TAILIEUCHUNG - SAT II Biology Episode 1 Part 7

Tham khảo tài liệu 'sat ii biology episode 1 part 7', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | MOLECULAR GENETICS DNA AND EVOLUTION Nucleotides DNA backbone The building blocks of DNA nucleotides are used to make up the repeating units in the strands of DNA that represent the genetic code. A nucleotide consists of a sugar a phosphate and a nitrogen base. Since there are only four bases researchers postulated that the enormous amount of genetic variation on the planet had to be in the sequence of the nucleotides within the DNA molecule. This sequence then controls the synthesis of precise proteins in the sequence of amino acids. On one end of the DNA molecule the 5-carbon sugar has a phosphate attached and is known as the 5 end. On the other end of the sugar is an OH that is identified as the 3 end of the DNA molecule. Bases Four nitrogenous bases make up the bonding sites along the center of the DNA molecule and are bonded to a carbon on the sugar molecule. There are two purines and two pyrimidines. The purine names end in -nine. Peterson s SAT II Success Biology E M mJ CHAPTER 5 Deoxyribose Sugar DNA Nucleotide A. Adenine A purine double-ring base with two bonding sites B. Thymine A pyrimidine single-ring base with two bonding sites C. Cytosine A pyrimidine single-ring base with three bonding sites D. Guanine A purine double-ring base with three bonding sites Ribose A 5-carbon sugar as signified by the -ose ending ribose is considered the central part of the nucleotide as the bases and the phosphate bond to it. Phosphate Bonded to another carbon on the ribose sugar the last phosphate on the molecule is the 5 end. Peterson s SAT II Success Biology E M mj MOLECULAR GENETICS DNA AND EVOLUTION Histones Histones are proteins that help protect the DNA molecule. The DNA molecule is surrounded by eight or nine histones to help it form a protective DNA-histone complex in a tight space in the nucleus. Base-pairing Base-pairing is the pairing of complimentary bases along the DNA strand. The sum of the bonds and the coiling of DNA .

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