DNA
DeoxyriboNucleic Acid
DNA
DeoxyriboNucleic Acid
Characteristics of DNA
1. a polymer (composed of repeating subunits)
2. made of two long strands, chains of nucleotides
a. five-carbon sugar- deoxyriboseb. phosphate group
c. nitrogen base
1. purines
a. adenineb. guanine
2. pyrimidines
a. thymineb. cytosine
twists around a central axis to form double helix: looks like a twisted ladder. discovered by Watson and Crick.
nitrogen bases
adenine <-> thymine
cytosine <-> guanine
keeps rungs of ladder even
makes each strand an exact complement of the other
Nucleotides: the building blocks of DNA
duplication of DNA: an enzyme, helicase, "unzips" the two strands. the unpaired bases in each strand react with complementary bases of nucleotides floating freely in nucleus. another enzyme, polymerase, connects the sugar and phosphate groups.
RESULTS: two new DNA molecules, identical to the first. each consists of one old strand and one new strand.
Replication occurs at many different places along the molecule simultaneously. it does not start at one end and work its way down.
Enzymes are used to recognize and "proofread" DNA to make sure it is copied correctly and to repair DNA to prevent mutations.
Proteins are composed of polymers called polypeptides. The polypeptides are made of chains of amino acids. (There are 20 different amino acids). The amino acids must be arranged in a particular sequence if the protein is to function properly.
*****muscles and skin are mostly proteins
*****enzymes, proteins that serve as catalysts, are essential to cells in carrying out life functions
a. enzymes speed up reactions by lowering activation energy.
b. enzymes end in -ase
(RNA)
RNA functions primarily in directing protein synthesis.
RNA differs from DNA in three ways:
a. only one strand of nucleotidesb. its sugar is ribose instead of deoxyribose
c. it has the nitrogen base uracil instead of thymine
Three forms of RNA:
a. mRNA: a single, uncoiled strand which transmits information from DNA for use in protein synthesis. it serves as the template for the assembly of amino acids during protein synthesis.
c. rRNA: found in a globular form. it is the major component of ribosomes.
1. genetic code: system that contains information needed by cells for proper functioning.
2. the genetic code is built into the arrangement of nitrogen bases in a particular sequence of DNA
2. DNA makes RNA makes proteins; therefore, DNA contains the information needed to put the amino acids together in the proper sequence
4. a specific group of three sequential bases of mRNA is called a codon.
5. it recognizes/ codes for a specific amino acid (tRNA is intermediary)
6. each mRNA codon attracts a group of bases on tRNA; the tRNA has a specific amino acid attached to it
a. universal "start" codon: AUGb. stop codon: UAA, UAG, UGA
(the production of RNA from DNA)
1. RNA polymerase binds to DNA and separates the complementary strands
2. the enzyme directs bonds to form between bases of DNA and complementary bases of RNA floating freely in the nucleus
3. next, it bonds the sugar to the phosphate.
4. the enzyme releases the RNA strand when it reaches the stop codon.
(the process of assembling proteins)
1. mRNA moves out of the nucleus by passing through the nuclear pores
2. mRNA migrates to the ribosomes
3. amino acids are transported to the ribosomes by tRNA
4. anticodon found in tRNA is complementary to the codon of mRNA
5. assembly begins when ribosome attaches to AUG (methionine) codon on mRNa
6. AUG on mRNA pairs with UAC on tRNA.
7. the ribosome moves along the mRNA translating it
8. each amino acid is linked to the chain by an enzyme
9. The process continues until the ribosome reaches a stop codon
10. the ribosome is released and the polypeptide is complete
1. The order of bases on mRNA functions in manufacturing specific proteins.
2. The base sequence of mRNA is complementary to a specific region of DNA.
3. Gene: the region of DNA that directs the formation of a polypeptide.