Nucleotides and Metabolism Quiz

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Questions and Answers

Which nitrogenous bases are classified as purines?

Guanine and Uracil

Adenine and Guanine (correct)

Thymine and Uracil

Adenine and Cytosine

What are the end products of pyrimidine degradation?

β-alanine, β-aminoisobutyrate, CO2, and NH3 (correct)

Uric acid and NH3

Guanine and uracil

Cytosine and thymine

Which function is NOT performed by nucleotides?

Mediate hormone action (cAMP, cGMP)

Serve as co-enzymes (NAD, FAD)

Store genetic information (correct)

Act as a source of energy (ATP, GTP)

What condition results from increased levels of uric acid in the blood?

Hyperuricemia Signup and view all the answers

What type of sugar is found in RNA nucleotides?

Ribose Signup and view all the answers

What sugar does RNA contain that differentiates it from DNA?

Ribose Signup and view all the answers

Which type of RNA is most abundant in the cell?

Ribosomal RNA (rRNA) Signup and view all the answers

How are eukaryotic ribosomes different from prokaryotic ribosomes?

Eukaryotic ribosomes have a higher S value. Signup and view all the answers

What is the main function of tRNA in protein synthesis?

To deliver amino acids to the ribosome. Signup and view all the answers

What characteristic structure does tRNA have?

Cloverleaf structure Signup and view all the answers

Which component of tRNA helps it to pair with mRNA during protein synthesis?

Anticodon loop Signup and view all the answers

Where is messenger RNA (mRNA) synthesized in eukaryotic cells?

In the nucleus Signup and view all the answers

What is the primary building unit of a single strand of DNA?

Polynucleotide sugar: deoxyribose Signup and view all the answers

Which of the following correctly describes the hydrogen bonding in double-stranded DNA?

C pairs with G via 3 hydrogen bonds Signup and view all the answers

Where is mitochondrial DNA primarily located?

Within the mitochondrial matrix Signup and view all the answers

Which statement correctly explains the difference between linear and circular DNA?

Linear DNA is characterized by linear arrangements in the nucleus, while circular DNA is found in the mitochondria. Signup and view all the answers

What type of bond links the mononucleotides in a single strand of RNA?

Phosphodiester bonds Signup and view all the answers

Which of the following statements about mitochondrial DNA is true?

It is a double-stranded circular DNA molecule. Signup and view all the answers

What is the primary structural difference between DNA and RNA?

DNA contains deoxyribose whereas RNA contains ribose. Signup and view all the answers

What occurs during the denaturation of DNA?

The breakdown of hydrogen bonds between the two strands. Signup and view all the answers

Study Notes

Nucleotides

Structure:
- Composed of a nitrogenous base, a sugar, and one to three phosphate groups.
- Nitrogenous bases:
  - Purines: Adenine (A), Guanine (G)
  - Pyrimidines: Thymine (T) - DNA only, Cytosine (C), Uracil (U) - RNA only
- Sugar:
  - Ribose (RNA)
  - Deoxyribose (DNA)
Functions:
- Building blocks:
  - RNA & DNA
- Energy: ATP & GTP
- Hormones: cAMP & cGMP are second messengers
- Coenzymes: NAD, FAD, Co-enzyme A

Nucleotide Metabolism

Synthesis (Anabolism):
- Purine ring atoms:
  - Derived from Glycine, Aspartate, Glutamine, CO2, and Tetrahydrofolate.
- Pyrimidine ring atoms:
  - Derived from Aspartate, Carbamoyl phosphate and Tetrahydrofolate.
Degradation (Catabolism):
- Purine rings:
  - Degraded to Uric acid
  - Excreted by the kidneys.
  - Hyperuricemia: High blood uric acid levels
  - Gout: A disease caused by uric acid deposition into joints and kidneys.
- Pyrimidine rings:
  - Degraded to β-alanine, β-aminoisobutyrate, CO2, and NH3

