HY USMLE Q #495 – Biochemistry — Transcript

Full transcript

1. 0:00how's it going guys we have a past level
2. 0:01question for biochemistry for step one
3. 0:04okay i know some of these answer choices
4. 0:06might look a bit confusing but this is
5. 0:08considered a bread and butter
6. 0:10important question no excuses so before
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10. 0:16me on instagram at melbourne underscore
11. 0:18medical mehl at man underscore medical
12. 0:20links down below find me on telegram
13. 0:22links the telegram group and channel are
14. 0:23down below don't start the clip
15. 0:24four-year-old boy he has a history of
16. 0:26fractures and our image shows us blue
17. 0:28sclera okay i mean this is a
18. 0:31high yield diagnosis past level as i
19. 0:33said for
20. 0:34osteogenesis imperfecta okay it's a
21. 0:37collagen one defect so let's just block
22. 0:40the dance choice here we'll go backwards
23. 0:41choice impaired desmosine crosslinking
24. 0:43wrong [ __ ] answer this in theory
25. 0:45would refer to an elastin problem okay
26. 0:48you could be aware that desmozine is a
27. 0:50protein within elastin okay unlike
28. 0:54collagen it does not have a glycine xy
29. 0:57primary structure it does not form a
30. 1:00triple helix it does not contain
31. 1:02carbohydrate okay so
32. 1:04uh elastin defect could refer to in
33. 1:07theory williams syndrome autosomal
34. 1:09dominant chromosome seven uh
35. 1:11supravalvular aortic stenosis elephant
36. 1:13like faces hypercalcemia vitamin d
37. 1:16hypersensitivity
38. 1:17wrong [ __ ] answer
39. 1:20choice d gtpa's constitutive activity
40. 1:22wrong answer could refer to in theory
41. 1:25cross k-r-a-s mutated some colon cancers
42. 1:29where uh constitutive activity means
43. 1:31it's always on you need to cleave gtp
44. 1:33into gdp to shut off gtp aces and you
45. 1:36can't do that in crass wrong [ __ ]
46. 1:38answer should i see like a protein
47. 1:40forming disserate sheets around a last
48. 1:42and wrong answer you need to know that
49. 1:44marfan syndrome which codes for uh or to
50. 1:47defect in fiberline autosomal dominant
51. 1:48chromosome 15 fpn1 fbn2 you need to know
52. 1:51fiberlin is a glycoprotein that forms a
53. 1:54sheath around elastin okay nothing to do
54. 1:56with collagen i want you to memorize
55. 1:57that fibrillin is a glycoprotein that
56. 2:00forms a sheath around elastin there's an
57. 2:01old nvme exam for step one nbme 12 or 13
58. 2:06one of the old forms where they asked
59. 2:08about marfin syndrome the answer was
60. 2:09literally quote uh glycoprotein that
61. 2:11forms a sheath around elastin that's
62. 2:14fibrillin wrong [ __ ] answer
63. 2:16choice b glycemic tryptophan
64. 2:18substitution is correct okay so this is
65. 2:20osteogenesis and perfect as i said uh
66. 2:22defect in collagen one this is not the
67. 2:24only potential mechanism for oa for oi
68. 2:28nor does the usmle actually give a [ __ ]
69. 2:31okay don't worry about omg this specific
70. 2:35glycemic return substitution it's not
71. 2:36that it's just this is the only answer
72. 2:39that refers to
73. 2:41collagen in this case they could have
74. 2:43had an answer such as impaired
75. 2:45hydroxylation of collagen residues or
76. 2:47impaired glycosylation of collagen
77. 2:49residues or impaired formation of the
78. 2:51triple helix collagen residues impaired
79. 2:54ability to cleave the
80. 2:56non-triple helix end groups from
81. 3:00exocytosed collagen okay so
82. 3:02people get pulled into it's the force
83. 3:04for the trees type of thing people get
84. 3:06pulled into these nitpicky mechanisms
85. 3:08when in reality it's just this is the
86. 3:10only one that could explain a defect in
87. 3:12collagen in this case okay so you can
88. 3:15get conductive hearing loss uh impaired
89. 3:17formation of the ossicles the middle ear
90. 3:19bones
91. 3:20and blue sclera classic fractures at
92. 3:23different stages of healing
93. 3:25and often mistaken for child abuse you
94. 3:27have to think of differentials
95. 3:29such as albers schoenberg syndrome
96. 3:31that's osteoporosis okay in child abuse
97. 3:33as i said uh and it can be there's
98. 3:35different types of oi okay if you were
99. 3:37to wiki you're like wow there's like
100. 3:39eight to twelve types however many
101. 3:40differing severities okay it can be
102. 3:43fatal in utero as well for harder
103. 3:45questions they can mention a woman who's
104. 3:46had a prior miscarriage okay and the
105. 3:49implication being maybe there was a
106. 3:51variant somehow of the oi where it was
107. 3:53worse in utero okay so let's just whip
108. 3:55the last answer choice desmoglian
109. 3:57binding of calcium wrong answer this in
110. 3:59theory could refer to pemphigus vulgaris
111. 4:02okay desmoglian is a protein in
112. 4:05uh desmosomes okay and desmoglian is
113. 4:08part of the cad herein family of
114. 4:12connective tissue molecules
115. 4:14so that would catherines are calcium
116. 4:17dependent okay
117. 4:18so whereas of course uh boles typhoid
118. 4:21hemidesmosomes
119. 4:23you know the deal and to make more
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122. 4:28that's it