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Kaplan USMLE Review > The Genetic Code, Mutations and Translation > Flashcards

The Genetic Code, Mutations and Translation Flashcards

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USMLE® Step 1 flashcards
1
Q

β-thalassemia results from what type of mutations?

A

A mutation in the splice site most of the time. There could also be nonsense mutations and missense mutations.

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2
Q

What is the start codon for prokaryotes? What is the corresponding amino acid it codes for?

A

AUG, formylmethione

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2
Q

What are general examples of proteins that complete their translation on free cytoplasmic ribosomes?(2 points)

A

cytoplasmic proteins and mitochondrial proteins (encodes by nuclear genes)

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3
Q

What are two important signals used to ensure protein delivery to the appropriate organelles?(2 points)

A

The N-terminal hydrophobic signal sequence used to ensure translation on the RER and the phosphorylation of mannose residues important for directing an enzyme to a lysosome

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4
Q

What is the polarity of protein synthesis during translation?

A

Proteins are translated from the amino group to the carboxyl group

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4
Q

What are the two general roles of proteasomes?

A

they produce antigenic peptides for presentation by class I MHC molecules and they degrade polyubiquinated proteins to peptides

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5
Q

What amino acid(s) have only one codon?

A

Methionine and Tryptophan

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6
Q

What is the biochemical defect leading to osteogenesis imperfecta? What are the major symptoms?(1-3 points)

A

mutations of the collagen genes. Skeletal deformities, blue sclera, fractures

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7
Q

What is the biochemical defect causing Menkes disease? What are the major symptoms?(3-6)

A

A lack of proper cross-linkage by lysyl hydroxylase due to a copper deficiency. The major symptoms are depigmented (steely) hair, arterial tortuosity, rupture, cerebral degeneration, osteoporosis and anemia

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8
Q

For those amino acids having more than one codon, what special sequence or property do you see with their bases?

A

The first two position on the codon is the same but the last position often varies

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8
Q

What is another name for the A site and the P site

A

aminoacyl site and peptidyl site

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8
Q

What is the level of protein shape: folding of the amino acid into an energetically stable structure

A

secondary

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9
Q

Where does translation take place in prokaryotes? Where does translation take place in eukaryotes?

A

cytoplasm in both cases

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10
Q

As proteins passes through ER and Golgi, they acquire what type of links?(1-4 points)

A

oligosaccharide side links to serine or threonine residues(O-linked) or asparagine residues(N-linked)

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11
Q

Peptidyl transferase is apart of what ribosomal subunit?

A

large subunit

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12
Q

When does cross-linking occur during collagen synthesis?

A

This occurs in the extracellular matrix where the tropocollagen forms fibrils through cross-links via the enzymatic activity of lysyl oxidase which requires oxygen and copper to function

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13
Q

expansion in coding regions cause protein product to be longer than normal and unstable Disease often shows anticipation in pedigree. What type of mutation?

A

expansion mutation

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13
Q

When do large segment deletions usually occur?

A

During an unequal crossover of homologous chromosomes during meiosis

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13
Q

Mutations in the splice site may result in spliceosomes performing what type of errors?(1-3)

A

delete nucleotides from the adjacent exon; leave nucleotides of the intron in the process mRNA; use the next normal upstream or downstream splice site, deleting an exon from the processed mRNA

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13
Q

What is Gray Baby syndrome? What is he biochemical reason for the disease? What are the symptoms?(1-3 points)

A

A disease that results from the administration of chloramphenical to newborns. The newborn doesn’t have a sufficient amount of UDP glucuronyl transferase to eliminate the drug from its system. The symptoms are cyanosis, low blood pressure and death

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14
Q

What type of mutation: NEW CODON SPECIFIC SAME AMINO ACID? Hw does it effect protein?

A

Silent mutation; no effect

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15
Q

What is the specific action of the aminoacyl tRNA synthetase?

A

It catalyze the transfer of the two high energy phosphate bonds from ATP and binds the corresponding amino acid to the 3’ end of the tRNA molecule

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16
Q

The tertiary structure f amino acids are reinforced by what type of bonds?(2 points)

A

weak bonds and strong bonds like disulfide bonds

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17
Q

The majority of cases of cystic fibrosis result from what?(1-3 points)

A

deletion of phenylalanine at position 508 which interferes with proper protein folding and the post translational processing of oligosaccharide side chains

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17
Q

What type of collagen: amorphous?

