DNA Structure & Rules
What are the four nitrogen bases found in DNA?
Adenine, Thymine, Cytosine, Guanine
What is the main goal of DNA replication?
To make an identical copy of DNA before cell division
What is transcription?
Making an RNA copy of a gene
What is a mutation?
a change in the DNA sequence
Why do multicellular organisms need cell division?
Growth, repair, and replacement of cells
Which base pairs with cytosine in RNA?
guanine
What enzyme separates the two strands of DNA?
Helicase
Where does transcription occur in eukaryotic cells?
nucleus
Are all mutations harmful? Why or why not?
No; some are silent or occur in non-coding DNA
During which phase is DNA copied?
S phase
What does it mean when DNA strands are described as antiparallel?
They run in opposite directions (one 5′→3′, the other 3′→5′)
Why does DNA replication need primers?
DNA polymerase cannot start synthesis on its own
What is the role of mRNA?
It carries instructions from DNA to the ribosome
What is one possible cause of mutations?
Errors during replication or environmental factors (radiation, chemicals)
What is the purpose of cell cycle checkpoints?
To ensure DNA is accurate and conditions are safe before division
Why are hydrogen bonds important in DNA?
They hold base pairs together and stabilize the double helix
Why is one strand made in fragments during replication?
DNA polymerase can only build in one direction (5′→3′)
Why are codons always read in groups of three?
Each group of three bases codes for one amino acid
Why can insertions or deletions be more harmful than point mutations?
They can shift the reading frame of the gene
What might happen if checkpoints fail?
Damaged cells may divide, leading to uncontrolled growth
Why does DNA’s base sequence matter more than its shape?
The sequence stores genetic information that determines proteins
How does proofreading help prevent problems in cells?
It reduces mutations by fixing mistakes during replication
Why is AUG an important codon?
It signals the start of translation and codes for methionine
How can a mutation in DNA affect an organism’s traits?
It can change a protein’s shape or function, affecting cell behavior
Why is p53 sometimes called the “guardian of the genome”?
It can stop the cell cycle or trigger apoptosis when DNA is damaged