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Biology HL > Molecular biology 2.7, 3.1, 3.2, 3.5, 7.2, 7.3 > Flashcards

Molecular biology 2.7, 3.1, 3.2, 3.5, 7.2, 7.3 Flashcards

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1
Q

What is a gene?

A
  • heritable factor
    • consists of a length of DNA
    • influences a characteristic
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2
Q

What is an allele?

A

> one specific form of a gene
occupy the same locus in different specimens
differ by one (SNPs) or a few bases
formation of new alleles
- point mutation - change of one or some bases within a gene
- substitution (most common), insertion, deletion, inversion
- silence: no change, missense: different, nonsense: no protein

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3
Q

What is the structure of haemoglobin?

A
  • protein blood (red)
  • 4 polypeptide chains
    • 2 alpha and 2 beta
    • ring-like heme (with Fe)
  • oxygen binds to iron
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4
Q

What are the causes of sickle cell anaemia?

A
  • single base substitution
  • CTC → CAC
    • mRNA: GAG → GUG
    • glutamine 6 (in beta chain) → valine
      • amino acids
  • Hb^A - in healthy humans
    • Hb^S
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5
Q

What are the results of haemoglobin mutation (sickle cell anaemia)?

A
  • deoxygenated haemoglobin stick to each other
    • stiff fibres in red blood cells
    • deformation of RBC
    • fragile - from 30 to ~4 days
  • inability to replace them causes anaemia
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6
Q

What is a mutation?

A
  • random change
    • no mechanism behind it
  • most common: base substitution
    • one base is exchange for another
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7
Q

What are the steps of mutation and potential causes?

A
  1. change of base in gene sequence
  2. change of codon in RNA sequence
  3. (potential) change in amino acid sequence
  4. (potential) change in protein structure
  5. (potential) change of loss of protein function
  6. change of organism’s physiology
  • mutations are random = never beneficial
    • neutral or harmful
    • can be passed (in gametes)
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8
Q

What is a genome?

A
  • whole DNA of an organism
    • coding and non-coding parts
    • 46 linear chromosomes + DNA in mitochondrion (in humans)
    • in plants: chromosomes + DNA in mitochondrion and chloroplasts
    • in prokaryotes: circular DNA
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9
Q

What is the link between malaria and sickle cell anaemia?

A

> malaria

- different red blood cells shapes prevents from reproduction of Endemic falciparum (malaria protist)

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10
Q

What was the Human Genome Project?

A
  • base sequence of a whole human genome
  • mine of data
    • which sequences code for proteins
    • non-coding parts of DNA are important
    • comparison between humans and other species
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11
Q

How do chromosomes differ in eukaryotic and prokaryotic cell?

A
  • eukaryotes
    • linear (in nucleus)
      • forms nucleosomes
    • non-coding sequences
  • prokaryotes
    • circular
    • nucleoid = DNA + cell membrane
    • compact (no repetitions)
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12
Q

What is a chromosome?

A
  • entire chain of DNA along with a group of stabilising proteins
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13
Q

What was the procedure of Cairn’s technique and what did the results show?

A
  • autoradiography
  1. DNA labelled with radioactive thymidine
  2. during DNA replication
    • isotope incorporated into new DNA strand
  3. the cell was placed in dialysis membrane and lysozyme was used to break down its walls
    • DNA in membrane
  4. radioactivity allows exposure of photosensitive film (radioactively-sensitive emulsion)
    • tritium decayed
      • image on film
      • autoradiograph
      • conformation of ‘replication fork theory’ → bidirectional
      • estimation of chromosomal / DNA length
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14
Q

What are plasmids and what is their role?

A
  • in prokaryotes
  • small circular DNA bits (naked)
  • exchanged between bacteria
    • antibiotic resistance
  • plasmids do not replicate in the same time as DNA
    • not passed during division
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15
Q

What is the role of nucleosome?

A
  • protecting DNA from harm
  • changing structure
    • information in DNA used or not
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16
Q

What is the structure of nucleosome?

