3.4.1 DNA, Genes and Chromosomes Flashcards
Q: How is DNA organized in prokaryotic cells?
A: In prokaryotic cells, DNA molecules are short, circular, and not associated with proteins.
Q: How is DNA organized in the nucleus of eukaryotic cells?
A: In the nucleus of eukaryotic cells, DNA molecules are very long, linear, and associated with proteins called histones. Together, a DNA molecule and its associated proteins form a chromosome.
Q: What are histones and what is their role in eukaryotic cells?
A: Histones are proteins associated with DNA in eukaryotic cells. They help in the packaging of DNA into a compact, organized structure known as chromatin, which forms chromosomes.
Q: Describe the DNA found in mitochondria and chloroplasts of eukaryotic cells.
A: The DNA found in mitochondria and chloroplasts of eukaryotic cells is short, circular, and not associated with proteins, similar to the DNA in prokaryotes
Q: Define a gene.
A: A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA, including ribosomal RNA (rRNA) and transfer RNA (tRNA).
Q: What is a locus?
A: A locus is the fixed position on a particular DNA molecule where a specific gene is located.
Q: What is a triplet in the context of DNA, and what does it do?
A: A triplet is a sequence of three DNA bases that codes for a specific amino acid.
Q: What does it mean that the genetic code is universal?
A: The genetic code is universal, meaning that the same triplet of DNA bases codes for the same amino acid in almost all organisms.
Q: What does it mean that the genetic code is non-overlapping?
A: The genetic code is non-overlapping, which means that each base in a DNA sequence is part of only one triplet, and each triplet is read in sequence, one after the other.
Q: What does it mean that the genetic code is degenerate?
A: The genetic code is degenerate, meaning that most amino acids are coded for by more than one triplet.
Q: In eukaryotes, does all nuclear DNA code for polypeptides?
A: No, in eukaryotes, much of the nuclear DNA does not code for polypeptides. There are non-coding multiple repeats of base sequences between genes.
Q: What are exons and introns within a gene?
A: Exons are sequences within a gene that code for amino acid sequences. Introns are non-coding sequences within a gene that separate the exons.
Q: How are genes structured in eukaryotic cells?
A: In eukaryotic cells, genes are structured with coding sequences (exons) that are separated by non-coding sequences (introns).
Describe the structure of a DNA molecule and explain how its structure is related to its functions.
Marking Points:
Double helix structure with two polynucleotide strands.
Hydrogen bonds between complementary base pairs (A-T and C-G).
Sequence of bases codes for amino acids in a polypeptide.
Stability due to strong phosphodiester bonds and base-pairing.
Ability to replicate accurately during cell division.
Compare the DNA in prokaryotic cells with that in eukaryotic cells.
Marking Points:
Prokaryotic DNA is circular, short, and not associated with histones.
Eukaryotic DNA is linear, longer, and associated with histone proteins.
Prokaryotic DNA is found in the cytoplasm (nucleoid region), whereas eukaryotic DNA is enclosed within the nucleus.
Presence of introns in eukaryotic genes, which are absent in prokaryotes.
