DNA, RNA AND PROTEIN SYNTHESIS Biology Corsicana High School

DNA l stands for: deoxyribonucleic acid l function: controls the production of proteins in the cell stores and uses information in the cell copies itself exactly for new cells

Structure of DNA

Nucleotide l the monomer of DNA l each consists of: deoxyribose sugar phosphate nitrogen-containing base

Bases in DNA l purines---have a double ring adenine (A) guanine (G) l pyrimidines---have a single ring thymine (T) cytosine (C)

Double Helix l structure of DNA discovered by James Watson and Francis Crick (1953) l molecule is a two-sided spiral--- like a twisted ladder

3 Keys to DNA Structure l the sides of the ladder are formed by deoxyribose and phosphate alternating l the nitrogen bases are attached to the deoxyribose on the sides

3 Keys to DNA Structure (continued) l the rungs of the ladder are formed by a pair of nitrogen bases, joined in the middle by weak hydrogen bonds A always pairs with T G always pairs with C

Complementary l the two sides of the DNA ladder are complementary l “they complete each other”

Replication l the process of duplication of a DNA molecule l occurs prior to cell division (in S phase of interphase) so that each daughter cell will have a full set of DNA

Steps in Replication l The DNA double helix “unzips”--- the hydrogen bonds between the bases break, and the molecule comes apart down the middle l This forms two single strands with bases exposed

Steps in Replication (continued) l Free nucleotides in the nucleus join up to the exposed bases, matching A-T and G-C, forming a new complementary strand for each of the original strands l Two identical DNA molecules are formed. Each is 1/2 old and 1/2 new

RNA l stands for: ribonucleic acid l primary function: uses information from DNA to synthesize proteins

3 Ways RNA Structure Differs from DNA l RNA is a single strand; DNA is a double strand l RNA has ribose sugar; DNA has deoxyribose sugar l RNA has the nitrogen base uracil (U) instead of the thymine (T) found in DNA

3 Types of RNA l messenger RNA (mRNA)---serves as a template (pattern) for the assembly of amino acids into proteins l transfer RNA (tRNA)---bonds to a specific type of amino acid and brings it to the ribosome for protein synthesis. There are 20 different varieties of tRNA l ribosomal RNA (rRNA)---globular form; a major component of the ribosome

Transcription l the process by which RNA is produced from DNA l occurs in the nucleus of the cell

Steps in Transcription l DNA double helix in nucleus unzips l Free RNA nucleotides match up to exposed DNA bases, matching A-T, U-A, G-C, C-G. The RNA nucleotides are complementary to the DNA bases

Steps in Transcription (continued) l This forms a single RNA strand (mRNA) which now has the DNA code in RNA bases l mRNA releases from the DNA and leaves the nucleus. The DNA snaps back together

Protein Synthesis l the formation of proteins in the cell, using information coded on DNA, and carried out by RNA

Structure of a Protein l made of 1 or more polypeptide chains, each consisting of a specific sequence of amino acids l a protein consists of hundreds or thousands of amino acids joined together in a very specific sequence

Genetic Code l the system that contains information needed by cells for proper functioning l triplet code---3 DNA bases code for 1 amino acid l codon---a specific group of 3 sequential bases for mRNA l universal start codon = AUG

Translation l the process of assembling protein molecules from information encoded in messenger RNA l occurs at the ribosome

Steps of Translation l mRNA (that was formed from DNA in the nucleus by transcription) attaches to the ribosome l tRNA picks up specific amino acid in cytoplasm and brings it to the ribosome anticodon---a group of 3 tRNA bases that are complementary to the mRNA codon

Steps of Translation (continued) l tRNA anticodon matches up to mRNA codon at the ribosome. This puts the amino acid in the proper place l a peptide bond forms between amino acids in sequence. l The ribosome moves down to the next mRNA codon and another tRNA matches to it

Steps of Translation (continued) l tRNA detaches and goes to pick up another amino acid l continues down the mRNA strand until a stop codon is reached, forming a chain of amino acids---a polypeptide

Gene l the region of DNA that directs the formation of a particular polypeptide

Code Transfers DNAmRNA tRNA amino acid (triplet code) (codon) (anti- codon)