Biochemistry Test (Part 1)
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1) Which of the following factors shifts the oxygen dissociation curve to the left?
Explanation: The following shift the oxygen dissociation curve to the right: Increased temperature Increased H+ (i.e. acidosis) Increased 2,3 DPG Increased pCO2 The following shift the oxygen dissociation curve to the left: Increasing pCO shifts the curve to the left Decreased temperature Decreased [H+] (alkolosis) Decreased 2,3 DPG The Oxygen Dissociation Curve for fetal haemoglobin lies to the left of the normal adult Oxygen Dissociation Curve as it has a higher affinity for Oxygen.
2) You see a diabetic women in preconception clinic. Which of the following is appropriate advice regarding folic acid supplementation?
Explanation: Standard dose is 400mcg daily until week 12 In pregnant women 5mg daily until week 12
3) Which of the following bases does Cytosine pair with?
Explanation: Amino acids Amino acids are coded for by nucleotides. Typically a series of 3 nucleotides (termed a codon) code for a single amino acid. A nucleotide is made of a nitrogenous base, sugar (ribose or 2‐deoxyribose depending on if it is DNA or RNA) and phosphate. Nucleotides contain either a purine or a pyrimidine base. Ribonucleotides are nucleotides in which the sugar is ribose. Deoxyribonucleotides are nucleotides in which the sugar is deoxyribose. PASS‐MRCOG | Bio‐Chemistry In DNA, the purine bases are adenine and guanine, while the pyrimidines are thymine and cytosine. RNA uses uracil rather than thymine.
4) In times of starvation which ketone body listed below can be utilised by the heart for energy?
Explanation: Remember there are 3 endogenous ketone bodies. Only 2 are listed (Acetone and Beta‐hydroxybutyric acid) and only the later of the 2 listed is used for energy. Acetoacetic acid is the other endogenous ketone body. Acetoacetic acid and Beta‐hydroxybutyric acid can be utilised by the brain, heart and muscles in states of carbohydrate restriction e.g. starvation.
5) What is the main extracellular Cation?
Explanation: Knowledge of basic biochemistry is a requirement
6) Which of the following organelles is responsible for fusing with vesicles and modifying the proteins contained within them?
Explanation: The Golgi Apparatus or Golgi Complex fuses with vesicles containing proteins secreted by the ER. It modifies them and packages them for other destinations within the cell. The Golgi can be thought of as the Post Office of the cell.
7) What is the main biochemical buffer in urine?
Explanation: Phosphate and ammonia are the major urinary buffers
8) What is the main plasma Cation?
Explanation: Remember the major cations and anions are the same for plasma and extracellular fluid
9) Which of the following factors shifts the oxygen dissociation curve to the right?
10) A 28 year old women is seen in the early pregnancy unit. She has had a positive pregnancy test but is uncertain of her LMP. Ultrasound doesn't visualise a pregnancy. You perform bHCG tests 48 hours apart. The first bHCG is 400mIU/ml. The second is 190mIU/ml. What is the likely diagnosis
Explanation: hCG has dropped by >50%. This is consistent with non‐viable pregnancy. In the exam you may also be given a progesterone as a clue, progesterone <20nmol/l is consistent with non‐viable pregnancy. Note NICE advice is progesterone shouldn't be used as an adjunct. You should be able to work out if the pregnancy is viable or non‐viable by the hCG measurements alone. In the exam you are unlikely to be given a scenario in the midrange i.e. hCG between 50% drop and 63% rise as there are multiple possible diagnoses attributed to this.
11) What of the following is a major biochemical buffer in intracellular fluid (ICF)?
Explanation: Proteins and phosphate are the major buffers of ICF
12) Which cell adhesion molecules are dependent on calcium ions to function?
Explanation: Cadherins are calcium ion dependent adhesion molecules. Kindlin‐1 and Kindlin‐2 activate integrins. The selectins are also cell adhesion molecules,there are three types: E‐selectin (in endothelial cells) L‐selectin (in lymphocytes) P‐selectin (in platelets)
13) What is the main intracellular Cation?
14) With regard to the cell cycle. In which part of the cycle do Chromatids form?
15) What does NICE advise pregnant diabetic women should keep their HBA1C below?
