Struct a funct. of DNA

Question 1

Describe the Frederick Griffith experiment

Answer 1

-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

Question 2

How did Avery, McCarty, snd MacLeod find out theGriffith’s transforming principle?

Answer 2

-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

Question 3

How did they find out that it was DNA and not protein?

Answer 3

• 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=

Question 4

Describe the Hershey-Chase experiment

Answer 4

• Hershey and Chase studied bacteriophage, or viruses that attack bacteria
• 1. 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)

Question 5

What are genes? What do genes in the sperm and egg cells carry?

Answer 5

• Genes: information containing elements

- they carry the hereditary information

Question 6

Chromosomes are the carry of? Genes are made of which substance?

Answer 6

• inherited information

- deoxyribonucleic acid (DNA) in the chromosomes is the substance of which genes are made

Question 7

How long is DNA? DNA is composed of which 4 subunits?

Answer 7

• 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

Question 8

How are nucleotides linked together?

Answer 8

-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

Question 9

Which roles must the DNA fulfill as an energy storage?

Answer 9

• 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!

Question 10

Around what is DNA wrapped?

Answer 10

-145 bp of DNA are wrapped in 1.6 turns tightly around a histone octamer

Question 11

How many nucleotide pairs of DNA does nucleosome include?

Answer 11

-around 200

Question 12

In which two forms does the information encoded by DNA occur?

Answer 12

• 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

Question 13

How is the general structure of DNA constructed?

Answer 13

• 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

Question 14

How does the base pairing look of a DNA sequence look like?

Answer 14

• 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

Question 15

Describe DNA replication in general

Answer 15

• 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

Question 16

Why do organisms differ?

Answer 16

• their DNA molecules carry different nucleotide sequences and different biological messages

Question 17

Describe DNA replication more specific

Answer 17

• 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

Question 18

How many errors occur in DNA replication?

Answer 18

-Several proofreading mechanisms are used (<1 mistake in 10^9 nucleotides added)

Question 19

What are possible outcomes of a DNA replication error ?

Answer 19

• 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

Question 20

What determines the amino acid sequence of a protein?

Answer 20

-The nucleotide sequence of a gene

Question 21

What is gene expression?

Answer 21

-translation of a linear sequence of nucleotides into a co-linear sequence of amino acids in proteins

Question 22

How does gene expression happen?

Answer 22

• 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

Question 23

As what do other RNA molecules function?

Answer 23

-as enzymelike catalysts
>One of these catalysts is the large rRNA of the ribosome, which catalyzes the formation of peptide bonds during protein synthesis

Question 24

Why is DNA, and not RNA, now the dominant biological information store?

Answer 24

• 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

Question 25

Advantages of conferring B-DNA over not being able to confer

Answer 25

• 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

Question 26

Differences of major and minor groove

Answer 26

• 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)

Question 27

Another advantage to being able to adopt the B-form

Answer 27

-facilitates direct access to DNA sequence information

Question 28

Name other alternative DNA structures

Answer 28

• DNA bubble
• Z-DNA
• slipped loop
• cruciform
• H-DNA
• G-quadruplex/i-motif