A
  • 8 histone proteins (+ charge)
    • histone tails reach out to neighbouring nucleosomes
      • tightly packing
  • 2 loops of DNA (- charge phosphate group)
  • differences in charges cause DNA to wrap around histones
  • in nucleus
    • enzymes modify tails
    • weakening interactions between nucleosomes
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17
Q

What are homologous chromosomes?

A
  • pair
    • one from each parent
    • corresponding sequences
    • during meiosis they pair
  • 46 chromosomes
    • 2 sets of 23 chromosomes
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18
Q

How many chromosomes are in human cell?

A
  • haploid - 1 chromosome of each kind: 23
    • sex cells (to reproduce)
  • diploid - 2 homologous chromosomes of each kind: 46
  • polyploid
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19
Q

What is a karyogram?

A
  • homologous pairs of chromosomes of decreasing length
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20
Q

What are sex chromosomes?

A 
> XX - female 
> XY - male 
	- Y is smaller 
> human body functions without duplicate of X (in XY)
	- for XX
		- X-inactivation (random in each cell)
		- differences between twins
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21
Q

Why does genome size vary and what does it depend on?

A

> size and number of chromosomes
complexity (not proportional)
some organisms may have many non-coding areas

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22
Q

What are promoters?

A

> binding site of RNA polymerase

- determine whether transcription occurs

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23
Q

What are expression regulating sequences?

A
  • enhancer
  • silencer
  • promoter-proximal sequence
  • terminator - ending part
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24
Q

What is an operon?

A
  • group of proteins having similar functions
  • sequenced together
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25
Q

How is gene expression of absorption of lactose regulated in E. coli?

A
  • gene expression is dependent on environment
  • operon: lacZ, lacY, lacA
    • break down lactose (glucose for energy)
  • repressor - protein inhibiting expression of breaking down lactose (if there’s no lactose in cell)
    • RNA polymerase cannot bind to operator (promoter)
    • when lactose is present, it binds to repressor
      • expression of gene starts
  • presence of glucose
    • bacteria uses glucose (easier)
    • CAP site
      • CAP protein binds (low glucose)
        • increased expression
        • cAMP helps with binding
        • high level of transcription
    • high glucose levels
      • no cAMP produced
26
Q

What happens during cell division?

A

> cell may divide into 2 daughter cells

- different functions = different expression rates

27
Q

What is the direction of transcription?

A
  • RNA strand: 5’ → 3’
    • sense strand is the same
  • antisense strand: 3’ → 5’
28
Q

How does environment impact gene expression?

A
  • amount of sunlight
  • temperature
    • Siamese cats
      • mutant allows for production of pigment only in low temp.
29
Q

What happens in the first step of transcription (initiation)?

A
  • promoter (usually TATA)
  • transcription factors bind to DNA - initiation complex
    • find promoters
    • help binding of RNA polymerase
    • ATP is added to start the process
      • ADP and P
    • released when transcription begins
    • activators and repressors (increase and decrease the rate)
    • silencers and enhancers
      • eukaryote: set of proteins
30
Q

What happens in elongation (transcription)?

A
  • as RNA polymerase goes it unwinds the helix
  • RNA polymerase transcribes the DNA sequence
    • producing RNA strand by attaching complementary base pairs
31
Q

What happens in termination (transcription)?

A
  • transcription stops as the terminator sequence is reached
    • RNA dissociates from RNA polymerase
  • pre-mRNA is formed
32
Q

What are the post-transcription modifications (capping and poly-adenylation)?

A
  • only in eukaryotes
  • preparing RNA for translation
    • quality control
    • protection from damage
  • capping
    • addition of 5’ cap
    • protects the end
  • poly-adenylation
    • adding A bases (3’)
33
Q

What happens during mRNA splicing and what is its role?

A
  • introns (non-coding) are cut out
    • later used
  • jointing exons
  • alternative splicing
    • some exons can be cut out
    • make products more complex (different variations)
  • made by spliceosomes
34
Q

What is epigenetics?