Explanation: 6.1% is the old target from NICE guideline 63. This guidance was replaced by NICE guideline 3 in February 2015. The current recommendation is to keep HBA1C below 6.5% or 48mmol/mol
16) Which of the following is used in protein analysis?
Explanation: Northern and Southern blotting are molecular genetic techniques to detect RNA and DNA sequences respectively Southwestern blotting measures DNA binding proteins Eastern blotting measures protein modificatons e.g. lipids or carbohydrates
17) Which of the following is used in RNA analysis?
Explanation: Northern and Southern blotting are molecular genetic techniques to detect RNA PASS‐MRCOG | Bio‐Chemistry and DNA sequences respectively Southwestern blotting measures DNA binding proteins Eastern blotting measures protein modificatons e.g. lipids or carbohydrates
18) With regard to the cell cycle. At what stage do the chromosomes align on the equatorial plane?
Explanation: G0 is a resting phase. Interphase (G1,S,G2) is where the cell grows and DNA replication occurs forming chromatids. Mitosis is where cell division occurs and this happens in a the following phases: Prophase Chromatin condenses to chromosomes (paired as chromatids). Mitotic spindle forms Metaphase Chromatids align at the equatorial plane AKA the metaphase plate Anaphase Chromotids pulled apart into 2 constituent daughter chromosomes Telophase New nuclear envelopes form around each daughter chromosome Cytokinesis Cells divide
19) Which is the most important ion for generating resting membrane potential (in non excitable cells)?
Explanation: The resting membrane potential of a cell arises from the potential between potassium ions from intracellular fluid and anions across the membrane of the cell. Because membrane permeability to potassium is higher than for other ions potassium ions flow from ICF to ECF carrying positive charge until their movement is balanced by build‐up of negative charge on the inner surface of the membrane.
20) With regard to the cell cycle. In which part of the cycle does DNA replication occur?
Explanation: DNA replication occurs during S phase but that isn't one of the options. Remember Interphase comprises G1,S and G2 phases!
21) What biochemical process utilises pyruvate to form ATP?
Explanation: This is the Krebs or Citric Acid Cycle. The Calvin cycle is a process related to photosynthesis in plants, algae and certain bacteria.
22) Which of the following organelles is responsible for holding mRNA for translation into protein
Explanation: The Ribosome holds the mRNA and translates the appropriate protein.
23) A 28 year old women is seen in the early pregnancy unit. She has had a positive pregnancy test but is uncertain of her LMP. Ultrasound doesn't visualise a pregnancy. You perform bHCG tests 48 hours apart. The first bHCG is 400mIU/ml. The second is 690mIU/ml. What is the likely diagnosis
Explanation: In normal pregnancy hCG levels should rise by around 66% every 2 days. NICE advise >63% rise consistent with likely viable intrauterine pregnancy. In the example above there has been a 72% rise in 2 days ‐ consistent with viable pregnancy. In the exam if you are asked to interpret 2 hCG results you are likely to be given either viable or non‐viable pregnancy scenarios as ectopic/molars/multigestation shouldn't be diagnosed from hCG (+/‐ progesterone) results alone. In molar pregnancy a very high hCG is typically seen. In partial molar pregnancy the hCG typically rises at a slower rate and to a lower level than seen in normal pregnancy. In ectopic pregnancy hCG levels tend to plateau or have a doubling time of greater than 7 days (doubling time 3 days in normal pregnancy) In twin pregnancies hCG levels are typically higher than for single intrauterine pregnancy
24) You see a 55 year old lady in menopause clinic. Taking a history she tells you she gets general aches and pains and has been worried about diabetes as she is constantly thirsty. Otherwise she has no significant past medical history and is on no regular medication. You organise bloods and the results are below. What is the likely diagnosis?
Na 135 mmol/l K3.8 mmol/l Ur 7.6 mmol/l Cr 82 mmol/l ESR 15 mm/h PTH 80 pg/ml (HIGH) HBA1C 38 mmol/mol Adjusted calcium 2.76 mol/l (HIGH)
Explanation: High PTH with hypercalcaemia is seen in Primary Hyperparathyroidism.Although tumours of the parathyroid occur in MEN, parathyroid adenoma accounts for 97% of cases of primary hyperparathyroidism. High PTH with hypercalcaemia is also seen in tertiary hyperparathyroidism. Tertiary hyperparathyroidism usually follows a long period of secondary hyperparathyroidism (most commonly due to renal failure). This patient has no medical history of being unwell or having had a long period of renal impairment.
