Lab 2 - Human genome Flashcards
DNA molecule basic components
The pentose sugar, deoxyribose, a phosphate group and four types of nitrogenous bases
Pyrimidines
Cytosine and thymine
Single carbon-nitrogen rings
Purines
Adenine and guanine
Double-carbon nitrogen rings
How many hydrogen bonds between cytosine-guanine pairs?
Three
How many hydrogen bonds between adenine-thymine pairs?
Two
DNA coiling
First DNA is wound around a histone proteins core to form nucleosome –> nucleosome form a helical solenoid, each turn including six nucleosomes –> solenoid are organized into chromatin loops
Each nucleotide subunit consist of
One deoxyribose, one phosphate group and one base
Gene definition
A functional unit in the genome that contains the genetic information for one or more gene products
Protein-coding gene
Three components: the coding sequence, regulatory sequence, and seemingly useless sequences
Within the genomic DNA, a gene is defined by
The direction of transcription in the 5’ to 3’ direction
Sense strand
The DNA strand which corresponds to the RNA sequence
Antisense strand
Complement of the sense strand (which serve as a template for RNA biosynthesis)
UTR - Untranslated regions
The sequence before the start codon and after the stop codon
AAUAAA
Polyadenylation signal where transcription terminates
Introns
Noncoding sequence in a gene that are positioned between coding sequences (exons) and removed by splicing from the pre-mRNA transcript
Exons
Coding sequences in the pre-mRNA that are separated by noncoding introns
Tandem repeats
occur in DNA when a pattern of one or more nucleotides is repeated and the repetitions are directly adjacent to each other
Satellite DNA
Repeats are clustered together in certain chromosome locations, where they occur as tandem repeats
Dispersed repetitive DNA
tend to be scattered singly throughout the genome; they do not occur in tandem
Satellite DNA can easily be separated by
Centrifugation in a cesium chloride density gradient
Alpha satellite DNA:
Tandem repeats of 171-bp sequence. Found near the centromeres of chromosomes. Several million base pairs
Minisatelites
Block of tandem repeats (14 to 500-bp), whose total length is much smaller, usually a few thousand base pairs
Microsatellites
Smaller, repeat units are 1 to 13-bp, and the total length of the array is usually less than a few hundred base pairs
Why are minisatellites and microsatellites of special interest in human genetics?
Because they vary in length among individuals, making them highly useful for gene mapping
Transposons
“Jumping genes”, mobile DNA elements. DNA sequences are able to leave a chromosome and to reenter the genome at nonhomologous points of the DNA
Retrotransposons
The DNA sequence is multiplied through reverse transcription of mRNA into cDNA, which is integrated into a different location
Long terminal repeat (LTR)
5-10 kb. Central protein-encoding region is flanked by LTR or non LTR
Long interspersed elements (LINEs)
Up to 7 kb
Short interspersed elements (SINEs)
Up to 300 bp, incl. Alu
Alu
Can mediate an asymmetric recombination and cause genomic deletions and duplications
DNA molecules of mitochondria
Base pairs arranged on a double stranded circular molecule. Encodes 2 rRNAs and 22 tRNAs. Contain no introns. Males do not transmit mtDNA
Mutation rate of mtDNA
10 times higher than nuclear DNA. (lack of RNA repair mechanism + damage from free oxygen radicals
Threshold effect
Whether a heteropasmic mitochondrial is expressed phenotypically depends on the proportion of the cell’s normal mtDNA to mutated mtDNA
Organs that are most affected by mitochondrial diseases
CNS, heart, kidney
Symptoms of mitochondrial diseases
Encephalopathy Myopathy Cardiomyopathy External ophthalmoplegia Retinal degenaration Renal dysfunction.
When does MERRF syndrom (myoclonic epilepsy with Ragged Red Fibers) typically presents symptoms?
Childhood
What does myoclonus progress into?
Generilized epilepsy, ataxia, weakness, finally dementia. Short stature, hearing loss, optic atrophy, cardiomyopathy
Leber herditary optic neuropathy
Affect optic nerve, acute painless loss of vision, progress to severe optic atrophy, males>females. Many carriers remain asymptomatic
Kearns-Sayre syndrome
CPEO (chronic progressive external ophthalmoplegia), retinopathy, ptosis, deafness, cardiac arrhythmias, ataxia
