2.7 Flashcards
what happens when a cell divides
two daughter cells that are identical copies of the parental cells are formed
what is replication
the formation of a new DNA molecule and occurs during the S phase of the cell cycle
what happens to the chromosome number and genes during DNA replication
the chromosomes and genes stay the same, only the DNA molecules change as they double
what are the steps of replication
- unwind the coils to make the strand accessible to enzymes.
- the enzyme helices then unwinds the double helix and separates the two DNA strands by breaking the hydrogen bonds between the bases
- DNA polymerase can then stat making new strands of DNA using the two old parent strands as templates.
what direction does replication alway take place in
5’ to 3’ prime
meaning as one is antiparallel, It moves in the reverse direction on the other strand
what is DNA replication like
it is semi conservative because each daughter molecule formed contains one original strand from the old molecule and one newly synthesized strand
Name the enzyme that separates the two strands of the DNA double helix during replication.
helicase
what did Meselson and Stahl find
that DNA replicated semi conservatively
what are the three possible ways DNA could be replicated
Dispersive - sections
conservative - two separate strands
Semi conservative - mix of each strand
Steps of meselson ad stahl experiment
they cultured E.coli in the presence of a heavy isotope N15. DNA contains nitrogen in its nitrogenous bases so the radioactive would end up in the DNA of the bacteria. the result was that all bacteria had 15N in its bases
they then transferred the bacterial culture into a fish medium where the nitrogen was replaced by 14N a lighter isotope and the bacteria were allowed to grow for several generations.
DNA samples were then extracted from successive bacterial generations sand subjected so a cesium chloride equilibrium density gradient centrifugation .
this technique allowed the DNA to move to different positions in the centrifuge tube based on its density. DNA containing one or two strands with 15N was heavier and showed lower bands than those containing two strands with 14N.
What did meselson and stahl find
after one generation one division of the bacteria, the resulting DNA strand consisted of a double helix where one strand was made up of 15 N, and the other contained 14N. the band obtained was in between those for DNA with both strands contains 15N or 14N only.
what did the results of meselson and stahl demonstrate
DNA replication had to proceed in a semi conservative way and should involvecomplementary base pairing to ensure the fidelity fo the daughter molecules, results of the successive generations of bacteria further confirmed this theory
Which method was used in Meselson and Stahl’s experiment to prove their theory about the semi-conservative nature of the DNA replication?
use of isotopes
What takes place to the DNA in transcription
the coding information is copied/transcribed into a special molecule called messenger RNA (mRNA). the DNA functions as a template and the single stranded mRNA molecule that is made follows the complementary base paring rules of DNA,
What is the corresponding base sequence of the DNA strand of GCU CCU GAG UUG
CGA GGA CTC AAC
what is the role of RNA polymerase
responsible for separating the DNA strands of the double helix as well as for joining the ribonucloetides together by phosphodiester bonds to form an mRNA strand
what is the DNA strand that is not transcribed called
sense strand
has the same sequence as the base of the mRNA except fo thymine
what is the transcribed strand known as
the antisense strand
Antisense strand - TGA CCG TTA
give sense and mNA strand
DNA sense sequence: ACT GGC AAT
mRNA strand: ACU GGC AAU
what is the antisense strand also called
the template strand
what enzyme is responsible for uncoiling and separating the DNA strands during transcription
RNA polymerase
what step comes after transcription
translation
what is translation
the synthesis of polypeptides on ribosomes according to the genetic code