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Biology Extras > Advanced Notice Article > Flashcards

Advanced Notice Article Flashcards

1
Q

What is melanogenesis

A
  • Formation of melanin
  • Oxidation of amino acid tyrosine
  • Followed by polymerisation of different molecules
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2
Q

Where is melanin found?

A
  • Keratinocytes (skin cells)
  • Hair
  • Cells under iris
  • Medulla oblongata
  • Part of ear
  • Part of adrenal gland
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3
Q

What are melanosomes?

A
  • Organelle found in animal cells
  • Site for synthesis, storage and transport of melanin
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4
Q

What is melanin?

A
  • Dark pigment found in melanocytes
  • Most common light-absorbing pigment found in animal kingdom
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5
Q

What is tyrosine?

A
  • Non-essential amino acid
  • Has polar R group BUT is considered hydrophobic
  • Coded for by UAC or UAU in mRNA
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6
Q

How does tyrosine form melanin?

A
  • Tyrosine oxidised to DOPA by enzyme tyrosinase
  • DOPA converted to dopaquinone by enzyme tyrosinase
  • Dopaquinone converted to melanin
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7
Q

What is the importance of tyrosinase?

A
  • TYR gene on chromosome 11 codes for enzyme tyrosinase
  • Recessive allele for gene TYR = lack or tyrosinase OR presence of inactive tyrosinase
  • No tyrosinase enzyme = tyrosine not converted to melanin
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8
Q

What else can tyrosine be converted to?

A
  • Tyrosine converted to DOPA and then to melanin
  • BUT DOPA an also be converted to noradrenaline and adrenaline
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9
Q

Where are melanocytes found?

A
  • Melanocytes are cells in skin and eyes
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10
Q

What is the choroid?

A
  • Thin layer of tissue between sclera and retina
  • Richly supplied with blood vessels = supply oxygen and nutrients to retina
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11
Q

What is the function of pigmented epithelium in choroid?

A
  • PIGMENTED EPITHELIUM = Inner layer of choroid = layer of cells containing melanin
  • Absorbs any light that passes through rods and cones so it is not reflected back into eye
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12
Q

What is the uveal tract?

A
  • Consists of choroid, ciliary body and iris
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13
Q

What are the functions of the uveal tract?

A
  • Reduced reflected light within eye = improves contract of retinal image
  • Absorbs outside light transmitted through sclera (not fully opaque)
  • Secreted aqueous humour from ciliary processed
  • Controls accommodation via ciliary body (autonomic nervous system)
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14
Q

What else does the uveal tract consist of?

A
  • Immune cells (particularly lymphocytes)
  • Responds to inflammation by developing lymphatic infiltrates
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15
Q

What is sympathetic ophthalmia?

A
  • Rare disease
  • Body unable to distinguish between uveal and retinal antigens
  • SO misdirected inflammatory reactions
  • SO auto-immune response
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16
Q

What are uveal melanocytes?

A
  • Pigmented cells which form part of uvea
  • Contribute to eye colour phenotypes
  • Can develop rare type of eye cancer
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17
Q

What is the effect of UV radiation on human skin?

A
  • exposure to UV radiation initiates melanogenesis = skin darkens
  • One form of melanin dissipates over 99.9% of absorbed UV radiation
    = protects skin cells from UVA and UVB radiation damage

= reduced risk of folate depletion and dermal degradation

  • More concentrated melanin (darker skin tone) = lower incidence of malignant melanoma
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18
Q

What is oxidative stress?

A
  • Damage to cell structures can be due to increased conc of certain chemicals

(e.g.: hydrogen peroxide = waste product of respiration)

  • Environmental stress (UV/heat exposure) = dramatic increase in levels of hydrogen peroxide and other chemicals
  • Cumulative effect = oxidative stress
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19
Q

What does melanin protect against?

A
  • Protects microorganisms (fungi, bacteria) against stresses involving cell damage (UV radiation from sun, hydrogen peroxide)
  • Protects against damage from high temps
  • Protects against chemical stresses (heavy metals, oxidising agents)
  • Protects against biochemical threats (host defences against invading microbes)
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20
Q

What is immune regulation?

A
  • Suppression or stimulation of the immune system
  • Occurs through gene expression of immune genes
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21
Q

How does immune system distinguish between self and non-self antigens?

