1
Q
Describe DNA molecules in prokaryotic cells.
A
- short
- circular
- not associated w histones (proteins)
- no introns
- contains 1 or more plasmids (small, circular DNA molecules)
2
Q
Describe DNA molecules in eukaryotic cells.
A
- long
- linear
- associated w proteins called histones
- has introns
- mitochondria + chloroplasts contain short, circular DNA not associated w proteins (similar to prokaryotic DNA)
3
Q
How is a chromosome formed?
A
- double helix of DNA is tightly wound around histones fixing it in position
- DNA-histone complex (chromatin) is then coiled
- coil is looped + further coiled, + then packed into chromosome which is stored in nucleus
4
Q
What is a gene?
A
- a specific sequence of DNA bases, that codes for an AA sequence of a polypeptide, or a functional RNA molecule (e.g. rRNA + tRNA)
5
Q
What is the role of genes?
A
- to control protein structure + function bc determines exact sequence of AAs during protein synthesis in a cell
6
Q
What is a locus (loci)?
A
- fixed position of a gene on a chromosome
7
Q
What is a triplet/codon?
A
- a sequence of 3 DNA/mRNA bases, which codes for 1 specific AA
8
Q
What are the 3 features of the genetic code?
A
- degenerate
- universal
- non-overlapping
9
Q
What does it mean by the genetic code being degenerate?
A
- multiple diff triplets can code for same AA, bc there’s 64 diff combinations of triplets (4^3) + only 20 diff AAs
- advantageous bc if a point mutation occurs, even if triplet of bases differ, it may still code for same AA + so has no effect
10
Q
What does it mean by the genetic code being universal?
A
- same triplet of bases, code for same AA in all organisms, bc have same base pairs (A,T,C,G)
- advantageous bc it means genetic engineering is possible
11
Q
What does it mean by the genetic code being non-overlapping?
A
- each base in a DNA sequence is read only once, + is part of only 1 triplet of bases that codes for 1 AA
- advantageous bc if point mutation occurs, it will only affect 1 triplet + so 1 AA
12
Q
What are start codons?
A
- triplet of bases, at start of every mRNA molecule, that codes for AA methionine, which is later removed from protein it it’s not needed for structure
13
Q
What are stop codons?
A
- triplet of bases, at end of every mRNA molecule, that codes for an AA marking end of a polypeptide chain, causing ribosome to detach + so stops translation
14
Q
What are introns?
A
- sections of DNA, within a gene, that don’t code for AAs + so polypeptide chains
15
Q
What are exons?
A
- sections of DNA, within a gene, that do code for AAs + so polypeptide chains, + are separated by 1 or more introns
