4.1 DNA, genes and chromosomes Flashcards
Compare DNA in eukaryotic cells with DNA in prokaryotic cells (3)
● Nucleotide structure is identical - deoxyribose attached to phosphate and a base
● Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds
● DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes
○ Short, circular, not associated with proteins
Contrast DNA in eukaryotic cells with DNA in prokaryotic cells (4)
● Eukaryotic DNA is longer Prok is shorter
● Eukaryotic DNA is linear, prokaryotic DNA is circular
● Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
● Eukaryotic DNA contain introns, prokaryotic DNA does not
What is a chromosome
*Long Linear DNA that is associated with histones
*In the nucleus of eukaryotic cells
What is a gene (3)
*A sequence of DNA bases that code for
* the amino acid sequence of a polypeptide
*Or a functional RNA (e.g. Ribosomal RNA or tRNA)
What is a locus
Fixed position of a gene occupies on a particular DNA molecule
Describe the nature of the genetic code (4)
Triplet code: A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
Universal: The same base triplets code for the same amino acids in all organisms
Non-overlapping: Each base is part of only one triplet so each triplet is read as a discrete unit
Degenerate: An amino acid can be coded for by more than one base triplet
What are non coding base sequences and where are they found
Non coding sequence-DNA that does not code for amino acid sequences/Polypeptides
1.Between genes-e.g. non coding multiple repeats
2.Within genes- Introns
What are introns and exons
Exon Base sequence of a gene coding for amino acid sequences (in a polypeptide)
Intron: Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells
Define Allele
Allele: One of a number of alternative forms of a gene
What is a homologous pair
Chromosomes that are the same size, have the same genes but might have different alleles
What is the role of histones
To tightly coil the DNA to fit chromosomes into the nucleus
What is a nucleosome
The DNA histone complex -basiaclly just hitsone wrapped aorund the DNA
How is the DNA in Mitochondria and Chloroplasts similar to Prokaryotic DNA
DNA is shorter, circular and not histone bound
What is the start codon
-Triplet of bases present at the start of every gene
-Initiates translation
What is the Stop codon
-Triplet of bases present at the end of every gene
-Stops translation by causing the ribosome to detach
Degenerate
There are 20 amino acids
There are 4 bases and therefore three bases are needed to make enough combinations to code for at least 20 amino acids
Can be proven mathematically by (4^n)
Why is the genetic code being degenerate an advantage
This is an advantage as if a point
mutation occurs, even though the
triplet of bases will be different, it may
still code for the same amino acid and
therefore have no effect
Why is the genetic code being universal an advantage
This is an advantage as
if it means genetic
engineering is possible.
E.g. inserting the human
gene for insulin into
bacteria
Why is the genetic code being non overlapping an advantage
If a point mutation occurs it will only affect one codon and therefore one amino acid
What is splicing
The removal of Introns in eukaryotic DNA