A
  • Distinguish between self + non self antigens
  • Distinguish between harmful + innocuous foreign antigens
  • Deletion of self-reactive clones in thymus (negative selection) = prevents auto-immune responses
  • Melanocytes form proteins that can suppress or enhance immune system
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22
Q

What is angiogenesis?

A
  • Angiogenesis = formation of new blood vessels
  • New blood vessels develop from existing cells
  • Melanocytes can stimulate angiogenesis
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23
Q

What is the importance of angiogenesis?

A
  • Process slows in adulthood (but ability to grow new blood vessels is retained)
  • Essential for tissue growth and normal development (e.g.: pregnancy, puberty)
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24
Q

List the electromagnetic spectrum, low to high frequency

A
  • Radio waves
  • Microwaves
  • Infrared
  • Visible Light
  • Ultraviolet
  • X-rays
  • Gamma rays
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25
Q

What are pigment granules?

A
  • Small, sub cellular membrane-bound vesicle
  • Contains pigment and/or pigment precursor molecules
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26
Q

Where are pigment granules formed?

A
  • Multiple sources, including:
  • endoplasmic reticulum
  • coated vesicles
  • lysosomes
  • endosomes
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27
Q

What happens to melanin when exposed to UV light?

A
  • Melanocytes form temporary pseudopodia = carry melanosomes from centre of cell to edge of cell
  • increases cells effectiveness at absorbing light
  • process occurs slowly in response to exposure to UV light
  • UV light = new melanosomes produced
  • Transferred to adjacent keratinocytes in skin
  • Melanocytes position themselves by nucleus, closest to UV light = protects genetic material against harmful effects of UV radiation
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28
Q

What is circular tissue?

A
  • Radial and circular muscles (antagonistic muscles)
  • Control the diameter of the pupil
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29
Q

How are radial muscles stimulated?

A
  • Stimulated by sympathetic nervous system
  • SNV usually increases activity (fight, fright, flight)
  • Post ganglionic NT = noradrenaline
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30
Q

How are circular muscles stimulated?

A
  • Stimulated by parasympathetic nervous system
  • PNS usually decreases activity (rest and digest)
  • Post ganglionic NT = acetylcholine
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31
Q

What is a phenotype?

A
  • The physical observable characteristics that are expressed in an organism
  • Affected by both genotype and environment
  • Includes biochemistry, physiology, morphology and behaviour
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32
Q

What is a genotype?

A
  • The combination of alleles present in a cell or organism
  • Heterozygous, homozygous recessive or homozygous dominant
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33
Q

What is a polygenic characteristic?

A
  • Controlled by several genes
  • Usually show continuous variation (e.g.: height, mass, skin colour)
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34
Q

What is epigenetic modification?

A
  • Organisms internal or external environment can influence gene expression patterns
  • Levels or regulatory proteins or transcription factors affected in response to environmental stimuli (light, chemicals, drugs, hormones)
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35
Q

How is melanin production altered by epigenetics?

A
  • Some enzymes are activated in response to UV radiation
  • enzymes increase expression of melanin-producing genes
  • therefore increase production of melanin
  • leads to skin pigmentation
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36
Q

What causes the transport of melanin?

A
  • Cytophagocytosis
  • Direct Membrane Fusion
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37
Q

How does cytophagocytosis cause the transport of melanin?

A
  • A melanocyte dendrite is phagocytosed
  • Forms a phagolysosome
  • Melanin granules disperse from phagolysosome through the cytoplasm of keratinocytes
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38
Q

How does Direct Membrane Fusion cause the transport of melanin?

A
  • Plasma membranes of both cells fuse
  • Creates a nanotube which allows the passage of melanosomes
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39
Q

What features do homologous chromosomes share?

A
  • Biochemical structure (i.e. DNA)
  • Physical shape and size
  • Sequence of genes
  • Gene loci
  • Centromere position
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40
Q

What features differ between homologous chromosomes?

A
  • Different origins (one maternal, one paternal)
  • Different alleles
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41
Q

What is a gene loci?

A

Position of a gene on a chromosome

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42
Q

What is Oculocutaneous albinism?

A
  • A form of albinism involving eyes, skin and hair
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43
Q

What are the general causes of Oculocutaneous albinism?

A
  • Caused by mutations in several genes (polygenic) that control synthesis of melanin within melanocytes
  • Seven types of Oculocutaneous albinism described
  • All caused by disruption of melanin synthesis
  • All autosomal recessive disorders
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44
Q

What are the causes of Oculocutaneous albinism in humans?

