Chapter 17

Transcription

In the nucleus, genetic information for the synthesis of a protein is copied from a gene in DNA to make mRNA.

Transfer RNA (tRNA)

Interrupts the genetic information in the mRNA and brings specific amino acids to the ribosomes for protein synthesis.

DNA Base Pairs

Number of Purine Bases = Number of Pyrimidine Bases A = T G = C

Activation of tRNA

Occurs when aminoacyl-tRNA synthetase forms an ester bond between carboxylate group of its amino acid and hydroxyl group on the acceptor stem.

Translation

tRNA molecules convert the information in the mRNA into amino acids, which are placed into proper sequence to synthesize a protein.

Chain Termination

-All the amino acids are linked. -The ribosome reaches a "stop" codon. -There is no tRNA with an anticodon for the "stop" codon. -The polypeptide chain detaches from the ribosome. -The initial amino acid is usually removed from the beginning of the protein chain.

Nucleotides

-Are nucleoslides in which a phosphate group bonds to the -OH group on carbon 5 of ribose or deoxyribose to produce a phosphate ester. -Are not formed when other hydroxyl groups on ribose form phosphate esters.

Nucleic Acids

-Are polymers in which the 3'-hydroxyl group of the sugar in one nucleotide bonds to the phosphate group on the 5'-carbon atom in the sugar of the next nucleotide. -Have one terminal end with an unreacted or free sugar with a 5'-phosphate. -Have a sugar on the other end with a free 3'-hydroxyl group.

Nucleoslide

-Combination of a sugar and base. -Is produced when the nitrogen atom in a pyrimidine or a purine base forms an N-glycosidic bond to carbon 1 of a sugar. -Is named by changing the ending to "osine" for purines and "idine" for pyrimidines.

Components of Nucleic Acid

-General structure of a nucleotide includes a nitrogen containing base, a sugar, and a phosphate group. -In DNA, the purine bases are adenine, guanine, cytosine and thymine. -RNA contains the same bases except thymine is replaced by uracil.

DNA Double Helix

-Has two strands of nucleotides that wind together. -Is held in place by two hydrogen bonds that form between bases pairs AT. -Is held in place by three hydrogen bonds that form the base pairs between CG.

Bases

-Nitrogen containing bases are derivatives of pyrimidine or purine. -In DNA, the purine bases with double rings are adenine (A) and guanine (G). -The pyrimidine bases with single rings are cytosine (C) and thymine (T). -RNA has the same bases except thymine is replaced by uracil (U).

Initiation and Chain Elongation

-The first codon in mRNA is a start codon, AUG, which forms hydrogen bonds. -Another tRNA hydrogen bonds to the next codon, placing a second amino acid adjacent to the first. -A peptide bond forms between the C-terminal and N-terminal of the second amino acid.

DNA Replication

-The strands in the original DNA molecule separate to allow the synthesis of complementary DNA strands. -An enzyme called helicase catalyzes the unwinding of a part of the double helix by breaking the hydrogen bonds. -The resulting single strand acts as templates for the synthesis of new complementary strands of DNA. -As complementary base pairs come together, DNA polymerase catalyzes the formation of the phosphodiester bonds between nucleotides. -The entire double helix of parent DNA is copied. Process produces two new identical DNA strands.

Anticodon

A series of three bases that complements three bases of mRNA.

Messenger RNA (mRNA)

Carries genetic information from DNA in the nucleus to the ribosomes in the cytoplasm.

Complementary Base Pairs

DNA contains complementary base pairs, equal amounts of A and T and equal amounts of C and G bases in which: -Adenine is linked only to thymine by two hydrogen bonds. -Guanine is linked only to cytosine by three hydrogen bonds.

Phosphodiester Bond

The link between sugars in adjacent nucleotides.

Ribosomal RNA (rRNA)

The most abundant type of RNA, is combined with proteins to form ribosomes.