Chapter 8: DNA, RNA and the Flow of Genetic Information

Exam 2

central dogma

DNA to RNA (transcription) to protein (translation)

DNA

A nucleic acid constructed of four different deoxyribonucleotides; contains the genome and exists as a double-stranded helix in all higher organisms

RNA

A long unbranched polymer consisting of ribonucleotides joined by 3′→5′ phosphodiester linkages that plays many roles in the cell, including that of catalyst

nucleotide

A nitrogenous purine or pyrimidine base linked to a sugar, which is in turn linked to one or more phosphoryl groups

nucleoside

nitrogenous base + sugar, linked through beta-glycosidic linkage

deoxyribose

A five-carbon monosaccharide (C5H10O4) that constitutes the carbohydrate moiety of a deoxynucleotide

ribose

A five-carbon monosaccharide (C5H10O5) that constitutes the carbohydrate moiety of ATP, other ribonucleosides and ribonucleotides, and cofactors such as NAD+ and coenzyme A

purine

A nitrogenous base that includes a pyrimidine ring fused with a five-membered imidazole ring; the purine derivatives adenine and guanine

pyrimidine

A nitrogenous base that is a six-membered heterocyclic ring containing two nitrogen atoms and four carbon atoms; the pyrimidine derivatives cytosine, uracil, and thymine

DNA structure

• right-hand screw

• antiparallel 5’ to 3’

• CG and AT

• 10 bases per helix turn

• phosphodiester linkages between sugars

• sugar phosphate backbone

B form of DNA

• Watson-Crick model

• bases are separated by 3.4 A

• helix width is 20 A

• helical structure repeats 34 A = 10 bases per helix turn

• major/minor groove

A form of DNA

• right-handed

• wider/shorter

• base pairs tilted relative to helical axis

• found in dehydrated DNA, double stranded RNA, DNA:RNA hybrids

Z form of DNA

• left-handed

• backbone zig-zags

• narrowest form of DNA

• syn and anti base + sugar orientation

stem-loop

A nucleic acid structure, commonly seen in RNA, created when two complementary sequences within a single strand come together to form a double-helical structure, which constitutes the stem

semiconservative replication

The type of replication observed in the duplication of DNA, in which one of the strands of each daughter molecule is newly synthesized, whereas the other is unchanged from the parental DNA double helix

components for DNA replication

• all 4 activated nucleotides (dATP, dGTP, dCTP, dTTP)

• Mg2+ ion

• template DNA

• primer

DNA replication process

• DNA polymerase binds to primer on template strand

• chain-elongation begins in 5’ to 3’ direction

melting temperature

For a DNA double helix, the temperature at which half of the helical structure is lost

template strand

In DNA or RNA, a sequence that directs the production of a complementary sequence

primer

In the elongation of polymers, the initial segment of the polymer that is to be extended

retrovirus

A class of RNA viruses in which genetic information flows from RNA to DNA following the insertion of a copy of the viral RNA genome into the host’s DNA

messenger RNA (mRNA)

A class of RNA molecules that serve as templates for the synthesis of proteins

transfer RNA (tRNA)

The adaptor molecule in protein synthesis; contains an amino-acid-recognition site as well as a template-recognition site, or anticodon

ribosomal RNA (rRNA)

The RNA components of ribosomes, catalytic function for protein synthesis

transcription

DNA-directed synthesis of RNA catalyzed by RNA polymerase

RNA polymerases require

• template strand

• activated precursors (ATP, GTP, UTP, CTP)

• Metal ion (Mg2+)

transcription process

• 5’ to 3’ direction

• elongation

• driven forward by hydrolysis of pyrophosphate

promotor site

A specific sequence of DNA, usually just upstream of a gene, that specifies the start site and extent of transcription of the associated gene

codon

A nucleotide triplet in mRNA that encodes a particular amino acid

anticodon

A nucleotide triplet in tRNA that binds to a specific codon within an mRNA molecule during transcription

aminoacyl-tRNA

A tRNA molecule that has been covalently linked to the amino acid corresponding to its anticodon sequence

genetic code

The relationship between nucleic acid sequence information and protein sequence information

stop codon

In most organisms, one of three nucleotide triplets in mRNA that designate the termination of transcription

ribosome

A large ribonucleoprotein assembly that catalyzes the formation of peptide bonds

intron

Region of the primary transcript that is removed in the mature mRNA

exon

Region of pre-mRNA that is retained in mature mRNA

splicing

The removal of introns and the ligation of exons from precursors of RNA to form mature RNA

alternative splicing

The generation of unique but related mRNA molecules by the differential splicing of the pre-mRNA transcript