A
  • In humans, OCA2 gene located on long arm of chromosome 15
  • Most common type of albinism caused by mutation of P gene
  • Mutations in OCA2 cause type 2 Oculocutaneous albinism
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45
Q

What are the effects in humans of Oculocutaneous albinism?

A
  • OCA2 codes for human equivalent of mouse p (pink-eyed) gene
  • People with OCA2 usually have fair skin
  • Usually pale blonde to golden, strawberry blonde or even brown hair
  • Usually blue eyes
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46
Q

What are the effects in people of African descent with Oculocutaneous albinism?

A
  • Yellow hair
  • Pale skin
  • Blue, grey, hazel eyes
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47
Q

What is P protein and where is it found?

A
  • Coded for by OCA2, pigment can develop in freckles or moles
  • Also known as melanocyte-specific transporter protein OR pink-eyed dilution protein
  • Found in melanocytes and retinal pigmented epithelium
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48
Q

What is the function of P protein?

A
  • intrinsic membrane protein
  • Involved in transport of tyrosine into melanocytes
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49
Q

What is HERC2?

A
  • A protein ligase involved in DNA repair regulation
  • Protein ligases important in cell cycle control, controlling breakdown of cyclins and CDK inhibitor proteins
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50
Q

How does HERC2 determine iris pigmentation?

A
  • Mutation in HERC2 gene adjacent to OCA2 = affects OCA2’s expression in iris
  • Common to nearly all people with blue eyes
  • Are 15 single nucleotide polymorphic forms of HERC2 gene (germline single DNA-nucleotide substitutions) which determine iris pigmentation
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51
Q

How do you calculate proportion of polymorphic gene loci?

A

number of polymorphic gene loci
______________________________________
total number of loci

(no units as is a ratio)

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52
Q

What are introns?

A
  • Large regions of non-coding DNA which are removed from pre-mRNA before it is translated
  • Removed during post-transcription modification (occurs in nucleoplasm = converts pre-mRNA to mature mRNA)
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53
Q

What are the steps of gene expression?

A
  • Transcription
  • Post transcription modification
  • RNA splicing
  • Translation
  • Post translation modification
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54
Q

Why are steps in gene expression controlled?

A
  • Ensures genes are only expressed when are where required for required duration
  • Determines cell differentiation, organism development and adaptability of organism
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55
Q

What are some important examples of gene expression?

A
  • Control of insulin expression (blood plasma glucose regulation)
  • Control of cyclin expression in eukaryotic cell cycle
  • Control achieved by DNA methylation and histone coat modification
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56
Q

What are barrier tissues?

A
  • Epithelial and epidermal barriers protect the body from pathogens and from other environmental stresses
  • Also separate different internal organs with a unique cellular structure and chemical composition
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57
Q

Name a barrier tissue that protects body from pathogens and environmental stresses

A

CILIATED EPITHELIUM

  • specialised tissue that lines airways
  • Small projections (cilia) sweep mucus, dust and bacteria upwards and away from the lungs with the epithelium itself
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58
Q

Name a barrier tissue that separates different internal organs

A

EPITHELIUM

  • A type of body tissues
  • Forms the covering on all internal and external surfaces of the body
  • Lines body cavities and hollow organs
  • Is the major tissue in glands
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59
Q

What are mucous membranes?

A
  • Line the gut, airways and reproductive system
  • Consists of epithelial cells and mucus-secreting goblet cells
  • Contains lots of glycoproteins with long carbohydrate chains (glycocalyces) such as mucin
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60
Q

What is the function of mucus?

A
  • Mucus in trachea, bronchi and bronchioles traps inhaled viruses, bacteria, pollen and dust
  • Particles moved towards back of throat by wafting of cilia
  • Mucus and trapped particles swallowed or expelled by coughing up mucus
  • Ciliated epithelial cells have motile cilia = beat and move in wave-like manner = moves mucus along airway
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61
Q

Outline the role of phagocytes

A
  • WBC produced continuously in bone marrow
  • Remove dead cells and invasive microorganisms (non-specific immune response)
  • Move in amoeboid movement to site of infection and attach to pathogens
  • CSM of phagocyte extends out and around pathogen = forms pseudopodia = engulfs it by endocytosis
  • Phagosome fuses with lysosome = phagolysosome

= Hydrolytic enzymes from lysosome digest pathogen = hydrolysis reactions of biochemical components of pathogen)

