Chapter 4 Nucleic Acids Flashcards
What are the components of a nucleotide?
Phosphate, Pentose sugar, Nitrogen-containing bases
DNA contains deoxyribose; RNA contains ribose.
Which bases are classified as purines?
Adenine, Guanine
Purines have 2 nitrogen-containing rings.
Which bases are classified as pyrimidines?
Thymine, Cytosine, Uracil
Pyrimidines have 1 nitrogen-containing ring.
What is the function of adenosine triphosphate (ATP)?
Universal energy carrier, releases energy for metabolic activities
ATP can be hydrolyzed to ADP and AMP.
What is the structure of DNA?
Macromolecule, polymer of nucleotides, double stranded, helix
Synthesized during interphase, located in the nucleus in chromosomes.
What is a gene?
Length of DNA that codes for one or more polypeptide chains
Genes occupy a specific location on a chromosome called a locus.
What is the human genome composed of?
Approximately 25,000 genes
Some genes are also located in the mitochondria.
What stabilizes the DNA molecule?
Covalent bonds (phosphodiester bonds), histone coat
These provide strength and stability to the sugar-phosphate backbone.
Define complementary base pairing.
Specific pairing of nitrogenous bases ensuring identical sequences after replication
Errors are corrected by DNA polymerase.
What happens if one strand of DNA is damaged?
Information is not lost; the complementary strand can be used to rebuild it
This feature contributes to DNA’s stability.
What are Chargaff’s rules?
1) Number of one purine equals number of one pyrimidine; 2) Composition varies between species
A=T and C=G pairing ensures DNA is a constant width.
What is semi-conservative replication?
Each new DNA molecule retains one original polynucleotide strand
It produces identical sister chromatids prior to mitosis.
What did Meselson and Stahl’s experiment demonstrate?
DNA replication is semi-conservative
They used isotopes of nitrogen to distinguish between DNA densities.
What safety precautions should be taken when using ethanol for DNA purification?
Use ice-cold ethanol, avoid spark-prone environments
Ethanol vapors can be flammable and lead to explosions.
What is a mutation?
Spontaneous change in the quantity or arrangement of DNA
This includes changes in the nucleotide sequence of the genome.
What are mutagens?
Substances that cause mutations, e.g., tar, mustard gas, radiation
They can induce changes during DNA replication.
What is the definition of mutations?
Spontaneous or random change in the quantity or arrangement of DNA, i.e., change in the nucleotide sequence of the genome.
What can cause mutations?
Mutagens such as tar, mustard gas, benzene, or radiation: UV light, X-rays, gamma rays.
When do mutations occur?
They occur randomly during DNA replication in interphase.
What are somatic mutations?
Mutations that occur during mitosis, leading to aging and cancer.
How do mutations in gametes differ from somatic mutations?
Gamete mutations can be inherited and occur during meiosis, affecting future generations.
What are chromosome mutations?
Changes to the structure (whole or part) of a chromosome, including deletion(s), insertion(s), or translocation(s).
Define DNA point mutations.
Changes to the structure of a gene due to a change in the nucleotide base sequence.
What is a substitution mutation?
Occurs when one base is substituted for another, potentially affecting only 1 triplet.
What is a deletion mutation?
Removal of one or more bases, causing a frameshift and affecting many triplets.
What is an insertion mutation?
Addition of one or more bases, causing a frameshift and affecting many triplets.
What happens to codons after an insertion or deletion of a base?
Codons after the insertion/deletion will all be altered, potentially leading to a truncated polypeptide or a new sequence of amino acids.
Do point mutations always affect protein function?
No, because each amino acid is coded for by more than one codon and the code is degenerate.
What is the biological importance of mutations?
Mutations contribute to evolution, cancer, and immune system development.
Give an example of a beneficial mutation.
Production of melanin in early humans in Africa for UV protection and vitamin D synthesis.
What is the triplet code in the genetic code?
A sequence of 3 nucleotide bases called a codon, where each codon codes for one specific amino acid.
What is meant by a degenerate code?
All amino acids (except methionine) have more than one codon.
What does it mean that the genetic code is non-overlapping?
Each base is only part of one codon, with each triplet read separately.
What are the two main types of nucleic acids?
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
What are the functions of DNA?
Carries genetic information, consists of introns and exons, codes for specific polypeptides.
What is the structure of mRNA?
Carries the same sequence of nucleotide bases as the coding strand of DNA, but with uracil instead of thymine.
What is the role of tRNA?
Carries specific amino acids to ribosomes according to its anticodon.
What is the function of ribosomal RNA (rRNA)?
Forms the ribosome’s subunits and acts as an enzyme to join amino acids during translation.
What are the key differences between DNA and RNA?
DNA is double-stranded, contains deoxyribose and thymine; RNA is single-stranded, contains ribose and uracil.
What is transcription?
The synthesis of a mRNA molecule with a complementary sequence to a section of DNA.
What occurs during transcription?
RNA polymerase synthesizes mRNA in the nucleoplasm, unwinding DNA and adding RNA nucleotides.
What is alternative splicing?
The process of joining exons together in different combinations to form mature mRNA.
What is the purpose of translation?
Production of a specific polypeptide chain from the code sequence of mRNA at ribosomes.
What is the first codon in mRNA during translation?
AUG, which codes for the amino acid methionine.
What is the role of ribosomes in translation?
Site where mRNA is read and polypeptide chains are synthesized.
What is the function of peptidyl transferase?
Catalyzes the formation of peptide bonds between adjacent amino acids during translation.
What are anticodons?
Sequences of 3 exposed RNA-nucleotides on tRNA specific for one amino acid.
What are codons?
Sequences of 3 nucleotide bases found on mRNA and DNA.