25) What is the role of DHEA produced by the fetal adrenal glands?
Explanation: Dehydroepiandrosterone (DHEA) is a steroid hormone synthesised from cholesterol (via Pregnenolone) by the adrenal glands. The fetus manufactures DHEA, which stimulates the placenta to form estrogen, thus keeping a pregnancy going. Production of DHEA stops at birth, then begins again around age seven and peaks when a person is in their mid‐20s
26) What is the main biochemical buffer in blood?
Explanation: Bicarbonate is the main buffer in blood.
27) You see a patient on the ward and perform an ABG. The results are as follows
pH 7.25 pO2 8.6 kPA pCO2 8.0 kPa Base Excess +2 What is the acid base disturbance?
Explanation: This patient has acidosis as the pH is <7.35 The pO2 is irrelevant.The pCO2 is low i.e. the respiratory system is trying to alkalise. The patient is acidotic however so this is compensatory. Clinically the patient is "blowing off" CO2 and clinically would be tachypneic. The Base Excess is negative i.e. the metabolic system is causing acidosis and the patient is acidotic. This is a metabolic acidosis.
28) A patient is seen in the gynaecology outpatient clinic and is noted to have large volume genital warts perianally and near the urethral meatus. You discuss treatment options and the patient opts for LASER therapy. Which of the following is the most appropriate type of LASER to use?
Explanation: For the exam the RCOG syllabus expects you to be familiar with uses of LASER. You are most likely to be asked therefore about procedures where there is consensus about the optimal laser choice and this is currently limited to: 1. Pre cancerous lower genital tract changes (CIN) and condylomata (HPV) ‐ Choose CO2 laser* 2. Laser ablation in TTTS ‐ Choose Diode or ND:YAG *This isn't to imply LASER is 1st line treatment for CIN or genital warts but rather if LASER is chosen then CO2 is the preferred Laser type
29) The COCP (Combined Oral Contraceptive Pill) causes all of the following biochemical effects EXCEPT which one?
Explanation: Remember patients with PCOS have elevated LH. COCPs suppress synthesis and secretion of FSH and the mid‐cycle surge of LH, thus inhibiting the development of ovarian follicles and ovulation COCPs reduce hyperandrogenism as reduced LH secretion re sults in decreased ovarian synthesis of androgens. Furthermore they stimulate the liver to produce Sex Hormone Binding Globulin which leads to decreased circulating free androgens. Other mechanisms include reduction in adrenal androgen secretion and inhibition of peripheral conversion of testosterone to dihydrotestosterone and binding of dihydrotestosterone to androgen receptors
30) In the foetus where is the principle site of alpha fetoprotein (AFP) production
Explanation: Fetal AFP is principally produced in the Liver. Other sites of production are the GI tract and the Yolk Sac.
31) Where in the body are ketone bodies produced during times of starvation
Explanation: Ketone bodies are produced by the Liver.
32) Which of the following proteins is a major tumour suppressor?
Explanation: P53 is a protein that is encoded by the TP53 gene in humans. TP53 gene is located on the short arm of chromosome 17. It has been dubbed the "guardian of the genome" as it suppresses tumour formation and therefore cancer by preventing genome mutation. P53 inactivation or mutation is essential for the formation of the majority of human cancers.
33) Which of the following is used in protein analysis?
34) With regard to the cell cycle. In what phase do chromatids get cleaved into chromosomes and pulled apart?
Explanation: G0 is a resting phase. Interphase (G1,S,G2) is where the cell grows and DNA replication occurs forming chromatids. Mitosis is where cell division occurs and this happens in a the following phases: Prophase Chromatin condenses to chromosomes (paired as chromatids). Mitotic spindle forms Metaphase Chromatids align at the equatorial plane AKA the metaphase plate Anaphase Chromotids pulled apart into 2 constituent daughter chromosomes Telophase New nuclear envelopes form around each daughter chromosome Cytokinesis Cells divide Diagram illustrating Mitosis
35) With regard to the cell cycle. In what phase do nuclear envelopes form around daughter chromosomes?