62
Q

Outline the role of T lymphocytes

A
  • T cells activated when encounter and bind to specific antigen on surface of antigen-presenting cell (clonal selection)
  • APC = macrophage, infected body cell or pathogen itself
  • Activated T cells divide by mitosis (clonal expansion) = increase in number = genetically identical daughter cells
  • Activates T-helper cells bind with complementary receptors on surface membrane of specific B-lymphocytes
  • On binding, T-helper cells release signalling proteins = activate B lymphocytes
63
Q

Outline the role of T helper cells

A

Release cytokines (hormone-like signals) to stimulate:

  • Maturation of B-lymphocytes into plasma B-cells
  • Production of memory B cells
  • Activation of cytotoxic T cells
  • Increased rate of phagocytosis
64
Q

Outline the role of T killer cells

A
  • Patrol body in search of APCs
  • Attach to foreign substances on cam of infected cells
  • Secrete toxic substances = kill infected body cells and pathogen inside
  • Perforins secreted by T killer cells punch hole in csm of infected cells = toxins enter
65
Q

Outline the role of B lymphocytes

A
  • B lymphocytes with correct cell surface antibodies recognise antigen and bind to it (clonal selection)
  • Binding –> antigen-antibody complex
  • Bdining along with cell signalling molecules produced by T helper cells activates B lymphocyte
  • Activated = B cells divide repeatedly by mitosis = produces many clones of original activates B cell (clonal expansion)
66
Q

What are the two main types of B cell?

A
  • Effector cells = differentiate into plasma cells = produce specific antibodies to combat non-self antigens
  • Memory cells = remain in blood = allow faster immune response to same pathogen in future
67
Q

What is the Cornea?

A
  • Layer under conjunctiva, continuous with sclera
  • Focuses light onto retina
  • Main structure responsible for refraction of light rays onto retina
68
Q

What is the inflammatory response?

A
  • Localised response to pathogens at site of wound
  • Result = pain, swelling, heat and redness of tissue
  • Mast cells activated in damaged tissue
  • Mast cells release histamine, cytokines, serotonin and prostaglandins
69
Q

What is the role of histamines in the inflammatory response?

A
  • Make arterioles dilate (vasodilation) = increased blood flow to area
  • localised redness, increased pain sensitivity and heat (higher temp prevents pathogens reproducing)
  • Make arteriole walls more leaky = more plasma forced out = increased tissue fluid formation = soreness, swelling (oedema) and pain
70
Q

What is the role of cytokines in the inflammatory response?

A
  • (e.g.: Interleukin 1 and interleukin 6)
  • Attract phagocytes to wound = phagocytosis = destruction of pathogens
  • Also stimulate liver to release proteins = bind to surface of bacteria and damaged host cells = promote phagocytosis by macrophages
71
Q

What is the role of serotonin and prostaglandins in the inflammatory response?

A
  • Make arterioles dilate and more leaky
  • Some plasma proteins leave blood
72
Q

What is the role of an antigen-presenting cell?

A
  • T lymphocytes produce an immune response when exposed to a specific antigen
  • T lymphocytes only bind to a specific antigen if its present on surface of APC
  • Once surface receptor of T lymphocyte binds to specific complementary antigen on APC it becomes sensitised
  • It starts dividing to produce clones of cells
73
Q

What can be antigen-presenting cells?

A
  • Most common types = macrophages and dendritic cells
  • Less common = neutrophils
74
Q

What is the structure of T-lymphocytes?

A
  • Produced in bone marrow, mature in thymus
  • Mature T cells have specific cell surface receptors - T cell receptors
  • Receptors have similar shape ton antibodies and each is specific to particular type pf antigen
75
Q

What are the 2 types of Herpes Simples Virus (HSV)?

A

Type 1
- Spreads by oral contact
- Causes infections in or around mouth (oral herpes or cold sores)
- Can cause genital herpes
- Most adults infected with HSV-1

Type 2
- Spreads by sexual contact
- Causes genital herpes

76
Q

What is Herpetic Stromal Keratitis (HSK)?

A
  • An intense inflammatory response, triggered by viral infection of corneal stroma
  • If left untreated, chronic inflammatory response –> formation of lesions, scarring and eventually blindness
77
Q

What is the structure of Herpes Simples Virus?

