topic 4- DNA, Genes, Chromosomes Flashcards
What is a gene?
A base sequence of DNA which codes for the amino acid sequence of a polypeptide and functional RNA.
What is a locus?
The fixed position of a particular gene on a chromosome.
What is an allele?
Different version of the same gene.
What is a chromosome?
How DNA is stored. In eukaryotic cell’s nucleus DNA is stored a chromosomes.
What is a homologous pair?
a pair of chromosomes with the same size and genes, but may have different alleles.
Describe the structure of DNA molecules in eukaryotes.
Long, linear, and associated with proteins called histones.
How is DNA stored in eukaryotic cells to fit in the nucleus?
To tightly coil the DNA to fit in the nucleus as chromosomes, the DNA is tightly wound around proteins called histones.
Describe the structure of DNA molecules in prokaryotes.
Prokaryotes carry DNA also in chromosomes, but the DNA molecules are short, circular and not associated with proteins, instead it supercoils to fit into the the cell free in the cytoplasm.
Describe the structure of DNA molecules in chloroplast and mitochondria.
The DNA is similar to prokaryotic DNA, in that it is short, circular and not histone bound.
What are the 3 features of the genetic code?
Degenerate
Universal
Non overlapping
What are stop codons?
The final triplet of bases on the end of the mRNA that do no code for an amino acids. It used to tell the cell when to stop production of a protein.
What are start codons?
First triplet of bases at the start of the mRNA which tell the cell when to start protein production, but these code for a specific amino acid.
What is meant by the genetic code being degenerate?
Some amino acids are coded for by more than one triplet of bases, as the combinations of 64 possible triplets is more than is needed to code for 20 amino acids.
What is the advantage of the genetic code being degenerate?
If there was a point mutation, even though the triplet of bases will be, it may still code for the same amino acids therefore no effect.
What is meant by the genetic code being universal?
The same triplet of bases code for the same amino acids in all organism.
What is an advantage of the genetic code being universal?
It means genetic engineering is possible between different organisms. e.g. inserting human gene for insulin into bacteria
What is meant by the genetic code being non-overlapping?
Each bases in a gene is only part of one triplet of bases that code for an amino acid. Therefore each triplet of bases is read as a discrete unit.
What is an advantage of the genetic code being non-overlapping?
This is an advantage because if there was a point mutation it will only affect one triplet of bases and therefore one amino acids.
What are introns?
Sections of DNA which do not code of amino acids and therefore polypeptide chains.
Where are introns found?
Eukaryotic cell’s DNA.
When are introns removed, and why?
They are removed during protein synthesis so it doesn’t affect the amino acid order.
Which type of DNA does not have introns?
Prokaryotic DNA.
What are exons?
The sequence of bases which fo code for amino acids.
