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DNA and DNA Replication

Terms in this set (26)

Explain why researches originally thought protein was the genetic material
Protein was originally thought to be the genetic material because of its complexity; protein is made up 20 different amino acids while DNA only consists of four bases.
This was logical as the complexity would account for diversity in organisms.
Describe the structure of DNA. Explain the base-pairing rule and describe its significance.
a. Double-helix made up of small molecules called nucleotides; Each nucleotide comprises a 5-carbon sugar, a nitrogenous base and a phosphate group; joined together by 'twisted ladder'
b. A=T; G=C
c. The main significance of base pairing is the amino acid sequence
Describe the process of DNA replication, including the role of the origins of replication and replication forks.
a. Replication begins at specific sites, origins, where two parental strands separate to form replication bubbles
b. Bubbles expand laterally as DNA replication proceeds in both direction; end of bubbles are called replication forks (Y-shaped region)
c. Replication bubbles fuse, and synthesis of daughter strands is completed
Explain the role of DNA polymerases in replication.
New DNA elongation at replication form is catalyzed by DNA polymerase; as nucleotides align with complementary bases along template strand, they are added by polymerase to growing end of new DNA strand
Explain what energy source drives the polymerization of DNA.
Nucleoside triphosphates; as each monomer joins growing end of DNA strand, it loses 2 phosphate groups; subsequent hydrolysis of pyrophosphate to two molecules of inorganic phosphate is exergonic reaction that drives polymerization reaction
Define antiparallel and explain why continuous synthesis of both DNA strands is not possible.
a. DNA strands' sugar-phosphate backbones run in opposite directions
b. Continuous synthesis of both DNA strands is not possible because the two strands run in opposite direction, and DNA polymerases add nucleotides only to free 3' end not 5'
Leading strand
is synthesized in the same direction as the movement of the replication fork;
is synthesized continuously
Lagging strand
synthesized in the opposite direction of leading strand;
lagging strand is synthesized in short fragments that are ultimately stitched together (Okazaki fragments)
Explain how the lagging strand is synthesized even though DNA polymerase can add nucleotides only to the 3' end.
As replication bubble opens, polymerase molecule work its way away from replication fork and synthesize a short segment of DNA.
DNA ligase
enzyme that joins with sugar phosphate backbones of Okazaki fragments to create DNA strand
Primer
an already existing RNA chain bound to template DNA to which DNA nucleotides are added during DNA synthesis
Primase
an enzyme that joins RNA nucleotides to make the primer
HElicase
enzyme that untwists double helix at replication fork
Topoisomerase
are enzymes that regulate the overwinding or underwinding of DNA
Single strand binding proteins
during DNA replication, molecules that line up along the unpaired DNA strands, holding them apart while the DNA strands serve as templates for the synthesis of complimentary strands of DNA
Explain the roles of DNA polymerase, mismatch repair enzymes, and nuclease in DNA proofreading and repair.
a. DNA polymerase proofreads each nucleotide against its template as soon as it is added to growing strand
b. In mismatch repair, cells use special enzymes to fix incorrectly paired nucleotides
c. Nuclease - DNA cutting enzyme, cuts out damaged segment
Explain how RNA differs from DNA
RNA's sugar is ribose
DNA's sugar is deoxyribose
How does information flows from gene to protein?
Nucleic acids and proteins contain information written in two different chemical languages. To get from DNA, written in one language, to protein, written in another, requires two major stages, transcription and translation
Transcription
synthesis of RNA under the direction of DNA
Translation
actual synthesis of polypeptide, which occurs under the direction of mRNA
Compare where transcription and translation occur in prokaryotes and in eukaryotes
a. In prokaryotic cell, mRNA produced by transcription is immediately translated without additional processing
b. In eukaryotic cell, the nucleus provides a separate compartment for transcription. The original RNA transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA
Codon
mRNA base triplets
Explain the evolutionary significance of nearly universal genetic code.
A language shared by all living things must have been operating very early in the history of life - early enough to be present in the common ancestors of all modern organisms. A shared genetic vocabulary is a reminder of the kinship that bonds all life on Earth.
Describe the structure and functions of tRNA.
a. tRNA looks kind of like a puzzle piece shaped like a t, fittingly, and it reads the instructions for assembling unique proteins so that the ribosomes know how to make them.
b. Interpreter of codons along mRNA molecule
Explain how tRNA is joined to the appropriate amino acid.
The key to translating a genetic message into a specific amino acid sequence is that each type of tRNA molecule links a particular mRNA codon with a particular amino acid.
Describe the structure and functions of ribosomes.
a. Made of two subunits
b. Its job is to translate mRNA and make proteins using the information in the mRNA
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