cell. DNA is wrapped around histone proteins ad both the DNA and histones have chemical markers attached to their surface. These chem. makers make up the epigenome.

  • The attachments (e.g. -CH3) to DNA of a gene prevents transcription to mRNA, by stopping the RNA polymerase binding. Modification of histones (e.g. +-CH3) affects how tightly DNA is wrapped around the histone - when tight - genes are inactive (can’t be transcribed to mRNA) - can’t make protein - ‘switched off’.
  • During DNA replication the epigenetic markers are copied with the DNA - the correct set of gens remain active.
41
Q

What is the Genome?

A

All the DNA inside a cell. The genome contains a full set of all the genes controlling the growth and development of the organism of which the cell is a part.

42
Q

What are transcription factors?

A

Proteins that are involved in switching genes on/off. Transcription factors bind to DNA and control the process of transcription. Some T factors halt the process by blocking the action of the enzyme RNA polymerase. Others activate transcription by promoting the action of the enzyme.

43
Q

When gene expression goes wrong.

What causes FOP?

A

FOP: an inherited condition caused by gene mutation. It’s the growth of bones in odd places.
e.g. bone cells. Normally just produced in growing limbs and where skeleton develops. With FOP, one of these genes not switched off in white blood cells. When tissues damaged - they move to the site. White cells produce the protein - diffuses into muscle cells. Protein causes cells to start expressing other genes that turn them into bone cells.

44
Q

Describe the process of crossing over:

A

A junction is created where one chromatid breaks and rejoins with the other chromatid.
This occurs at random positions anywhere along the chromosomes. There can be one or several crossing over events in each bivalent.
The points at which the chromosomes cross over are called chiasmata (s.chiasma). They are essential for the pairing of the homologous chromosomes and stabilizing the bivalent, as well as being sites of crossing over.

45
Q

Describe each stage of meiosis:

A

Interphase- chromosomes replicating but not yet visible (not strictly part of meiosis)
Prophase1- chromosomes shorten and become visible-homologous chromosomes arrange in pairs (bivalents). Nuclear membrane will break down soon. Spindle fibers start to form.
Metaphase1- spindle fibers attach, homologous pairs of chromosomes line up (randomly) on equator of spindle.
Anaphase1- homologous chromosomes separating.
Telophase1- 2 daughter haploid nuclei formed. The chromosomes will decondense at the end of this phase.
Cytokinesis1- cytoplasm divides. The following interphase is short with no DNA replication.
Prophase2- chromosomes become visible again. New spindle fibers form.
Metaphase2- individual chromosomes line up on new spindles.
Anaphase2- centromeres separate and chromatids move to opposite poles.
Telophase2- 4 haploid nuclei formed.
Cytokinesis2- cytoplasm leaves to form 4 separate haploid gametes.

46
Q

Describe the process of the production of proteins and their root through the cell:

A

mRNA copy of the instructions (gene) is made in the nucleus- mRNA leaves the nucleus through a nuclear pore- mRNA attaches to a ribosome (in this e.g. on RER) which reads the instructions and assembles the protein.
Protein moves through ER assuming 3D shape en-route- protein molecule is ‘pinched off’ in vesicles and travels towards the Golgi apparatus- vesicles fuse with Golgi apparatus- Golgi apparatus processes and packages protein for release.
Packaged protein molecules are pinched off in vesicles and move towards the cell membrane- vesicles fuse with cell surface membrane- cell surface membrane opens to release protein- exocytosis!

47
Q

Switching on an individual gene:

Describe the lac operon model

A
  • Jacob and Monod studied a bacteria that only produced the enzyme beta-galactosidase to break down the carbohydrate lactose.- it converts the disaccharide lactose to monosaccharides glucose and galactose.
  • When lactose is not present- lactose repressor molecule binds to DNA and prevents transcription of beta-galactose date gene.- RNA polymerase can’t bind to DNA promoter region.
  • When lactose is present- binds to repressor- repressor prevented from binding to DNA and beta-galactosidase gene is expressed. mRNA coding for beta-galactosidase is transcribed and translation of this mRNA produces the enzyme.
  • The operator and genes associated with it are known as the OPERON- (lac operon)
48
Q

How are cells organized into tissues?

