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Semester 1- MTM > Storage and Replication of Genetic Information > Flashcards

Storage and Replication of Genetic Information Flashcards

1
Q

what is the “central dogma of molecular biology”?

A

the theory that genetic information flows only in one direction, from DNA, to RNA, to protein, or RNA directly to protein.

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2
Q

what is the 2 step process in making proteins?

A

transcription
translation

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3
Q

what is the enzyme that turns RNA back into DNA?

A

Reverse transcriptase (retrovirus)

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4
Q

what are the similarities in the the structure of DNA and RNA?

A

Both have a sugar phosphate backbone
both have bases

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5
Q

what is the structure of DNA?

A

double stranded
helical structure
Hugh molecular weight
very long strand

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6
Q

what is the structure of RNA?

A

single stranded
heterogenous (vary) in size - bc the genes that they come from vary in size
h- bonding between base pairs in the strand - INTRA- molecular base pairing (as opposed to INTER molecular in DNA)

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7
Q

what are the differences in structure of DNA and RNA?

A

DNA- DEOXYribose sugar
RNA- ribose sugar
DNA nucleotides (ATCG bases)
RNA nucleotides (AUCG bases)

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8
Q

what is the structure of a nucleotide?

A

5 carbon sugar
attached to a phosphate
nitrogenous base

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9
Q

why is RNA and DNA’s ribose sugar different (in terms of structure)?

A

Ribose has -OH group at carbon 2, whereas Deoxyribose has only H

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10
Q

what bonds are between nucleotides?

A

phosphodiester linkages

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11
Q

how are thymine and uracil both able to pair up with adenine?

A

they are both structurally very similar with the only difference being that thymine has an extra methyl group - h- bonding is able to happen

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12
Q

what is the difference in stability of RNA and DNA?

A

DNA is used as long-term store of genetic info as it is very stable
RNA is unstable due to presence presence of -OH on ribose C2- it reacts with the phosphate in the backbone causing cleavage of sugar-phosphate backbone (-OH acts as a Lewis base - electron pair donor)

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13
Q

what are the pyramidines and purines?

A

A & G = purine
T & C = pyrimidine

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14
Q

why do purines and pyramidines pair together?

A

There is only room for one purine (double ring) & one pyrimidine (single ring) base

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15
Q

how many hydrogen bonds are between each base?

A

Adenine and Thymine and complementary bases joined by 2 hydrogen bonds
Cytosine and Guanine are joined by 3 hydrogen bonds (slightly stringer pairing)

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16
Q

what is the structure of a DNA strand?

A

has a 5’ end and a 3’ end (sequence read from the 5’ end to the 3’ end)
is antiparallel
the base sequence of one strand determines the base sequence of the other strand

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17
Q

what is a chromosome?

A

A single molecule of DNA

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18
Q

what is a gene?

A

a specific stretch of DNA where the sequence contains genetic instructions

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19
Q

what is the organisation of the human genome?

A

contains more protein coding than non- protein coding genes
protein coding genes vary in size and internal organisationorganisiation (no. of introns and exons)
genes unevenly distributed between and within chromosomes
genes can be on one strands of DNA; some genes within introns of other genes

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20
Q

other than the nucleus, where can DNA be found?

A

mitochondria has 37 genes
16,600 DNA bases
that also needs to be replicated

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21
Q

what does the human chromosome consist of?

A

23 pairs
22 are autosomes (non-sex chromosomes)
1 pair determines sex- either XY or XX

DNA packaged into chromatin by histones and other chromosomal proteins

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22
Q

what kind of staining allows us to see chromosomes?

A

Old fashioned technique…
Giemsa staining- mitotic chromosomes (highly condensed) were stained which revealed their structural differences

A more modern technique…
chromosome “painting”- specific probes of different colours reveal each chromosome pair

23
Q

what different elements is the human genome comprised of?

A

Only around 5% of the human genome is genes. The rest are gene regulatory elements:

Promoter & enhancer elements
Introns & exons
Repeat elements

24
Q

what are promoter and enhancer elements?

