University:
Kentucky State University
Course:
CHE 315 | Biochemistry
Academic year:

2024
Views:

231

Pages:

25
Author:

Tarime9wn

Nucleic Acids and Protein Synthesis 1 Terms • DNA: deoxyribonucleic acid • RNA: ribonucleic acid • Chromosomes: the WHOLE long strand of DNA (in eukaryotes, because the DNA is complexed with proteins, the DNA is called a chromatin) 2 Gene 2 Gene 1 4 Chromosome vs. chromatin • Chromatin is not condensed (uncoiled) and cannot be distinguished from each other before cell division. • Chromosomes: condensed (coiled) DNA molecules that can be distinguished from other chromosomes at cell division. 5 6 DNA and RNA are polymers • DNA and RNA are known as nucleic acids • They are linear polymers composed of monomers called nucleotides 7 Chemical composition and bonds • All nucleotides have a common structure: – a phosphate group linked by a phosphoester bond to a pentose – The pentose is linked to a nitrogenous base via a glycosidic bond 8 Glycosidic bond 9 DNA vs. RNA • In RNA, the pentose is a ribose • In DNA, it is a deoxyribose 10 Nitrogenous bases • DNA and RNA each consists of only four different nucleotides of two classes: purines and pyrimidines • Purines are adenine and guanine • Pyrimidines are cytosine, thymine, and uracil • The bases adenine, guanine, and cytosine are found in both DNA and RNA • Thymine is found only in DNA • Uracil is found only in RNA • The bases are often abbreviated A, G, C, T, and U, respectively 11 The bases 12 How are bases connected to ribose? • In nucleotides, the 1 carbon atom of the sugar (ribose or deoxyribose) is attached to the nitrogen at – position 9 of a purine (N9) or – position 1 of a pyrimidine (N1) 13 Nucleotides are acidic • Due to the presence of phosphate, which dissociates at the physiological pH inside cells, freeing hydrogen ions and leaving the phosphate negatively charged 14 Nucleotides vs. Nucleosides • Nucleosides are combinations of a base and a sugar without a phosphate • Nucleotides are nucleosides that have one, two, or three phosphate groups esterified at the 5’ hydroxyl • Nucleoside monophosphates have a single esterified phosphate – diphosphates contain a two phosphate group – triphosphates have three phosphates 15 Nucleotides vs. Nucleosides Nucleotides 16 17 Nucleic acid polymer • When nucleotides polymerize to form nucleic acids, the hydroxyl group attached to the 3’ carbon of a sugar of one nucleotide forms a bond to the phosphate of another nucleotide • A single nucleic acid strand is a phosphate-pentose polymer (a polyester) with purine and pyrimidine bases as side groups • The links between the nucleotides are called phosphodiester bonds 18 Directionality • A nucleic acid strand has an end-to-end chemical orientation: • The 5’ end has a free hydroxyl or phosphate group on the 5’ carbon of its terminal sugar • The 3’ end has a free hydroxyl group on the 3’ carbon of its terminal sugar • This directionality has made polynucleotide sequences written and read in the 5'®3' direction (from left to right) • Example: the sequence AUG is assumed to be (5')AUG(3') 19 DNA structure • DNA consists of two associated polynucleotide strands that wind together through space to form a structure often described as a double helix. 20 DNA structure • The sugar-phosphate groups are on the outside of the double helix, and the bases project into the interior. • The sugar-phosphate groups are termed backbone. • The orientation of the two strands is antiparallel. 21 RNA structure • Note: RNA is usually single-stranded and does not have a specific structure 22 Base pairing • In DNA, the larger purine (A or G) must pair with a smaller pyrimidine (C or T) • A almost always hydrogen bonds with T and G with C, forming A·T and G·C base pairs • A is paired with T through two hydrogen bonds; G is paired with C through three hydrogen bonds 23 Chargaff's rules • In addition, Erwin Chargaff established certain rules about the amounts of each component of DNA: – – – – Pyrimidines (T + C) always equals purines (A + G). T always equals A. C always equals G. A + T is not necessarily equal to G + C. 24 Genetic heredity • It is the transfer of genetic material (DNA) from parents to offspring. • When a sperm fertilizes an egg, it combines a full set of DNA (one set of DNA molecule comes from father and one set DNA molecule from mother). • Cells divides and every time a cell divides, DNA must be copied. • When a “mother” cell divides, the information is passed along to the daughter cells, which ultimately pass this genetic information to their daughter cells. • Within cells, the genetic information is encoded in the DNA and it directs the synthesis of proteins, a process known as the expression of DNA. 25 Genetic processes • The genetic information occur as the result of three fundamental processes: • Replication is the process by which an identical copy of DNA is made when a cell divides. • Transcription is the process by which the genetic messages contained in DNA are read and copied into RNA, which carry the instructions stored in DNA out of the nucleus to the sites of protein synthesis. • Translation is the process by which the genetic messages carried by RNA are used to build proteins. 26

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