A

type IV

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18
Q

What is the completed initiation complex during protein synthesis?(3)

A

The large ribosomal subunit, the small ribosome subunit and the initiator aminoactyl-tRNA complex

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19
Q

What are the general biochemical steps that occur when a stop codon is reached during protein synthesis?

A

Peptidyl transfers with the assistance of other releasing factors hydrolyzes the completed protein from the final tRN in the P site.

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19
Q

What type of collagen: basement membranes?

A

type IV

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19
Q

What type of collagen: bundles of fibers high tensile strength?

A

type I

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20
Q

Does all translation of mRNA being in free ribosomes or does the translation of particular mRNA begin on the rough endoplasmic reticulum?

A

They all begin in free ribosomes within the cytoplasm

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21
Q

What are major symptoms of I-Cell Disease?(5-15)

A

coarse facial features, gingival hyperplasia, macroglossia, cranio abnormalities, joint immobility, clubfoot, claw-hand, scoliosis, psychomotor retardation, growth retardation, cardiorespiratory failure, death in first decade, bone fracture and deformities, mitral valve defect, secretion of active lysosomal enzymes into blood and extracellular fluid

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23
Q

What type of mutation: new codon is stop codon? What is the effect on protein?

A

nonsense; shorter than normal; usually non-functional

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25
Q

What type of mutation: 5’ splice site(donor) or 3’ splice site(acceptor)? What is the effect on protein?

A

variable effects ranging from addition or deletation of a few amino acids to deletion of an entire exon

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26
Q

What type of sequence is placed on preproinsulin?

A

N-terminal hydrophobic sequence

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27
Q

It is a point mutation that replaces any purine-pyrimidine base pair with a purine-pyrimidine base pair

A

transition mutation

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27
Q

A defect of what step in collagen synthesis results in scurvy?

A

The hydroxylation of prolyl and lysyl residues are completed by lysyl and prolyl hydroxylases which require vitamin C to function.

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28
Q

Ehlers-Danlos Type IV and Keloid formation are disease associated with what type of collagen?

A

type III

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29
Q

Each codon consist of how many bases?

A

Three bases

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30
Q

What are the three stages for protein synthesis?

A

initiation, elongation and termination

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31
Q

The (f)met-RNA initially binds to what site? The met-tRNA binds to what site?

A

the both bind to the P site of the completed initiation complex

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32
Q

What is a transgression mutation?

A

It is a point mutation that replaces a purine-pyrimidine base pair with a pyrimidine-purine base pair

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33
Q

What factors are needed for all of the stages of protein syntesis?(4 points)

A

initiation factor, elongation factor, release factor and GTP

34
Q

Elongation takes place in how many steps?

A

three steps

35
Q

What is the biochemical cause and consequence of α1-anti-trypsin deficiency?

A

It results in the production of variants of the antitrypsin protein as a consequence of point mutations. These mutated proteins sometimes accumulate in the endoplasmic reticulum of hepatocytes and cause liver failure.

35
Q

What is the amino acid unique to collagen? How is it produced? Where does it occur?

A

Hydroxyproline is an amino acid unique to collagen. It is produced via the hydroxylation of prolyl residues at the Y position in the pro collagen chains as it passes through the rough endoplasmic reticulum.

36
Q

What enzyme is required for amino acid activation? What is the required energy contribution? What is the name of the product?

A

aminoacyl-tRNA synthetase. The reaction required two high energy bonds from ATP. The final product is aminoacyl-tRNA.

37
Q

What is I-Cell disease?(3 points)

A

Some genetic defect resulting in the impaired function of n-acetylglucosamine-1 phosphotransferase. Lysosomal enzymes aren’t directed to the lysosome. They’re secreted not the extracellular space.

37
Q

What is the genetic inheritance of Ehlers Danlos Type IV? What type of genetic defect results in this disease? What are characteristic features of this disease?(4-8)

A

Autosomal dominant. A mutation in the pro collagen type III gene. Characteristic symptoms are going to be thin, translucent skin, arterial, uterine and intestinal rupture; easy bruising

38
Q

Menkes disease could also result from the genetic mutation of what gene?

A

ATP7A

39
Q

Do codons code for only one amino acid or does one codon code for multiple amino acids?

A

Each codon specifies no more than one amino acid

41
Q

What is the genetic inheritance for Huntington’s disease? What is the mean age of onset? How do the symptoms appear?

