DNA and RNA Structure
what are the three main components of a nucleotide?
A nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and a phosphate group
During which phase of the cell cycle does DNA replication occur?
It occurs during the S phase (Synthesis phase) of Interphase.
What is the primary goal of meiosis compared to mitosis?
Meiosis produces four genetically unique haploid cells (gametes) for sexual reproduction, while mitosis produces two identical diploid cells for growth and repair.
What is the difference between a point mutation and a frameshift mutation?
A point mutation changes a single nucleotide base (substitution), while a frameshift mutation is an insertion or deletion that shifts the entire "reading frame" of the genetic code, usually changing every amino acid that follows.
What are enzymes, and what is their primary function?
Enzymes are biological catalysts (mostly proteins) that speed up chemical reactions by lowering the activation energy required for the reaction to occur.
How do the sugars in DNA and RNA differ?
DNA contains deoxyribose, which lacks one oxygen atom on the second carbon, while RNA contains ribose, which has a hydroxyl (-OH) group on that carbon.
What is the function of the enzyme Helicase?
It unzips the DNA double helix by breaking the hydrogen bonds between the nitrogenous bases, creating a replication fork.
What happens during "Crossing Over," and when does it occur?
Homologous chromosomes exchange segments of DNA during Prophase I, which increases genetic variation in offspring.
What is a "silent mutation"?
A substitution that changes a codon to another codon that codes for the same amino acid, resulting in no change to the final protein.
How does the "Lock and Key" model describe enzyme action?
It suggests that the substrate (the key) has a specific shape that fits perfectly into the active site (the lock) of the enzyme.
Which nitrogenous bases are found in DNA versus RNA
Both have Adenine, Guanine, and Cytosine. However, DNA uses Thymine, while RNA replaces it with Uracil.
In which direction is a new DNA strand always synthesized?
It is always synthesized in the 5' to 3' direction.
How does the chromosome number change from the start to the end of meiosis?
It is reduced by half (from diploid, 2n, to haploid, n). In humans, a cell with 46 chromosomes divides to produce cells with 23.
How does a "nonsense mutation" affect protein synthesis?
It changes an amino acid codon into a stop codon, causing translation to end prematurely and usually resulting in a nonfunctional, shortened protein.
What does it mean when an enzyme is "denatured"?
The enzyme's 3D shape is permanently altered—usually by high temperature or extreme pH—making the active site non-functional and the enzyme unable to bind to its substrate.
What is the structural difference between the strands of DNA and RNA?
DNA is typically double-stranded (forming a double helix), whereas RNA is usually single-stranded.
What are Okazaki fragments, and on which strand are they found?
They are short segments of DNA synthesized discontinuously on the lagging strand because DNA polymerase can only work in one direction.
What is "Independent Assortment," and in which phase does it happen?
It is the random alignment and separation of homologous chromosome pairs during Metaphase I, ensuring each gamete has a unique mix of maternal and paternal genes.
What is a "missense mutation"?
A substitution that results in a different amino acid being placed in the protein chain, which can change the protein's shape and function (e.g., Sickle Cell Anemia).
What is the "Induced Fit" model?
A more accurate version of the lock and key model where the active site slightly changes shape to grip the substrate more snugly once it bind
What type of bond holds the two strands of a DNA molecule together?
Hydrogen bonds between the complementary nitrogenous bases (A with T, and C with G).
Why is DNA replication described as "semi-conservative"?
Because each new DNA molecule consists of one original (parental) strand and one newly synthesized strand.
What is the difference between Anaphase I and Anaphase II?
In Anaphase I, homologous chromosomes are pulled to opposite poles; in Anaphase II, sister chromatids are pulled apart.
What are some common causes of mutations (mutagens)?
External factors like UV radiation, X-rays, and certain chemicals, as well as internal errors during DNA replication
How do inhibitors affect enzyme activity?
Competitive inhibitors block the active site by mimicking the substrate, while non-competitive inhibitors bind elsewhere on the enzyme (the allosteric site), changing the active site's shape so the substrate can no longer fit.