A

Cells have recognition proteins (adhesion molecules) on their cell surface membrane. These recognize similar cells- stick together small part of each recognition proteins is embedded in cell surface membrane; larger parts extends from membrane- binds to complementary proteins on adjacent cells.
In human embryo this process starts- recognition proteins switched on. In tissues cells also interact with the extracellular matrix- a network of molecules secreted by cells.

49
Q

Describe gene and expression and development:

  • Master genes &
  • The ABC of plants
A

Master genes- control development of each segment.
-produce mRNA that’s translated into signal proteins.
-switch on genes responsible for producing the proteins needed for specialization of cells in each segment.
The ABC of plants:
-4 sets of floral organs arranged in concentric whorls.
-Flowering of Arabidopsis thaliana is used as a model to show what happen when plants change from vegetative growth- reproductive development.

50
Q

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

A
  • Genes in uncoiled, accessible regions of DNA can be transcribed-enzyme RNA polymerase binds to a section of the DNA adjacent to the gene to be transcribed-section known as promoter region-enzyme must attach to DNA to transcribe. Gene remains switched off until the enzyme attaches to the promoter region successfully attachment of a regulator protein is usually required to start transcription.
  • Transcription of a gene can be prevented by promoter repressor molecules attaching to the DNA of the promoter region-blocking attachment site-or/& protein repressor molecules can attach to regulator proteins themselves- preventing them from attaching- genes is switched off.
51
Q

Describe the process of fertilisation:

A
  1. Sperm reach the ovum/ 2. Chemicals are released from the cells surrounding the ovum, triggering the acrosome reaction/ 3. The acrosome swells, fusing with the sperm cell surface membrane/ 4. Digestive enzymes in the acrosome are released/ 5. The enzymes digest through the follicle cells… 6. and the zona pellucida surrounding the ovum-acrosome reaction/ 7. The sperm fuses with the ovum membrane/ 8. The sperm nucleus enters the ovum/ 9. Enzymes released from lysosomes in the ovum thicken the jelly-like layer, preventing entry of other sperm- cortical reaction/ 10. Nuclei of the ovum and sperm fuse.
52
Q

Sperm

A

Acrosome head (5um), tail up to 50um
Flagellum powered by energy released by mitochondrion.
No cytoplasm
Acrosome releases digestive lysosomes to digest zona pellucida
Millions are produce each day-4 per complete meiosis

53
Q

Ovum

A

Cytoplasm (haploid nucleus, lysosomes and lipid droplets), then the cell surface membrane, then jelly-like coating (zona pellucida) then follicle cells from ovary.
0.1mm (100-200um)
Has fatty deposits and other nutrients that are needed during the early stages of development.
Cilia waft it through the oviduct (no independent movement.
400,000 produced at birth/ one per complete meiosis

54
Q

What is discontinuous variation?

A

They have phenotypes that fall into discrete groups with no overlap.

e. g. garden pea plant height.
e. g. blood group (A,B,AB, or O) controlled by genes they inherit, at a single locus. The genes code for glycoprotein on the surface of their red blood cells.

55
Q

What is continuous variation?

A

Characteristics affected by both genotype and environment. e.g. human height.
They are controlled by genes at many loci, known as polygenic inheritance. They are also controlled by the environment either directly or by influencing gene expression.

56
Q

Polygenic inheritance

A

When a number of genes are involved in the inheritance of a characteristic, not just one.

57
Q

Monohybrid inheritance

A

each locus is responsible for a different heritable feature. e.g.one for flower colour and another gene coding for petal shape.

58
Q

Multifactorial conditions

A

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

59
Q

How does polygenic inheritance work?

A

e.g. eye colour
alleles at several loci control eye colour, depends on the amount of pigment in the iris. Pigment absorbs light so brown eyes appear dark, blue eyes have little pigment, light reflect of the iris. A range of possible genotypes are possible according to how many alleles add brown pigment. (BBBBBB or bbbbbb).
e.g. height
The greater the number of loci, the greater the number of classes and the smaller the difference between classes.
Bell-shaped curve when plotted like in continuous variation. environment has an influence, genotype gives their potential height.