A
  • DNA virus within nucleocapsid
  • Matrix (called the tegument) = made up of proteins and mRNAs = allows virus to evade immune response of host cells and facilitate its replication once its invaded host cells
  • Envelope = lipid bilayer = contains virally encoded glycoprotein spikes = important for viral entry
78
Q

What is the role of glycoproteins on surface of HSV?

A
  • At least 12 types of glycoproteins with diverse shapes/sizes reported on surface of HSV
  • Facilitate viral entry into host cells by interacting with receptors on host cell surface (viral attachment)
  • Glycoproteins also interact with other glycoproteins
  • Glycoproteins fuse viral envelope with host cell membrane = enables delivery of viral content into cell
79
Q

What is the function of the spleen?

A
  • Stores blood )to be released in times of hypovolemic shock)
  • Removes old erythrocytes from circulation
  • Acts in similar way to lymph node = filters blood plasma
  • Contains high number of B-lymphocytes and monocytes
  • Produces all types of blood cells during fatal life
  • Produces opsonins
  • Releases neutrophils following myocardial infarction
  • Involved in recycling of iron from old erythrocytes and breakdown (hydrolysis) of globin chains of Hb
80
Q

What is the structure of lymph capillaries?

A

(Some TF drains into lymph capillaries)

  • Separate from circulatory system
  • Have closed end and large pores = allow large molecules to pass through
  • Larger molecules that cannot pass through capillary wall enter lymphatic system as lymph via small, one-way valves in lymph vessel walls
81
Q

What is the role of lymph?

A
  • Lymph moves along larger lymph vessels due to compression (from skeletal muscles contracting)
  • Valves prevent backflow
  • Lymph re-enters DCS through subclavian vein
  • Any plasma proteins that escaped from blood = returned to blood via lymph capillaries
  • Plasma proteins not removed from TF = lower WP of TF = prevents reabsorption of of water into blood
  • After digestion, lipids transported from intestines to bloodstream by lymph system
82
Q

What happens at the arteriole end in lymph formation?

A
  • Hydrostatic pressure forces small, soluble molecules out of blood in capillary via fenestrations in capillary wall
  • Plasma proteins remain in blood = creates WP between capillary and tissue fluid
  • Overall movement of water = out of capillaries, into tissue fluid
83
Q

What happens at the venue end in lymph formation?

A
  • Hydrostatic pressure in capillary reduced = less liquid forced out of capillary
  • WPG between capillary and tissue fluid remains same as at arteriole end = water begins to flow back into capillary from tissue fluid via osmosis
  • Overall = more fluid leaves capillary than returns = tissue fluid left behind to bathe cells
84
Q

What is the effect of hypertension on lymph fluid formation?

A
  • Pressure at arterial end is greater
  • Forces larger volume of fluid out of capillary
  • Fluid accumulates = causes oedema
85
Q

What is compartmentalisation?

A
  • Occurs in development of specialised cell
  • Enables unicellular organisms to develop specialised functions through specific areas of their cell
  • E.g.: nucleus region contains DNA molecules, compartmentalisation of ATP = produces area formed by endosymbiosis of mitochondria
86
Q

What is the importance of specialisation?

A
  • Enables the cells in a tissue to function more efficiently as they develop specific adaptations for that role
  • Development of distinct specialised features occurs by differentiation
87
Q

What changes occur during differentiation?

A
  • Change in shape of cell
  • Change in organelles the cells does or doesn’t contain
  • Change in chemical composition of cell
    (e.g.: presence or increased conc of a specific protein, such as melanin in melanocyte, mucin in goblet cell, haemoglobin in erythrocyte)
88
Q

Why might T-lymphocytes enter cornea?

A
  • Virus-specific T-lymphocytes enter cornea in significant numbers following HSV infection
  • Memory T-cells remain in cornea after virus was eliminates (likely to ward off future reinfection)
89
Q

What is a tissue?

A
  • A group of similar cells
  • Consisting of one or more than one cell type
  • With any extracellular material they secrete
  • Which are specialised to carry out a specific function
  • e.g.: squamous epithelium, ciliated epithelium, xylem tissue, phloem tissue, nervous tissue
90
Q

Where do T memory cells circulate?

A
  • Plasma
  • Lymph
91
Q

What are virus-specific T-lymphocytes?

