DNA/RNA and DNA Replication Flashcards
Francis Crick, a graduate student, and an American postdoctoral fellow James Watson joined forces in late 1951 at the Cavendish Laboratory at the University of Cambridge and began working together on the structure of DNA.
•They used the data from several groups to build their model of DNA: (2)
–Observations of Erwin Chargaff on base composition of DNA
–X-ray diffraction studies of Rosalind Franklin (and Maurice Wilkins)
Watson’s and Crick’s model of DNA was based on X-ray — — of Rosalind Franklin (at King’s College)
diffraction data
Watson’s and Crick’s Model Provides and explanation for Chargaff’s Rule
of A=T and G=C
In Prokaryotic organisms the DNA is organized in a linear or contiguous fashion and transcription of the DNA into RNA results in a RNA copy that is ready for use as a
template for protein synthesis (translation)
In Prokaryotic organisms the RNA transcript can be translated into a protein during the transcription process as there is no
nucleus
In Eukaryotic organisms the DNA is broken up into regions or blocks of sequence that will give rise to the
protein sequence (coding regions or exons)
These exons are separated by (2)
regions that do not code for protein (introns) and regions at the 5’ and 3’ ends that do not encode protein called untranslated regions (UTRs)
In Eukaryotic organisms one strand of the DNA is first copied in a — fashion and then the introns are removed by a process called —
linear
splicing
Subsequent modifications take place that give rise to the mature mRNA, which is transported out of the nucleus for use as the
temple for protein synthesis (translation)
In Eukaryotic organisms primary transcripts are often spliced in multiple combinations of exons known as
alternative splicing
alternative splicing gives rise to a family of possible proteins that can have slightly different (3)
functions, regulation and/or tissue specificity (i.e. different splice variants are found in different tissues)
Linear DNA must be Condensed in order to
fit into a Cell or Nucleus
in prokaryotes, DNA is condensed by a set of — and proteins in
polyamines
back and forth loops
in eukaryotes, DNA is first condensed into
nucleosomes
each nucleosome involves (2)
~200 bp of DNA and a set of core histone proteins
Nucleosomes look like a “beads on a string” and are usually packaged together to give
chromatin fiber structure
Chromatin exists in what two forms?
euchromatin and heterochromatin
Euchromatin (2)
a more relaxed structure and transcriptionally active
Heterochromatin (2)
more highly condensed and generally not transcriptionally active
Chromatin can be further condensed into (3 steps)
solenoids then supersolenoids ultimately into chromosomes by function specific sets of proteins
bacterial vs eukaryotic chromosomes
bacteria have a single major heritable unit or chromosome
DNA in eukaryotic cells is packaged into several chromosomes
Bacteria can also have separate smaller DNA entities called
plasmids
eukaryotes also have DNA genomes in their
mitochondria
plants have a DNA genome in their
chloroplasts
how many protein coding genes?
~20,000-25,000
The average gene is about — bp long, contains about — exons and a coding sequence of about — bp
27,000
9
1340
The full set of proteins or proteome is more complex, it is estimated that the average gene gives (2)
8 isoforms, splice variants, etc.
Human Genome: ~ – billion bp
3.2
Mutation that can cause disease: – bp
1
Differences between siblings: ~ – million bp
1-2
Difference between unrelated humans: ~ – million bp
6
Humans vs. Chimps: ~ – million bp different
50
Humans vs. Mice: ~ – million bp different
100
— orientation of the strands
Antiparallel
Strands are —
complementary
Each strand can act as a — for the synthesis of a new strand
template