A

regulate when genes are tuned on or off
Usually multiple per gene
promoter elements usually found upstream (5’)
enhancer elements can be found anywhere i.e upstream (5’) and downstream (3’) of the gene
can also be very far away from the gene

25
Q

what are introns and exons?

A

Introns (intervening) = non-coding DNA - make up most of the DNA
Exons (expressed) = coding DNA
introns removed from pre mRNA by splicing mechanisms

26
Q

what are repeating elements?

A
  • Represent 25% of our DNA
  • Chunks of a repeated sequence that do not encode for a protein.
  • Derived from RNA viruses - reverse transcription of viral RNA into human DNA
  • sequences shut down in the body but still remain in the genome
  • Can be used in DNA fingerprinting
  • is called ‘satellite DNA’
27
Q

what is satellite DNA and where are they found?

A

they are reacting sequences of DNA
mainly present in heterochromatin or the tightly packed regions of chromosomes in centromeres

28
Q

what are the 2 types of satellite DNA?

A

Mini- satellite:
1000 copies of 10BP repeat units
highly polymorphic (no. or repeats vary between individuals)
can be found at telomeres

Micro- satellites:
3BP repeat units e.g CAG
Usually found in introns (non-coding) DNA

29
Q

what is the purpose of mini- satellites?

A

its unknown
HOWEVER, can cause problems
e.g mispairing during cell division to give:
- large scale duplication/ deletion between homologous chromosomes
- translocation of DNA between non- homologous chromosomes

30
Q

what is the role of these multiply repeated sequences? (telomeres)

A

telomeres:
protect the end of the chromosome and allows replication all the way to the tip
this is bc long tracts of repeats can be unstable leading to deletions below the telomeres

31
Q

what is the role of these multiply repeated sequences? (centromeres)

A

centromeres:
(point were mitotic spindle fibres attach)
- essential for segregation during cell division
- specific sequences in repeating unit are recognised by proteins that bind to the centromeric sequences

32
Q

what practical applications do repeating units have?

A

Everyone has unique introns/ repeating units
allows for use in forensics and paternity testing

33
Q

what is the role of RNA other than it being translated into proteins?

A

rRNA and tRNA involved in translation of mRNA
some RNA molecules modify other RNA molecules (e.g splicing involving snRNA; snoRNA)
microRNA affect the stability of mRNA

34
Q

how is DNA packaged?

A

1) DNA double helix wraps around a nucleosome (formed from 8 histone molecules)
2) Nucleosomes then fold up to produce a 30nm fibre (chromatin)
3) Fibres compressed further to produce a larger fibre (250-300nm)
4) Fibres coil up to produce chromatid of a chromosome

35
Q

what is chromatin?

A

DNA-protein complex present during interphase (any phase where cell is not replicating)

36
Q

why can’t protein synthesis happen during mitosis?

A

because the DNA is so condensed so enzymes e.g. RNA polymerase can’t access it.

37
Q

what happens in the nucleolus?

A

its a large structure within the nucleus where ribosomal RNA is transcribed and ribosomal subunits are assembled

38
Q

what are the 2 forms that chromatin can exist in?

A

euchromatin
heterochromatin

39
Q

what is euchromatin and where is it found?

A

Euchromatin (in interphase)
- prevalent in gene rich areas
- open conformation of DNA in nucleus
- allows for transcription as its a less compact and unfolded structure
- so allows regulatory proteins & RNA polymerase complexes to bind more easily to DNA

40
Q

what is heterochromatin and where is it found?

A
  • highly condensed region of an interphase chromosome
  • generally gene poor and transcriptionally active
  • found at the centromere and telomeres usually but be anywhere on the DNA strand
41
Q

what are the 2 types of heterochromatin and give examples?

