Biological Chemistry Exam 1

A nucleotide differs from a nucleoside by the presence of which of the following?

Phosphate group

Which structural feature of RNA is primarily responsible for its decreased stability compared to DNA

Presence of 2’ hydroxyl group on ribose

Which statement best explains why purines must pair with pyrimidines in DNA

To maintain uniform diameter of the double helix

Which component of nucleotides carries the negative charge of DNA

Phosphate group

A researcher analyzes a nucleic acid sample and finds ribose sugars and uracil bases. Which molecule is most likely present?

mRNA

Which bond links nucleotides together in a nucleic acid strand?

Phosphodiester bond

Which nitrogenous base is classified as a pyrimidine?

Cytosine

In double-stranded DNA, which base pair forms three hydrogen bonds?

G-C

Which RNA type is directly responsible for bringing amino acids to the ribosome during protein synthesis?

tRNA

Which nitrogenous base is classified as a pyrimidine?

Cytosine

What is a Nucelotide?

Basic Building block (monomer) of (DNA and RNA)

3 components of a Nucleotide

Nitrogenous base, Pentose Sugar, Phosphate groups

What is a nucleoside

Base + Sugar only

What are Nitrogenous bases

Heterocyclic, aromatic molecules that contain N

Purines

Adenine (A)

Guanine (G)

Purines Structure

Fused 6-membered + 5-membered rings

Pyrimidines

Cytosine

Thymine → DNA only

Uracil → RNA only

Pyrimidines Structure

Single 6-membered rings

Phosphodiester bonds

Connects 3’ OH of one sugar to 5’ phosphate of next nucleotide

Form the sugar-phosphate backdown

Base pairings (Hydrogen Bonds)

A-T

G-C

Which base pair bonding is stronger?

G-C

Clinical Relevance

GC- rich regions are more stable

DNA replication, transcription, and repair depend on strand complementarity

mRNA

Codes for proteins

tRNA

Brings amino acids

rRNA

Forms ribosomes

Purine metabolism disorders

Gout (uric acid accumulation)

Cancer drugs

Blocks nucleotide synthesis

Antivirals

Nucleoside analogs interfere with viral replication

Essential amino acids must be obtained from the diet. Which of the following is essential?

Leucine

Which amino acid is aromatic, hydroxylated, and is important for enzyme regulation?

Tyrosine

Which amino acid is the precursor of serotonin and melatonin?

Tryptophan

Which of the following amino acids is positively charged at physiological pH?

Lysine

Which amino acid is non-chiral

Glycine

Which amino acid contains a sulfur atom that can form disulfide bonds?

Cytseine

Which amino acid is hydroxylated post-translationally to stabilize collagen

Proline

Which of the following is not a standard amino acid used in protein synthesis?

Ornithine

What kind of structure is this? Also what type? and which?

AA, positively charged, histidine

What kind of structure is this? Also what type? and which?

AA, Hydrophobic, Valine

LDL is considered “bad” because:

It deposits cholesterol in tissues

VLDL transports?

Lipids made in the liver

What is the main enzyme for lipid digestion?

Pancreatic lipase

Lipids include which of the following?

All of the above

High trans fat intake is linked to

Increased Cardiovascular disease

Which enzyme starts lipid digestion

Gastric lipase

If membrane lipids are modified to contain more saturated fatty acids, what happens to the membrane?

Increased rigidity

Saturated fatty acids

Have no double bonds

Omega fatty acids are classified by:

Position of first double bond from omega end

If a genetic mutation prevents proper formation of chylomicrons, which process is most impaired?

Transport of dietary lipids to tissues

Saturated fats pack tightly and are solid

True

What do we mainly eat

Lipids (like triglycerides)

What is the primary consequence of a bile obstruction (gallstones)

Decreased lipid emulsification

What is the role of bile?

Emulsify lipids

Lipids are absorbed in

Intestinal cells (enterocytes)

After absorption, lipids are packaged into:

Chylomicrons

Which is TRUE regarding lipid transport?

All of the above

Where are chylomicrons formed?

Intestinal cells

Where are VLDL produced?

Liver

What is VLDL

a type of "bad cholesterol" produced by your liver

What is LDL

low-density lipoprotein, is famous for carrying cholesterol,

What is VLDL’s job

transport triglycerides, which are fats your body uses for energy or stores as excess fat.

What is VLDL made of

mostly of triglycerides (about 50-60% of the particle).

What is HDL

good cholesterol, that acts like a cleanup crew, scooping up excess cholesterol from your bloodstream and taking it back to the liver to be broken down.

What is the main function of lipids?

Energy storage and membranes

What is a fatty acid?

A molecule with a carboxylic acid and hydrocarbon tail

Unsaturated fatty acids

Have at least one double bond?

Lipid digestion involves everything except?

DNA Polymerase

Which sequence best describes lipid transport after a high-fat meal

Intestine -> chylomicrons -> lymph -> blood

Where does lipid digestion begin?

Stomach

Omega-6 vs Omega-3 difference:

Position of double bond

What is the biochemical consequence of partial hydrogenation of vegetable oil?

Conversion to trans fats

Where do chylomicrons go first?

Lymphatic system

Omega-3 fatty acids:

Are associated with reduced heart disease

Fatty acids are:

Building blocks of lipids

Functions of lipids consist of everything except:

DNA replication

Elevated VLDL levels in metabolic syndrome are most likely caused by:

Increased liver synthesis of triglycerides

Chylomicrons transport:

Lipids from intestine

Which statement is correct?

Lipids are made of fatty acids

What is the expected physiological effect of increased omega-3 intake?

Reduced cardiovascular risk

Why is glycogen highly branched?

To allow faster synthesis and degradation

In glycogen synthesis, which molecule provides the energy to activate glucose?

UTP

What is the main role of glycogen breakdown in muscle cells?

To provide energy for muscle contractions

Why can the liver release free glucose into the blood but muscle cannot?

Muscle lacks glucose-6-phosphate

Epinephrine stimulates glycogen breakdown primarily during:

Stress or Exercise

Which hormone stimulates glycogen breakdown mainly in the liver during fasting?

Glucagon

What is the effect of insulin on glycogen metabolism?

Activates glycogen synthase

Which hormone predominates during the fed state?

Insulin

What unique function does glycogenin perform?

Self-glycosylates to start glycogen synthesis

What protein acts as the primer for glycogen synthesis?

Glycogenin

What is one advantage of glycogen branching?

Increases number of ends for metabolism

What is the function of the branching enzyme?

Create α-1,6 branches

What type of bonds are formed by glycogen synthase?

α-1,4

UDP-glucose serves as what during glycogen synthesis?

Activated glucose donor

Which enzyme activates glucose by forming UDP-glucose?

UDP-glucose pyrophosphorylase

During glycogen synthesis, glucose is first converted to which molecule?

Glucose-6-phosphate

Which activity of the debranching enzyme breaks the α-1,6 bond?

Isomerase

α-1,6 glucosidase

Which activity of the debranching enzyme moves three glucose residues to another chain?

Transferase activity

The glycogen debranching enzyme has how many enzymatic activities?

Two

Glycogen phosphorylase stops breaking glycogen when it is how many residues away from a branch point?

4

Which enzyme is the rate-limiting enzyme of glycogen synthesis?

Glycogen synthase