A
  • A target therapy generated for specific viral antigens
  • Antigens identified as immune target presented by APCs to T-lymphocytes along with other molecules that stimulate their growth and activation
  • Those T-cells then isolated from donor and expanded in culture to generate more VSTs
  • Some cases = cells created from blood samples of patients who have recovered from viral infections
92
Q

What do the letters stand for in Hardy Weinberg equation?

A

P = frequency of dominant allele

Q = frequency of recessive allele

P^2 = frequency of homozygous dominant genotype

Q^2 = frequency of homozygous recessive genotype

2pq = frequency of heterozygous genotype

93
Q

What is allele frequency?

A

Relative frequency of an allele )variant of a gene) at a particular locus in a population, expressed as a fraction of percentage

94
Q

What is a gene?

A
  • A section of DNA that codes for a single polypeptide chain
95
Q

What determines genotype?

A
  • Phenotypic variation due to combination of genetic and environmental factors
  • e.g.: recessive allele causing sickle cell anaemia = high frequency in populations where malaria present as heterozygous recessive individuals are resistant to malaria
  • Complete phenotype of an organism determined by expression of its genotype and interaction of environment

Phenotype = Genotype + environment

96
Q

How can the environment affect a phenotype?

A
  • Levels of regulatory proteins or transcription factors can change in response to environmental stimuli (e.g.: light, chemicals like drugs and hormones)
  • Some enzymes activates in response to UV radiation = increase expression of melanin-producing genes
97
Q

What are epigenetics?

A
  • Control of gene expression by factors OTHER THAN an individual’s DNA sequence
  • Involves switching on and switching off genes WITHOUT changing the actual genetic code
98
Q

How can chromatin be genetically modified?

A
  • Methylation of DNA = chemical addition of -CH3 groups to the cytosine NCBs
  • Histone modification = Via acetylation of amino acid tails
  • These modifications are called epigenetic tags
99
Q

What is the epigenome?

A
  • All the epigenetic tags in an organism
  • Epigenome can undergo changes due to smoking, stress, exercise ad diet
  • Internal signalling fro, body’s own cells can also cause modifications to occur
  • Epigenetic modification is independent (e.g.: DNA methylation or histone modification in one area is NOT linked to modification in another)
100
Q

What is the effect of winding in epigenetic changes?

A
  • Chemical modification of histones and DNA controls how tightly the DNA is wound around them
    (as intermolecular bonding between histones and DNA changes)
  • DNA wound more tightly in certain area = genes on this section of DNA are ‘switched off’
    (as gene and promoter regions more hidden from transcription factors and RNA polymerase)
  • Histone modification is reversible = can be different in different cell types and can vary with age
101
Q

What is the effect of DNA methylation?

A
  • Methyl groups directly added to DNA to alter gene expression
  • Usually involves direct addition of methyl group to cytosine bases
  • Methylation of DNA suppresses transcription of affected gene by inhibiting binding of transcription factors and enzymes needed for transcription (e.g.: RNA polymerase)
  • Cells use mechanism to lock genes in ‘off’ position = gene repressed / inactivated
  • DNA methylation affected by many environmental, lifestyle or age-related factors
102
Q

What is the effect of lysine in gene expression?

A
  • Acetyl groups added to lysine amino acids on histone proteins
  • Lysine has positively charged R group
  • Forms ionic bonds with negatively charged sugar-phosphate backbone of DNA
  • Helps DNA coil tightly around histone protein core
103
Q

What is the effect of acetylation of histones in gene expression?

A
  • Adding acetyl groups to lysine residues removes positive ion = removes bond between histone protein and DNA
  • SO DNA less tightly wrapped around histones
  • RNA polymerase and transcription factors can bind more easily = gene expression can occur
  • Gene = activated
104
Q

What is the effect of deacetylation on gene expression?

A
  • Removal of acetyl groups
  • Makes lysine return to its [ositively charged state
  • So stronger attraction to DNA molecule
  • So inhibits transcription
  • So stops gene expression
105
Q

Why can epigenetic changes be passed onto daughter cells?