60
Q

Why has average height increased over the past 150 years?

A
  • some evidence shows that taller men have more children.
  • greater movements-less inbreeding.
  • Better nutrition-protein.
  • improved health.
  • end of child labour-more energy for growth.
  • better heating in houses in clothes-less energy required to heat the body.
61
Q

How is melanin made?

A

Melanin is dark pigment in skin and hair. Made in special cells, melanocytes, found in skin and at root of hair in the follicle.
Melanocytes activated by melanocyte-stimulating hormones (MSH). On surface of melanocyte cells there are MSH receptors.
Melanocytes place melanin into organelles called melanosomes which are transferred to nearby skin and hair cells where they collect around the skin and hair- more protection against sun burn.

62
Q

How does UV increase the amount of MSH and MSH receptors and what does this do?

A

Makes the melanocytes more active- causing skin to darken.
Hair does not appear darker because although more melanin is produced, UV light causes chemical and physical changes to melanin and other proteins in hair cells. Hair lightens due to destruction of the melanin by UV light.

63
Q

How can arctic foxes change the colour of their coat?

A

They have brown fur (which contains melanin) in the summer and white fur in the winter.
The white winter coat is grown in the summer under the brown coat and is revealed when the fox moults in autumn. The foxes produce fewer MSH receptors in the summer. Without these receptors, MSH has no effect and no melanin is made in the hair follicles.

64
Q

How do animals make melanin and why do come have darker or white tips?

A

Animals use the enzyme Tyrosinase to make melanin. Tyrosinase catalyses the first step along a chemical pathway, changing the amino acid Tyrosinase into melanin.
Animal such as the Himalayan rabbit and the Siamese cat have mutant alleles for Tyrosinase.
The enzyme is made but it is unstable and is inactivated at normal body temperature. However, the tips of their tail, paws and ears are much darker than the rest of their bodies.

65
Q

What is the epigenome?

A

a subset of genes whose function is controlled by specific biochemical factors as well as by their DNA sequence

66
Q

Environmental factors can trigger changes in the epigenome.

2 mice, 1 healthy brown and one obese yellow, describe their differences with reference to the agouti gene.

A

The mice may be genetically identical but epigenetically different. The agouti gene in the healthy brown mouse is methylated and so not expressed but in the yellow, obese mouse it is not methylated and so is expressed.
The agouti gene binds to the MSH receptors in the skin and prevents the production of the dark pigment, it’s also been found that the mouse brain has similar receptors in the area of the brain for feeding behaviour: block these receptors and they may over eat. However, if a pregnant yellow mouse is fed a methyl-rich diet, her young will be slim and brown, suggesting that the epigenetic change is early in development.

67
Q

Behaviour causes epigenetic changes.

Use the Good, Bad rat mother experiment to explain.

A

Rats-Good mothers ( licked and groomed offspring a lot) and bad mothers- there offspring grew up v. similar to them. Switch around the offspring, good mother with bad mother offspring, offspring grow up to be like adoptive mothers.
The GR gene in pups with bad mothers traits has been switched off due to methylation of the gene. Gene produces receptor protein that binds the stress hormone glucocorticoid- when enough has bound, it stops the stress response by causing calming signals to be sent out, relaxing pup after stress.
If there are low levels of the GR protein, hormone levels remain higher in the blood and the pup or adult rat is stresses for longer.

68
Q

What is DNA methylation?

A

DNA methylation is a process by which methyl groups are added to DNA. Methylation modifies the function of the DNA.

69
Q

Can the epigenetic changes be inherited?

A

It is thought that some change pass from parent to child. And that the mothers nutritional well-being at the time of conception can change how her child’s genes will be inherited.
Experiment in Gambia: Mothers pregnant in rainy season, better diets, their infants were found to have more methylation in six of their genes.

70
Q

What causes cancer?

