Nucleic Acids and Protein Synthesis

DNA (deoxyribonucleic acid) is…  An organic compound  A type of nucleic acid  Double stranded  Made up of subunits called NUCLEOTIDES

Nucleotides have 3 parts  Sugar molecule called DEOXYRIBOSE  PHOSPHATE GROUP  NITROGEN CONTAINING BASE

THE 4 NITROGEN CONTAINING BASES IN DNA:  ADENINE=A  GUANINE=G  CYTOSINE=C  THYMINE=T

PURINES AAAADENINE and GUANINE are PURINES BBBBases that have 2 rings of carbon and nitrogen atoms

PYRIMADINES  CYTOSINE & THYMINE are PYRIMADINES  Bases that have 1 ring of carbon and nitrogen atoms

WATSON & CRICK  WATSON & CRICK suggested that DNA is made of 2 nucleotide chains that wrap around each other to form a spiral shape called a double helix.

THE COMPLEMENTARY BASE PAIRING RULES IIIIn a double helix, cytosine pairs with guanine & adenine pairs with thymine. TTTTherefore, A=T & C=G.

REPLICATION  The copying of DNA is called REPLICATION.  The 2 nucleotide chains separate by unwinding-each chain serving as a template for a new nucleotide chain.  If the original DNA strand sequence is: A-T-T- C-C-G, the new nucleotide chain would read: T-A-A-G-G-C.  When replication is finished, 2 new exact copies of the original DNA molecule are produced & the cell is ready to undergo cell division.

DNA Replication

AAAA change in a nucleotide sequence is called a MUTATION. DDDDNA may be damaged by a variety of things, such as chemicals and ultraviolet (UV) rays from the sun.

Quick Quiz  What are the three parts of a nucleotide?  What is stated by the complimentary base pairing rules?  What is replication?

RNA (ribonucleic acid) is…  An organic compound  Type of nucleic acid  Made up of nucleotides  Single strand  URACIL (another pyrimadine) replaces thymine in RNA. This means that URACIL, not thymine, pairs with ADENINE in RNA.  U=A

Compare RNA to DNA

Types of RNA (all 3 help to make proteins) 1.MESSENGER RNA (mRNA) is made of a single, uncoiled chain. mRNA carries genetic info from the DNA in the nucleus to the cytosol of a eukaryotic cell.

Types of RNA, cont. 2. TRANSFER RNA (tRNA) is a single chain of RNA nucleotides folded into a hairpin shape that binds to specific amino acids.

3. RIBOSOMAL RNA (rRNA) is the most common RNA. rRNA is made of RNA nucleotides that are in globular form. rRNA makes up the ribosomes where proteins are made.

TRANSCRIPTION TTTThe process by which genetic info is copied from DNA to RNA AAAAll 3 types of RNA are made in this process CCCContinues until the TERMINATION SIGNAL is reached TTTThink of using a variety of colored paper in the copy machine…

TRANSCRIPTION

Recall that…  The making of proteins is called PROTEIN SYNTHESIS  PROTEINS are made of AMINO ACIDS that are linked together by PEPTIDE BONDS.  The function of the protein is decided by the amino acids that make it up.

GENETIC CODE  The relationship between a nucleotide sequence and an amino acid sequence is called the GENETIC CODE.  It is used to translate mRNA transcripts into proteins.  The genetic info needed for making proteins is encoded in a series of 3 mRNA nucleotides called a CODON.

Genetic Code, cont.  Each codon codes for a specific amino acid.  Some codons signal for translation of an mRNA to start or stop.  The START CODON (AUG) makes a ribosome start translating an mRNA molecule.  STOP CODONS (UAA, UAG, UGA) cause the ribosome to stop translating the mRNA.

Genetic Code, cont.

TRANSLATION  The process of assembling polypeptides from info encoded in the mRNA  Begins when mRNA leaves the nucleus through pores in the nuclear membrane  mRNA migrates to a ribosome where protein synthesis takes place

Translation, cont.

 Amino acids floating in the cytosol are brought to the ribosomes by the tRNA molecules  On the opposite side of the tRNA molecule (from where the amino acid is attached), there is a loop that has a sequence of 3 nucleotides called an ANTICODON.  The tRNA anticodon is complementary to and pairs with its corresponding mRNA codon.  For example, a tRNA with an anticodon of AAA would bind to the mRNA codon sequence of UUU.

Translation, cont.

Protein Assembly  Starts with start codon (AUG)  As a ribosome moves down an mRNA transcript, each mRNA codon is paired with its tRNA anticodon.  This causes an amino acid to attach, forming a peptide bond.  As each amino acid is added to the chain, the ribosome moves 3 nucleotides (1 codon) ahead on the mRNA transcript, where the next amino acid will be translated.  It ends with a stop codon.

Quick Quiz  What are two differences between RNA and DNA?  What is transcription?  What is translation?  What is the genetic code used for?