DNA

Importance:
- Genetic material: Stores and carries genetic information
- Replication:
  - Template for DNA synthesis, ensuring genetic information is passed onto new cells.
- Transcription:
  - Template for mRNA synthesis, allowing protein synthesis to occur.
Location:
- Eukaryotes: Nucleus and mitochondria
Structure:
- Single strand:
  - A polynucleotide chain of deoxyribose, phosphate groups, and nitrogenous bases (A, T, C, G).
  - Linked via phosphodiester bonds.
  - Two ends: 5' phosphate end and 3' hydroxyl end.
- Double stranded:
  - Two anti-parallel strands held together by hydrogen bonds between the bases.
  - A-T: Two hydrogen bonds
  - C-G: Three hydrogen bonds
- Tertiary structure:
  - In eukaryotes, DNA is packaged into chromosomes.
Types:
- Linear: Chromosomal DNA in eukaryotes.
- Circular:
  - Mitochondria (eukaryotes)
  - Prokaryotic chromosomes (nucleoid)
  - Plasmids (bacteria)
  - Plant chloroplasts

Mitochondrial DNA

Circular, double-stranded DNA molecule.
Maternally inherited:
- Only egg mitochondria are passed to a zygote.
High mutation rate:
- ~5-10 times higher than nuclear DNA.

RNA

General Structure:
- Polyribonucleotide chain:
  - Sugar, phosphate groups, and nitrogenous bases (A, U, C, G).
  - Linked via Phosphodiester bonds
- Single-stranded:
  - May fold into complex 3D structures.
- Linear:
  - Two ends: 5' phosphate and 3' hydroxyl end.
- Sugar: Ribose

RNA vs DNA

Key Differences:
- Sugar:
  - Ribose (RNA)
  - Deoxyribose (DNA)
- Bases:
  - Uracil (RNA)
  - Thymine (DNA)
- Structure:
  - Single-stranded (RNA)
  - Double-stranded (DNA)

Types of RNA

Ribosomal RNA (rRNA):
- Most abundant type of RNA.
- Function:
  - Found in ribosomes, responsible for protein synthesis.
- Location: Cytoplasm
Transfer RNA (tRNA):
- Structure:
  - Cloverleaf-shaped.
  - Contains modified bases (pseudouridine, dihydrouridine, ribothymidine).
  - Anticodon loop: Recognizes codons in mRNA.
  - CCA sequence: Carries amino acids.
- Function:
  - Deliver amino acids to the ribosomes during protein synthesis.
Messenger RNA (mRNA):
- Structure:
  - A linear molecule with a 5' cap and a 3' poly(A) tail.
- Synthesis: Transcription in the nucleus.
- Function:
  - Carries genetic information from DNA to ribosomes.
  - Guides protein synthesis.

Genetic Code

Sequence of bases in mRNA:
- Translated into the amino acid sequence of a protein.
Codon:
- Three consecutive bases on mRNA that code for one amino acid.
- Read in the 5' to 3' direction.
Total number of codons: 64
- 61: Code for the 20 common amino acids.
- 3: Stop codons (UAG, UGA, UAA) - Terminate protein synthesis.

Protein Synthesis (Translation)

Ribosomes:
- Eukaryotes: 80S (60S + 40S)
- Prokaryotes: 70S (50S + 30S)
Steps:
- Initiation:
  - Small ribosomal subunit binds to mRNA.
  - Initiator tRNA carrying methionine binds to the start codon (AUG).
  - Large ribosomal subunit joins the complex.
- Elongation:
  - tRNA carrying the next amino acid binds to the A site.
  - Peptide bond forms between the amino acids.
  - Ribosome moves along mRNA (translocation).
- Termination:
  - Stop codon in the mRNA is reached.
  - Release factors bind to the ribosome, releasing the polypeptide chain.
  - Ribosome subunits dissociate.
Elongation Factors:
- EF-Tu:
  - Helps tRNA bind to the ribosome A site.
- EF-Ts:
  - Recycles EF-Tu.
- EF-G:
  - Helps translocation of the ribosome along the mRNA.

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Description

Test your knowledge on the structure and functions of nucleotides as well as their metabolism. This quiz covers important concepts including the roles of nitrogenous bases, synthesis pathways, and degradation processes. Perfect for students studying biochemistry and molecular biology.