Explanation: G0 is a resting phase. Interphase (G1,S,G2) is where the cell grows and DNA replication occurs forming chromatids. Mitosis is where cell division occurs and this happens in a the following phases:
Prophase Chromatin condenses to chromosomes (paired as chromatids). Mitotic spindle forms Metaphase Chromatids align at the equatorial plane AKA the metaphase plate Anaphase Chromotids pulled apart into 2 constituent daughter chromosomes Telophase New nuclear envelopes form around each daughter chromosome Cytokinesis Cells divide Diagram illustrating Mitosis
36) Vitamin K is essential for the synthesis of
Explanation: Vitamin K Vitamin K is a fat soluble vitamin that is stored in the liver and adipose tissues. Other fat soluble vitamins are A, D and E. PASS‐MRCOG | Bio‐Chemistry It is essential for the synthesis of: ‐ Clotting factors (X)10,(IX) 9, 7(VII), 2 (II) (pneumonic 1972) ‐ Proteins C, S and Z ‐ Osteocalcin and GLA proteins
37) You see a patient on the ward who is acutely short of breath and perform an ABG. The results are as follows
Explanation: This patient has acidosis as the pH is low <7.35 The pO2 is irrelevant.The pCO2 is raised i.e. the respiratory system is causing acidosis. The patient is acidotic so this is a respiratory acidosisThe Base Excess is normal. You would typically expect the base excess to rise but metabolic compensation is slower than respiratory compensation so this picture may be seen acutely
38) Which of the following are cell adhesion molecules that bind leucocytes?
Explanation: Cadherins are calcium ion dependent adhesion molecules. Fibronectin is one of the integrins. The selectins are also cell adhesion molecules,there are three types: E‐selectin (in endothelial cells) L‐selectin (in lymphocytes) P‐selectin (in platelets)
39) What biochemical process utilises pyruvate to form ATP?
40) You see a 77 year old lady in clinic due to postmenopausal bleed. Pelvic ultrasound shows no evidence of malignancy and speculum examination is unremarkable. You are handed bloods and the results are below. What is the likely diagnosis?
Na 135 mmol/l K5.5 mmol/l Ur 10.6 mmol/l (HIGH) Cr 138 mmol/l (HIGH) ESR 28 mm/h (HIGH) PTH 80 pg/ml (HIGH) HBA1C 38 mmol/mol Adjusted calcium 2.06 mol/l (LOW)
Explanation: This is secondary hyperparathyroidism. The PTH is high in response to hypocalcaemia. Hypocalcaemia is likely secondary to renal failure ‐ the most common cause of secondary hyperparathyroidism.
41) Which nucleotide is unique to RNA?
Explanation: Uracil is found in RNA not DNA Thymine is found in DNA not RNA
42) Which nucleotide is unique to DNA?
43) A diabetic women attends your preconception clinic. You have checked her HBA1C. According to NICE guidelines what HBA1C level would prompt you to strongly advise this women NOT to get pregnant due to the signifiant risks it presents?
Explanation: Patients with HBA1C of 10.0% or greater should be strongly advised to use contraception and improve glycemic control prior to getting pregnant.
44) What is the role of DHEA produced by the fetal adrenal glands?
45) Which of the following organelles is responsible for protein folding and is studded with ribosomes?
Explanation: The ER is responsible for protein storage and folding. The rough ER is so called due to its appearance ‐ the ribosomes studding its surface giving a rough appearance.
46) Which of the following organelles is responsible for protein folding and is studded with ribosomes?
47) Fibrinogen is activated by which of the following?
Explanation:
Diagram illustrating coagulation pathway
48) In times of starvation which ketone body listed below can be utilised by the heart for energy?
49) A 28 year old women is seen in the early pregnancy unit. She has had a positive pregnancy test but is uncertain of her LMP. Ultrasound doesn't visualise a pregnancy. You perform a progesterone test. The result is 59 nmol/l. According to NICE guidelines what level is consistent with viable pregnancy?
Explanation: NICE state progesterone levels shouldn't be used to diagnose viable or ectopic pregnancy. PASS‐MRCOG | Bio‐Chemistry RCOG suggest levels >60 are consistent with viable pregnancy and you may get a progesterone level in a clinical scenario but not usually without serial hCG measurements. This may seem like a trick question but highlights that if you get a question on pregnancy of unknown location then the clinical picture is of primary importance followed by hCG
50) What biochemical process produces pyruvate from glucose?
Explanation: Glycolysis produces pyruvate which then enters the Krebs cycle (AKA the citric acid cycle)
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