A

Huntington disease is autosomal dominant. The mean age of onset is 43-48 years-old. The symptoms appear gradually until the person dies.

42
Q

What are general examples of proteins that complete their translation on the rough endoplasmic reticulum?(2-3)

A

secreted proteins, lysosomes and proteins that are to be entered in the cell membrane

44
Q

The Shiga toxin inhibits what?

A

The 28S rRNA in the 60S large ribosomal subunit found in eukaryotes

45
Q

What are the symptoms for Huntington’s disease?(4-8)

A

the firstlings are odd disturbance, impaired memory, hyperreflexia, abnormal gait, chorea, dystonia, dementia and dysphagia

46
Q

What are the elongation factors that are needed for aminoactyo-tRNa binds to A site in both prokaryotes and eukaryotes?( 3 points)

A

EF-TU and EFTS in prokaryotes. eEF-1 for eukaryotes.

46
Q

What enzyme forms the bond between the amino acid(s) in the P site and the amino acid in the A site?

A

peptidyl transferase

48
Q

When and where does translation take place in eukaryotes? When and where does translation take place in prokaryotes?

A

Translation takes place after transcription, which takes place in a separate location in the nucleus. Translation takes place after pre-mRNA processing in the cytoplasm in eukaryotes. Translation and transcription takes place at the same time and at the same location, cytoplasm, in prokaryotes.

50
Q

What type of mutation: large segment deletion(unequal crossover in meiosis)? What is the effect on protein?

A

unequal cross over in meosis; loss of function; shorter than normal or entirely missing

52
Q

Where does the energy come from to form the peptide bond during translation?

A

The high energy rich bond between the 3’ region of the tRNA and the amino acid supplies the energy to form the peptide bond

53
Q

What is the level of protein shape: positioning of the secondary structures in relation to each other to generate high-order three dimensional shapes

A

tertiary

54
Q

What type of signal is added to a protein while it is in the endoplasmic reticulum to ensure transfer to Golgi?

A

the protein is glycosylated

55
Q

What is the size of the nascent peptide on the ribosome closest to the 3’ end of the mRNA molecule?

A

It has the longest nascent peptide

56
Q

Goodpasture syndrome, alport disease and epidermolysis bulls are disease associated with what type of collagen?

A

type IV

58
Q

What type of mutation: addition or deletion of base(s)? What is the effect on protein?

A

frameshit/in frame; usually nonfunctional; often shorter than normal

59
Q

What is the unique repeating tripeptide that makes up collagen?

A

Gly-X-Y-Gly-X-Y-Gly-…

61
Q

What is the breakdown for the general purpose for the codons?

A

61 codons code for amino acids and 3 codons are stop codons

62
Q

What are the required elongation factors needed for the translocation of ribosome 3 nucleotides along the mRNA for eukaryotes and prokaryotes?( 2points)

A

EF-G in prokaryotes and eEF-2 in eukaryotes

63
Q

What antibiotic inhibits mitochondrial protein synthesis?

A

chloramphenicol

64
Q

What is the level of protein shape: in proteins with multiple subunits, describes the interaction between the subunits?

A

quaternary

66
Q

How does aminoacyl tRNA synthetases protect itself from making errors?

A

It has a self-checking mechanism to prevent errors but if a wrong amino acid is attached to a tRNA, there is a no mechanism that would prevent the synthesis of an incorrect protein

67
Q

Initiation begins with what subunit of the ribosomes binding to what structure of the eukaryotic or the prokaryotic mRNA?

A

The small subunit binds to the 7-methylguanosine cap on the 5’ region of the eukaryotic mRNA. The small subunit binds to the shine-dalgarno sequence in the untranslated region of the mRNA in prokaryotes

68
Q

What are the important steps of collagen synthesis?(8 steps)

A

Prepro-α chains containing a hydrophobic signal sequence are synthesized by ribosomes attached to the RER. The hydrophobic signal is removed by signal peptidase in the RER to form pro-α chains. Selected pralines and lysins are hydroxylated by proudly and lysol hydrolyses. These enzymes, located in the RER, require abscrobate (vitamin C), deficiency of which produces scurvy. Selected hydroxylysines are glycosylated. Three pro-alpha chains assemble to form a triple helical structure (pro collagen) which can now be transferred to the golgi. Modification of oligosaccharide continues in the Golgi. Pro collagen is secreted from the cell. The pro peptidases are cleaved fro the ends of pro collagen by proteases to form collagen molecules (also called tropocollagen). Collagen molecules assemble intro fibrils. Cross-linking involvves lysyl oxidase, an enzyme that requires O2 and copper. Fibrils aggregate and ross-link to form collagen fibers

69
Q

How many codons exist?

