DNA,genes And Chromosomes Flashcards
Chromosomes in Prokaryotes
They lack a nucleus or membrane bound organelles
Chromosomes in Eukaryotes
It has a membrane bound nucleause with linear chromosomes
Locus
Fixed position of a gene on a DNA molecule
What holds tightly coiled DNA in place?
Histones
What do Histones and DNA form?
The proteins help to support DNA and fix it in position
Forms a DNA-Histone complex which then coils more
What do chromosomes consist of?
2 chromatids and one centromere
Describe DNA molecules in mitochondria in chloroplasts
Shorter than in nucleus
Circular not linear
Not associated with Histones proteins
Similar to prokaryotic DNA
Describe DNA in prokaryotes
Circular not linear
Can be called a bacterial chromosome
Shorter
Not associated with Histones
It fits into the cell by coiling tightly-supercooling
What is a gene
A base sequence of DNA that codes for amino acid sequence of a polypeptide or a functional RNA
What is a functional RNA?
Descríbeles RNA molecules (other than mRNA) which perform specific functions during protein synthesis
E.g. tRNA and rRNA-forms part of chromosome
Alleles
More than one form of a gene
The order of bases is slightly different in each so they code for different versions of the same polypeptide
Homologous chromosomes
One of each pair of chromosomes is provided by the mother, and the other the father
diploid number of chromosomes in humans
46
Number of chromosomes in sperm and egg cells
Haploid-23
What is the triplet code?
3 DNA bases code for one amino acid
Why is the genetic code known as degenerate?
Because most amino acids have more than one triple code
Most have between 2 and 6
what directions are the triplet codes read in?
Always read in one direction along the DNA strand
Stop codes
Three triplet codes that dont code for any amino acid
They mark the end of the polypeptide chain
Give 2 other features of the genetic code other than it is degenerate
Non-overlapping- each base in the sequence is only read once
Universal- the same in all organisms
What is a codon?
The 3 complementary bases (to the triplet code on DNA) on mRNA
Some genes dont code for polypeptides. What do they code for?
Functional RNA e.g. rRNA tRNA
Introns
Sections of genes that dont code for amino acids
They are removed in protein synthesis so they dont affect the amino acid sequence
Prokaryotic DNA doesnt have them
Exons
The parts of the gene that do code for amino acids
Genetic code
Is carried on dna
How will the protein structure be affected if there is changes to the base sequence on the DNA molecule?
The triplet code on the DNA changes
Leads to a change in the sequence of amino acids/primary structure of protein
Bonds form in different places, primary structure folds differently
Changes the tertiary structure of a protein/shape of the active site of enzyme