A
  • chemical modifications of DNA or proteins affecting DNA
    • during development
    • reset when forming gametes
35
Q

How is transcription regulated (changes in DNA and chromosomes)?

A
  • DNA methylation
    • direct modification
    • adding ethyl group to cytosine
      • interactions of proteins with DNA
      • gene silencing
  • modification of histones
    • histone tails have positive charge
    • acetylation = adding acetyl group
      • neutralisation of histones
      • DNA is negative
        • less coiling
      • more transcription
    • methylation = adding methyl group
      • DNA more coiled (condensation)
      • less transcription
36
Q

What happens to epigenetic tags in gametes?

A
  • dividing cells still have tags
    • when joined together cells tags are erased
    • cells are reprogrammed
      • parts of the tags can stay
37
Q

What happens during translation?

A

> polypeptides are synthesised

> amino acid sequence determined by base sequence of mRNA

38
Q

Where does translation take place?

A
  • in cytoplasm (rough endoplasmic reticulum)
  • ribosomes
39
Q

What is the structure of ribosome?

A
  • 2 subunits: large and small
  • rRNA
  • binding site for tRNA
    • 2 tRNAs can bind at the same time
    • A (aminoacyl) site
      • recognition and interaction of codon and anticodon
    • P (peptidyl) site
      • holds peptide-caring tRNA
    • E (exit) site
      • release discharged tRNA
  • binding site for mRNA
  • unit ‘S’ (svedbergs)
    • measure of speed of molecule in centrifuge
    • do not add up
      • once bound subunits lose their mass
    • prokarya: 70S (50S big, 30S small)
    • eukarya: 80S (60S big, 40S small)
40
Q

What are codons?

A
  • sequence of three bases of mRNA that are translated into 1 amino acid
    • START codon - Methionine
    • STOP codon inhibit translation
    • 64 possible codons (4^3)
  • 24 amino acids
    • some codons code for the same aa
      • genetic code is degenerate
41
Q

Why is genetic code universal?

A
  • each codon translates into the same amino acids among different organisms
  • there are some exceptions: mitochondria, yeast, protists
42
Q

What is the role of mRNA in translation?

A
  • produced in transcription
  • information about sequence
  • structure
    • reading part (from START to STOP)
    • 5’ → 3’
43
Q

What is the structure of tRNA?

A

> anticodon
- complementary sequence that reads codons
site for attaching amino acid
- sequence CCA (3’ end)

44
Q

How is tRNA activated?

A
  • tRNA-activating enzyme (aminoacyl-tRNA-synthetase)
    • active site of enzyme is anticodon and amino acid specific
    • ATP = AMP + PPi
      • ester bonds between tRNA and amino acids
  • process
    1. amino acid and ATP binds
    2. amino acid activation by AMP
      • pyrophosphate is released
    3. tRNA binds to enzyme
      • amino acid bind to tRNA (covalent bond)
      • AMP released
    4. charged tRNA released
45
Q

What happens in initiation of translation?

A
  • positions small subunit (near START of mRNA)
  • tRNA with Met binds
    • in P site
  • big ribosomal unit attracted
  • elongation starts
46
Q

What happens in elongation of translation?

A
  • peptidyl-tRNA binds to P site
  • charged aminoacyl-tRNA enters A site
    • anticodon binds to codon
  • peptide transferase transfers polypeptide to A-bound tRNA
  • translocation
    • ribosome moves 3 nucleotides ahead towards 3’ end
      • discharged tRNA → E site
        - peptide-carrying tRNA → P site
        - A site emptied
47
Q

What happens in termination of translation?

A
  • STOP codon is reached
    • tRNA is released
    • polypeptide dissociates
  • ribosomal units separate
48
Q

How does translation occur in prokaryotes?