A

64 codons

70
Q

What is the level of protein shape: sequence of amino acids specific in the gene

A

primary

71
Q

Is it possible for a amino acid to have multiple codons?

A

Yes

72
Q

What type of collagen: blood vessels, granulation tissue?

A

type III

74
Q

What is the start codon for eukaryotes? What is the corresponding amino acid it codes for?

A

AUG, methionine

75
Q

What type of collagen: bone, skin, tendons?

A

type I

76
Q

What is a mutation?

A

It is any permanent, heritable change in the DNA base sequence of an organism

77
Q

What are the molecules that assist in folding of protein?

A

Chaperones

78
Q

The secondary structure of amino acids are reinforced by what type of bonds?

A

hydrogen bonds

79
Q

What type of collagen: thin fibrils; structural?

A

type II

80
Q

What are the stop codons?(3 points)

A

UAA, UAG, UGA

81
Q

What is the chemical process for the formation of an amino acid with its tRNA molecule?

A

amino acid activation

82
Q

Osteogenesis imperfecta and Ehler-Danlos(various) are disease associated with what type of collagen?

A

type I

84
Q

What is the mechanism which cause the following genetic diseases: mental retardation, microcephaly, wide-set eyes, and a characteristic kitten like cry?

A

terminal deletion of the short arm of chromosome 5

85
Q

What enzyme phosphorylates mannose residues in their oligosaccharide chains?

A

n-acetylglucosamine-1 phosphotransferase

86
Q

What is the biochemical defect causing scurvy? What are the major symptoms?(3-5)

A

Lack of vitamin C which is required for the enzymes lysyl hydroylase and prolyl hydroxylase. Major symptoms are petechiae, bleeding gums, ecchymoses loose teeth, poor wound healing and poor bone development

87
Q

α-thalassemia is a well-known example of a genetic disease in which what occurs?

A

unequal cross-over for one or more α-globin genes from chromosome 16

88
Q

How are codons written?

A

They’re written in the 5’ - 3’ direction

89
Q

What type of mutation: new codon specific different amino acid? What is the effect on protein?

A

missense mutation; possible decrease in function; variabele effects

91
Q

Generally speaking, how does a peptide bond formation occur?

A

The formation of a peptide bone takes pace between the carboxyl group of one amino acid and the amino group of another

92
Q

What is the A site and what is the P site?

A

The A site is the location for the upcoming aminoacyl tRNA in the ribosome. The “P” site is the site for the peptide bond formation during protein synthesis.

93
Q

What is the process of adding frankly or geranylgeranyl lipid groups to certain membrane-associated proteins?

A

prenylation; a co and posttranslational covalent modification

94
Q

Is it possible for multiple ribosomes to translate a message from mRNA molecule at the same time?

A

Yes

95
Q

What is the biochemical defect leading to Ehlers-Danlos syndromes?(2 points) What are the major symptoms?(4-8)

A

Mutation in collagen genes and lylsyl hydroxylase. Major symptoms are hyper mobility, hyperextensible, fragile skin, dislocation, varicose veins, ecchymoses, arterial, intestinal ruptures

97
Q

Psuedomonas and diphtheria toxin inhibit what part of protein synthesis?

A

eEF-2(which is found in prokaryotes) They inhibit ADP ribosylation

98
Q

What is a transition mutation?

A

It is a point mutation that replaces any purine-pyrimidine base pair with a purine-pyrimidine base pair

99
Q

How are defective copies of proteins properly discarded?

A

they marked for destruction by having multiple copies if ubiquitin. These proteins are directed to proteasomes for destruction.

100
Q

How does the genetic code vary across other species?(relative)

A

They don’t, the code is universal except for a few exceptions in the mitochondria

101
Q

What type of collagen: cartilage, vitreous humor?

A

type II

102
Q

What is the second stage in gene expression?

A

Translation the nucleotide sequence of a mRNA molecule into the amino acid sequence of a protein

103
Q

What is the mechanism of the mutation behind Huntingonton disease?

A

trinucleotide expansion, too many consecutive CAG coding for glutamine translating a very unstable protein

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