A

Facultative heterochromatin – in a TEMPORARILY inactivated (condensed) state.
Example: X chromosome inactivation in female mammals: one X chromosome is packaged as facultative heterochromatin and silenced, while the other X chromosome is packaged as euchromatin and expressed.
Constitutive heterochromatin – always inactive & condensed, present at fixed location
Example: centromeres and telomeres

42
Q

define transcriptome

A

the set of all RNA molecules from protein coding (mRNA) to noncoding RNA, including rRNA, tRNA, lncRNA, pri-miRNA etc
dynamic
varies from cell to cell

43
Q

define proteome

A

the complete set of proteins expressed by an organism
dynamic
varies from cell to cell

44
Q

what is needed for transcription to be carried out?

A

Carried out by RNA polymerase II
Building blocks: Nucleoside Triphosphates (CTP, UTP, GTP, ATP)
Enzyme requires DNA template
RNA is synthesised in a 5’ to 3’ direction

45
Q

how is the template strand used for transcription of RNA?

A

Only one of the two strands of DNA contains the code for the protein to be synthesised. This is the sense strand and runs 5’ to 3’.
The other strand (3’ to 5’) is a complimentary copy of the sense strand (antisense strand) and does not code for a protein. It acts as a template strand during transcription so the RNA strand has the same base sequence as the sense strand. I.e. if the sense strand has codon GTC the mRNA strand will have codon GUC which then represents the amino acid.

46
Q

what is a transcription bubble and why is it formed?

A

Local melting of DNA produces 20-30 bp transcription bubble - it moves along anti-sense strand with RNA Polymerase producing the RNA stand.

47
Q

how is splicing carried out?

A

As the RNA stand is being produced it is being processed. This occurs at spliceosomes (composed of protein + snRNA [small nuclear]) which remove introns from pre-mRNA to form mature mRNA
This happens co-transcriptionally – same time as RNA is being produced.

48
Q

what is translation?

A

the process through which information encoded in mRNA directs the addition of amino acids to form polypeptide

49
Q

what is tRNA?

A
  • 3 ‘hairpin’ stem-loop structure
  • tRNA has a clover leaf shape – stabilised by hydrogen bond between bases.
  • tRNA is an adaptor molecule which links a specific amino acid to a codon.
  • The anti-codon hydrogen bonds with complementary codon on mRNA (CUU)
50
Q

what is rRNA?

A
  • Ribosomes are made of two subunits, one large and one small.
  • These subunits are composed of almost equal amounts of protein and ribosomal - rRNA.
  • Ribosome have a binding site for mRNA on the small subunit
    This has two cavities:
    P- site
    A-site
51
Q

describe the process of translation

A
  1. mRNA joins to the binding site on the ribosome (at small subunit).
  2. Initially the codon in the P site is recognised by a tRNA molecule with a complementary anticodon with an amino acid attached (methionine). It binds to the mRNA at the P site with H bond between bases.
  3. A second tRNA with a complementary anti codon to the codon at the A site binds (with H bond to mRNA) with the corresponding amino acid.
  4. Peptide bond form between adjacent amino acids catalysed by the enzyme peptidyl transferase
  5. The ribosome then slides along from 5’ end to 3’ end and the tRNA molecule in the A site goes to p site and the other tRNA released.
  6. Another complementary tRNA binds to the A site and the process is repeated generating an amino acid chain until a stop codon is reached.
  7. More than one ribosome attaches to the mRNA strand and they move along behind one another - efficient as multiple protein copies generated simultaneously
52
Q

define polyribosome

A

a cluster of translating ribosomes held together by a strand of messenger RNA

53
Q

how does the genetic code work?

A

3 bp is a codon
read in 5’ to 3’ direction
each AA is coded for by 1 codon
There are many codons for the same AA - degenerative code (20 amino acids but 64 codons)
universal - same code in every organism
non- overlapping - every 3 read separately
3 possible reading frames
stop codon: UAA, UAG, UGA
start codon: AUG (methionine)

54
Q

how does a mutation effect a protein sequence?

A

Consequences depend on nature and position of mutation
- biggest impact if in the coding or regulatory region of a gene
Deletion or insertion of one or more nucleotides - may not result in -ve result as same no. of bases could be deleted/ inserted (no frameshift mutation)
Substitution or point mutation- alteration of a single base position

Semester 1- MTM (15 decks)

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