Struct a funct. of DNA Flashcards
Describe the Frederick Griffith experiment
-1928
-usage of bacteria: streptococcus pneumoniae
-rough strain (nonvirulent) >mouse lives
-smooth strain (virulent) >
Mose dead
-heat killed smooth strain> mouse lives
-rough strain & heat-killed smooth strain >
mouse dead
How did Avery, McCarty, snd MacLeod find out theGriffith’s transforming principle?
-have to obtain small amounts of highly purified transforming principle
(->through biochemical steps, purified the transforming principle by washing away, separating out, or enzymatically destroying the other cellular components)
->transforming principle might be DNA
How did they find out that it was DNA and not protein?
- test gave negative results for detecting protein; positive for DNA
- The elemental composition of the purified transforming principle closely resembled DNA in its ratio of nitrogen and phosphorous
- enzymes able to degrade DNA eliminated the transforming activity (Protein- and RNA did not=
Describe the Hershey-Chase experiment
- Hershey and Chase studied bacteriophage, or viruses that attack bacteria
- one batch of phage was labeled with ^35S, which is incorporated (verburden) into the protein coat (Hülle) another batch was labeled with ^32P, which is incorporated into the DNA
- 2.bacteria were infected with the phage
- 3.the cultures were blended and centrifuged to separate the phage from bacteria
- 4.Radiactivity was measured in the pellet and liquid (supernatant (außen)) for each experiment
- > ^32P found in pellet (inside bacteria)
- > ^35S found in supernatant (outside of bacteria)
What are genes? What do genes in the sperm and egg cells carry?
- Genes: information containing elements
- they carry the hereditary information
Chromosomes are the carry of? Genes are made of which substance?
- inherited information
- deoxyribonucleic acid (DNA) in the chromosomes is the substance of which genes are made
How long is DNA? DNA is composed of which 4 subunits?
- DNA is a very long, thin, unbranched polymer with a diameter of 2 nm and a length that can extend to 10^8-10^9 nm
- composed of only 4 types of subunits called deoxyribonucleotides: adenine (A), cytosine (C), guanine (G), and thymine (T
How are nucleotides linked together?
-Nucleotides are linked together by covalent phosphor-diester bonds that join the 5’ carbon of one deoxyribose group to the 3’ carbon of the next
Which roles must the DNA fulfill as an energy storage?
- It must be able to encode the genetic information required to specify proteins
- It should be packaged in a compact form that allows the accessibility of that information to be regulated
- It must be compacted into a small volume while maintaining accessibility!
Around what is DNA wrapped?
-145 bp of DNA are wrapped in 1.6 turns tightly around a histone octamer
How many nucleotide pairs of DNA does nucleosome include?
-around 200
In which two forms does the information encoded by DNA occur?
- digital and analogue
- > digital:
- the precise base specifying for example amino acid sequences
- > analogue:
- the structural code, determined not by individual base pairs, but by the additive interactions of successive bas steps (locally more continuous)
- the manifestation of analogue properties is dependent on the length of the DNA sequence
How is the general structure of DNA constructed?
- DNA is a helical polymer composed of two strands. (Watson-Crick model or double helical model)
- All of the bases of the DNA molecule are on the inside of the double helix, the sugar phosphates are on the outside
How does the base pairing look of a DNA sequence look like?
- Specific base-pairing between a large purine base (A or G) on one chain and a smaller pyrimidine base (T or C) on the other chain
- Complementary base pairs form between A and T and between G and C. Quantitatively G=C and A=T
Describe DNA replication in general
- Biological information in the gene is copied and transmitted from each cell to all of its progeny
- Strand A can serve as a template for making a new strand A’, and vice versa
- Strand A separates from strand A’ and each serves as a template for the production of a new complimentary strand
- DNA carries information by means of sequence of its nucleotides
Why do organisms differ?
- their DNA molecules carry different nucleotide sequences and different biological messages
Describe DNA replication more specific
- Replication of the DNA helix begins with the separation of its two complementary DNA strands
- Each strand acts as a template for the formation of a new DNA molecule
- New DNA forms by the sequential addition of deoxyribonucleoside triphosphates
- Eventually, genetic information is duplicated in its entirety
- > DNA replication is said to be semiconservative
How many errors occur in DNA replication?
-Several proofreading mechanisms are used (<1 mistake in 10^9 nucleotides added)
What are possible outcomes of a DNA replication error ?
- genetic mutation:
- Results can be great, for example a crucial protein can be inactivated
- a mutation may be silent and not affect the function of a protein
- Very rarely, it can create a gene with an improved or novel useful function
What determines the amino acid sequence of a protein?
-The nucleotide sequence of a gene
What is gene expression?
-translation of a linear sequence of nucleotides into a co-linear sequence of amino acids in proteins
How does gene expression happen?
- A limited segment of DNA is first copied into a complementary strand of RNA. This primary RNA transcript is spliced to remove intron sequences (non-coding regions), producing an mRNA molecule
- Finally, the mRNA is translated into protein in a complex set of reactions that occur on a ribosome
- The amino acids used for protein synthesis are first attached to a family of tRNA molecules, each of which recognizes three nucleotides in the mRNA (codons)
- The sequence of nucleotides in the mRNA is then read from one end to the other in sets of three
As what do other RNA molecules function?
-as enzymelike catalysts
>One of these catalysts is the large rRNA of the ribosome, which catalyzes the formation of peptide bonds during protein synthesis
Why is DNA, and not RNA, now the dominant biological information store?
- DNA can adopt (at least) two forms of right handed double-helical structures, A-DNA and B-DNA
- RNA can only form an A-type double helix
Advantages of conferring B-DNA over not being able to confer
- advantages for both information accessibility and for packaging
- > An A-type double helix is stiffer than B-type double helix
- Distortion (Verzerrung) of A-DNA to a particular bent configuration is energetically less favourable than for the corresponding distortion in B-DNA
Differences of major and minor groove
- The major groove provides more sequence information than the minor groove
- Access to the DNA major groove is more facile than to the minor groove
- Note the difference in groove width (Breite) and the relative displacements of the base pairs from the central axis (A-DNA)
Another advantage to being able to adopt the B-form
-facilitates direct access to DNA sequence information
Name other alternative DNA structures
- DNA bubble
- Z-DNA
- slipped loop
- cruciform
- H-DNA
- G-quadruplex/i-motif