A

> transcription and translation occur simultaneously
- no nucleus
- no introns
- less ability to control the process
polysome
- multiple ribosomes translating the same mRNA

49
Q

What is the difference between bound and free ribosomes?

A 
> free ribosomes 
	- produce proteins for usage in cell 
> bound ribosome 
	- on rough endoplasmic reticulum 
	- proteins for secretion
50
Q

What are different protein structures?

A
  • primary structure
    • covalent peptide bonds
    • sequences of polypeptides
  • secondary structure
    • H-bonds between carboxyl group (C=O) and amino group (N—H)
    • beta-pleated sheets
    • alpha-helix
  • tertiary structure
    • 3D structure
    • R group with water medium
      • R group + with R group -
      • hydrophobic amino acids stick to each other
      • polar R-groups form H-bonds
      • disulphide bridges
  • quartenary structure
    • more than 1 polypeptide
    • non-polypeptide elements
51
Q

How does gel electrophoresis work?

A
  • separate proteins according to size
  • process
    • DNA samples are put in a gel
      • charged negatively so it will move towards + side
    • small fragments move faster
52
Q

What is the role of DNA profiling?

A
  • paternity tests
    • DNA of mother, child and potential father
  • forensic investigations
    • blood stains, hair, semen
    • DNA of victim and suspects are compared with the sample
53
Q

What are stages of DNA profiling?

A

> sample DNA obtained
sequences of DNA that vary are copied by PCR
- split into fragments (restriction endonucleases)
gel electrophoresis
pattern of bands obtained
- compared with suspect and victim

54
Q

How does genetic modification work?

A
  • genetic code is universal
  • genes transferred between species
    • new characteristics
  • genetically modified organism (GMO)
    - DNA from other species (US definition)
    - crossing is not GMO
    - transgenic organisms
55
Q

How are genes transferred to bacteria?

A

> mRNA secreted from human cells
- reverse transcriptase
- complimentary DNA (cDNA)
from bacterium cell plasmid is obtained
- part of it cut with restriction enzyme
- sticky ends = cutting 2 strands at different points
cDNA and plasmid fuse
- DNA ligase
new plasmid introduced to bacterium
bacterium replicates
- gene expression of new fragment (ex.: insulin)
bacteria is separated and substance purified
available for usage

56
Q

Assessment of one benefit and risk of GM crops

A
  • example: Golden Rice
  • rice that produces beta carotene
    • supply of vitamin A needed in countries where a lot of rice is consumed (Asia)
  • benefit (health): the nutritional value of crops is improved
  • risk (environmental): cross-breeding (or spreading) to wild plants, uncontrollable effects
    • contaminating wild rice
57
Q

Assessment of risks and benefits of GM of Bt corn

A

> plants produce toxins that kill insects
benefit (environmental): less pesticides are used
risk (environmental): non-target organisms could be affected by toxins
- monarch butterfly
- feed on milkweed near corn

58
Q

What are clones?

A
  • genetically identical organisms
    • single parental cell
  • asexual reproduction
  • twins (monozygotic)
    • zygote divides into 2 cells
    • 2 embryos
59
Q

What are examples of natural cloning?

A
  • garlic bulb
    • by photosynthesis enough energy to produce group of bulbs
  • strawberry
    • plantlets at the end of plant
      • grow roots
      • independent from parent plant
60
Q

How can animals be cloned?

A

> embryos are pluripotent
- can develop in every tissue
embryo broken artificially can produce clones
characteristics cannot be chosen

61
Q

How can adult animals be cloned?

A
  • cells are differentiated
  • in frog
    • once a nucleus is put in a new cell it develops as if a zygote
  • in humans — stem cells
62
Q

Producing Dolly

A
  • somatic-cell nuclear transfer
  • cells taken from udder of adult sheep
    • cultured in lab
  • unfertilised egg from another sheep
    • nucleus removed
  • egg cell formed
    • pulse of electricity
  • embryo transferred to uterus of another sheep
  • surrogate mother gave birth to Dolly

Biology HL (14 decks)

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