A
  • E.g.: during gamete production - DNA in parent cell underuse de-methylation BUT often methyl groups not removed = present in DNA in sperm of oocytes
  • MAYBE AS epigenetic changes occur in response to environmental factor
    = beneficial for epigenetic changes to also occur in daughter cells (e.g.: gametes)
    = adapted for environmental factor
  • Modifications to epigenome in one generation passed onto next generation at cellular or whole organism level

= Epigenome is heritable

106
Q

Give some examples of membrane proteins

A
  • Receptors (e.g.: hormone receptor such as insulin)
  • Immobilised enzyme (e.g.: maltase)
  • Channel proteins (e.g.: sodium ion channels)
  • Voltage-gated channels (e.g.: potassium ion channels)
  • Electron carriers (e.g.: cytochrome)
  • Carrier-Protein Pump (e.g.: sodium-potassium ion pump)
  • Cell-to-cell recognition (e.g.: glycoprotein-antigen)
  • Anchor proteins
  • Proteins enabling cell adhesion
107
Q

What are the roles of uveal melanocytes?

A
  • Light absorption
  • Regulation of oxidative stress
  • Immune regulation
  • Formation of new blood vessels
108
Q

What rays does melanin absorb?

A
  • Infrared light
  • Visible light
  • Ultraviolet radiation

(in front of eye, melanocytes block 99.9% of these wavelengths)

109
Q

What are the 2 types of melanin?

A
  • Eumelanin (brownish black)
  • Pheomelanin (reddish yellow)
110
Q

Why do amino acids act as buffers?

A
  • Amphoteric = can donate or accept electrons
  • Zwitterion formed (as COO- group or NH3+ group) = can be either positively or negatively charged amino acid
  • Amphoteric and zwitterions = act as buffers as add or remove protons into environmental solution = alter pH
111
Q

General recap of amino acids

A
  • 20 naturally occurring amino acids
  • Amino / Amine group = NH2
  • Carboxyl group = COOH
  • R group (or side chain) varies between amino acids
112
Q

Overview of tyrosine

A
  • Codes for by UAC or UAU in mRNA = example of degenerate codon
  • Recessive allele for tyrosine –> albinism
  • Residual group likely specific for tyrosinase active site
  • R group has ‘OH’ = can form hydrogen bonds
  • R-group is polar = R-group is hydrophilic (but not the amino acid itself)
  • Means tyrosine is soluble in water
113
Q

What is the definition of primary protein structure?

A

Number and sequence of a chain of amino acids joined by a series of condensation reactions, forming peptide bonds

114
Q

What is the definition of secondary protein structure?

A

Local folding of the polypeptide chain into alpha helices and/or beta pleated sheets, held in place by hydrogen bonds

115
Q

What is the definition of tertiary protein structure?

A

Three-dimensional further folding pattern of a polypeptide chain due to residual groups, resulting in a globular or fibrous protein

116
Q

What is the definition of quaternary protein structure?

A

2 or more polypeptide chains, OR 1 polypeptide chain and a prosthetic group

117
Q

Describe the bonds in primary protein structure

A
  • Peptide
  • Covalent (which are peptide bonds)
118
Q

Describe the bonds in secondary protein structure

A
  • Peptide
  • Hydrogen bonds between NH of amino group of one amino acid and C=O of carboxyl group of another amino acid
  • Covalent (which are peptide bonds)
119
Q

How are alpha helices and beta-pleated sheets formed?

A
  • Hydrogen bonds form between NH of amino group in chain and C=O of carboxyl group (usually 4 amino acids further down polypeptide chain)
120
Q

Describe the bonds in tertiary protein structure

A
  • Peptide
  • Additional hydrogen bonds between functional groups which form dipoles in a single ppc
  • Hydrophobic interactions between non-polar R-groups in same ppc
  • Disulphide bonds between 2 cysteine R-groups of same ppc
  • Ionic bonds between polar R-groups of same ppc
  • Covalent (which are peptide bonds)
121
Q

Describe the bonds in quaternary protein structure

A
  • Peptide
  • Hydrogen bonds can form between same ppc or different ppc’s
  • Hydrophobic interactions between non-polar R-groups between same or different ppc’s
  • Disulphide bonds between 2 cysteine R-groups of same or different ppc’s
  • Ionic bonds between polar R-groups in same or different ppc’s
  • Covalent (which are peptide bonds)
122
Q

How does melanocyte show differentiation: Change in number of organelles?

A
  • presence of melanosomes
  • higher number of mitochondria
  • increased RER (size and number) = more extensive and more cisternae
  • Increased number of Golgi apparatus
  • Higher number of 80s ribosomes as is a eukaryotic cell
123
Q

How does melanocyte show differentiation: Change in chemical composition?

A
  • Increased concentration of melanin
  • Higher quantity of mRNA for the melanin
124
Q

How does melanocyte show differentiation: Change in shape

A
  • Extensions / protrusions of csm
  • Projections of cytosol to form dendrites
  • Irregular shape
125
Q

How is a melanosome formed?

A
  • Membrane-bound vesicle containing melanin
  • Buds off Golgi vesicle
126
Q

What is the function of the cornea?

A
  • Protective layer, refracting light rays as they enter the eye
127
Q

What is the function of the iris?

A
  • Consists of radial muscles and circular muscles (antagonistic)
  • Controls intensity of light that passes through pupil

PUPIL REFLEX:
- When pupil constricts, circular muscles contract

  • When pupil dilates, radial muscles contract
128
Q

What is the function of the lens?

A
  • Transparent disc that can change shape to focus light rays on the fovea of the retina
  • Carries out accommodation, controlled by ciliary muscles and suspensory ligaments
129
Q

What is the function of the retina?

A
  • Light rays are refracted onto the retina
  • Contains photoreceptors (rod cells and cone cells) to absorb light
  • Fovea has highest concentration of cone cells
130
Q

What is the function of the optic nerve?

A
  • Collection of neurones that carries nerve impulse between photoreceptors on retina and occipital lobe
131
Q

What is the function of the pupil?

A
  • Point at which light enters eye
  • Constriction or dilation of pupil controlled by radial and circular muscles in iris = pupil reflex = accommodation
132
Q

Outline rod cells

A

Pigment = rhodopsin

Type of vision = black and white

Number of cells that synapse with 1 bipolar neurone = 2 or more (multiple)

Sensitivity to light = higher

Visual acuity = lower

133
Q

Outline cone cells

A

Pigment = iodopsin

Type of vision = colour

Number of cells that synapse with 1 bipolar neurone = 1

Sensitivity to light = lower

Visual acuity = higher

134
Q

What are the different substances that can result in environmental stress?

A
  • UV
  • Heat (damages bonds)
  • Hydrogen peroxide = apoenzyme (needs calcium ions), broken down by catalase
135
Q

Why are gamma rays the most dangerous of the EM waves?

A
  • Highest energy as highest frequency = more likely to cause damage
136
Q

How can a melanosome be transferred from one cell to another?

A

Different types of bulk transport:

  • Phagocytosis (adapted)
  • Spontaneous annealing of membranes (adapted)
  • Endocytosis (adapted)
  • Exocytosis and phagocytosis (adapted)
137
Q

What is bulk transport?

A
  • Active process
  • Uses ATP as cytoskeleton involved
  • More tubulin produced = more protein synthesis needed = more ATP needed
138
Q

What is the definition of a gene?

A

A short length of DNA that codes for the production of a specific polypeptide chain

139
Q

What is the definition of an allele?

A

A gene variant that codes for the variation of the gene

140
Q

What is the definition of a dominant allele?

A

An allele which is always expressed if present in the genotype, as only 1 copy is needed in the genotype to be expressed in the phenotype

141
Q

What is the definition of a recessive allele?

A

An allele that is only expressed in the phenotype if two of them (2 recessive alleles) are present in the genotype

142
Q

What is the definition of genotype?

A

The combination of all alleles present in a cell of individual

143
Q

What is the definition of phenotype?

A

Observable characteristics expressed due to the organism’s genotype

144
Q

What is the definition of homozygous?

A

A genotype made up of 2 alleles of the same type

145
Q

What is the definition of heterozygous?

A

A genotype made up of 2 different alleles, one dominant and one recessive

146
Q

What is the definition of monogenic?

A

A phenotype that is controlled by a single gene

147
Q

What is the definition of polygenic?

A

A phenotype that is controlled by 2 or more genes

148
Q

What is the function of OCA2?

A
  • Gene located on chromosome 15
  • Crucial role in production melanin (especially brown-black eumelanin)
149
Q

What is the effect of mutated OCA2?

A
  • OCA2 gene codes for protein that regulated melanosomes which produce melanin
  • Mutation = affects quantity and distribution of melanin in iris
  • 2 functional copies of OCA2 = brown eyes
  • 2 non-functional copies of OCA2 = blue of green eyes (as less eumelanin produced = underlying blue structural colour more visible)
150
Q

How is HERC2 involved in eye colour?

A
  • Specific region of HERC2 gene regulates expression of OCA2
  • Mutations in HERC2 affect expression of OCA2
  • A variant of HERC2 more common in people with blue eyes

Biology Extras (4 decks)

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