A

Occurs when rate of cell multiplication is faster than rate of cell death- causing tumour growth, often in tissues w/ high rate of mitosis, e.g. lung, bowel, gut and bone marrow.
Cause by DNA damage. By physical factors, e.g. UV and asbestos. By chemicals, e.g. carcinogens in environment or produced by cell metabolism.
If DNA is copied incorrectly in gamete formation, inherited form of cancer can result.

71
Q

How can epigenetic changes cause cancer?

A

Research show that epigenetic changes to DNA and histones have significant role in cancer development. Abnormal methylation of genes that’re involved in the control of the cell cycle. e.g. lower levels of methylation than in healthy cells could cause activation of genes that promote cell division.

72
Q

How does mitosis move from stage to the next?

A

It is controlled. Proteins are produced during each stage of the cycle that stimulate the next stage in the cycle. Cells also produce proteins that stop the cell cycle, preventing progress form stage of the cycle to the next. These proteins activate or inhibit enzymes that initiate the reactions in the next stage of the cycle.

73
Q

Development of cancer:

The control of mitosis and why cancer cells do not respond.

A

Cancer cells do not respond to the control mechanisms that move mitosis from stage to the next. 2 types of gene have a role in control of the cell cycle and play a part in triggering cancer:
1) oncogenes
and 2) tumour suppressor genes.
There needs to be damage to more than one part of the cell control system for cancer to occur- more frequent in older people as they have accumulated more mutations.

74
Q

What are oncogenes?

A

Oncogenes code for the proteins that stimulate the transition from one stage in the cell cycle to the next. DNA mutations or epigenetic changes, e.g. less methylation, in these genes can lead to the cell cycle being continually active. Which may cause excessive cell division, resulting in a tumour.

75
Q

What are tumour suppressor genes?

A

They produce suppressor proteins that stop the cell cycle. DNA mutations or epigenetic changes e.g. more methylation inactivating these genes- mean there is no brake on the cell cycle. Loss of tumour suppressor protein has been linked to skin, colon, bladder and breast cancer.

76
Q

One example of a tumour suppressor protein is p53. Describe what this does:

A

This protein stops the cell cycle by inhibiting the enzymes at the G1/S transition, preventing the cell from copying its DNA. In cancer cells, a lack of p53 means the cell cannot stop entry into the S phase. Such cells have lost the control of the cell cycle.

77
Q

How can smoking cause cancer?

A

Smoking especially increases the risk of lung cancer due to carcinogens in tar. Tar lodges in the bronchi and causes damage to DNA in the surrounding epithelial cells.

78
Q

How can UV light cause cancer?

A

It physically damages DNA in skin cells. Sometimes, a mole that has been affected by UV can get bigger and develop into a tumour. If a tumour isn’t removed, cancer cells sometimes spread to other parts of the body, carried in the blood or lymphatic systems.

79
Q

How can diet and radicals cause cancer?

A

A diet with lots of fruit and veg provides antioxidants that destroy radicals.
Radicals are from chemicals in diet or environment, smoke and UV or produced by a persons own metabolism. Radicals contribute to ageing and cancer through DNA damage.

80
Q

How can virus infections cause cancer?

A

Several cancers are triggered by virus infection. e.g. liver cancer can follow some types of hepatitis, and cervical cancer can follow infection by the papilloma (genital wart) virus. A virus’s RNA may even contain an oncogene, which it has picked up from one of its hosts and then transfers to the cells it infects.

81
Q

How to combat cancer?

A

Surgery to remove tumour.
Chemotherapy- use of chemicals to destroy cancer cells.
Radiotherapy X-rays/ other radiation.
Radiotherapy and chemotherapy thought to work by inducing cells to carry out cell suicide.

82
Q

What is the role of the cell cycle?

A
  • Growth and repair

- Asexual reproduction

83
Q

Where is mRNA synthesised in a eukaryotic cell?

A

The nucleus

84
Q

Describe an experiment that could be carried out to investigate the effect of enzyme concentration on the initial rate of reaction:

A
  • Range of conc. of enzymes.
  • idea of substrate concentration not limiting.
  • ref. to mixing
  • dependent variable
  • measure initial rate
  • controlled variables
  • repeats
  • control as a comparison

Biology A level (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions