DNA Structure, Replication, Transcription, and Translation PDF

DNA Structure  DNA – Deoxyribonucleic Acid  Consists of nucleotides  Each nucleotide composed of a phosphate group, a sugar (deoxyribose) and a nitrogenous base  Four possible bases : ADENINE, GUANINE, CYTOSINE , THYMINE (A,G,C,T) https:// www.youtube.com/watch?v=wxqDe-IHSuQ Double...

DNA Structure  DNA – Deoxyribonucleic Acid  Consists of nucleotides  Each nucleotide composed of a phosphate group, a sugar (deoxyribose) and a nitrogenous base  Four possible bases : ADENINE, GUANINE, CYTOSINE , THYMINE (A,G,C,T) https:// www.youtube.com/watch?v=wxqDe-IHSuQ Double helix of DNA molecule  DNA composed of TWO strands  Each strand shaped like a spiral staircase  Nucleotides in each strand covalently bonded together  Base pairs are complementary to each other (Adenine-Thymine and Guanine and Cytosine) Label all parts of the DNA molecule Structure of RNA Comparison of the structure of DNA and RNA DNA RNA Contains the five-carbon Contains the five carbon sugar deoxyribose. sugar ribose. Contains the bases Contains the bases adenine, guanine, adenine, guanine, cytosine and thymine. cytosine and uracil (instead of thymine). A double-stranded A single-stranded molecule. molecule. DNA Replication  DNA needs to be replicated (doubled) for cell division  Quantity of DNA doubled and exact copy of each DNA molecule made.  Takes place during INTERPHASE of the cell cycle  Nuclear membrane present, DNA in the form of chromatin (not chromosomes)  Molecules present include: enzymes (helicase and DNA polymerase), free nucleotides Process of Replication  Unwinding and “unzipping” of the two DNA strands.  HELICASE breaks hydrogen bonds between complimentary base pairs  Unpaired nucleotides on single strands used as a template  Free-floating nucleotides form complimentary pairs with the single-stranded nucleotides of the unzipped DNA molecule  Formation of a covalent bond between two adjoining nucleotides catalysed by enzyme DNA POLYMERASE  New complimentary strands formed in opposite directions  Complimentary base pairing ensures two identical strands after replication  Replication described as SEMI-CONSERVATIVE  DNA Replication http://highered.mheducation.com/olc/dl/120076/bio23.swf Comparison between DNA and RNA DNA RNA Contains a 5-carbon sugar Contains a 5-carbon sugar Sugar is deoxyribose Sugar is ribose Each nucleotide has one of four Each nucleotide also has one of nitrogenous bases four nitrogenous bases Bases include: Adenine, Thymine, Bases include Adenine, Uracil, Guanine and Cytosine Guanine and Cytosine Double stranded molecule Single stranded molecule Protein Synthesis  DNA controls the proteins made in a cell  Some of the proteins produced are enzymes  Affect overall biochemistry of cell  DNA indirectly controls the biochemistry of carbohydrates, lipids and nucleic acids by the production of enzymes  Protein synthesis consists of two major sets of reactions: TRANSCRIPTION and TRANSLATION  Both either produce or require RNA (Ribonucleic acid) Transcription produces RNA molecules  Sections of DNA that code for polypeptides are called GENES  A gene is a specific sequence of nitrogenous bases found in a specific location in a DNA molecule  DNA found inside nucleus, proteins are formed in the cytoplasm outside nucleus.  Messenger RNA (mRNA) copies and carry DNA message (code) to the cytoplasm (where enzymes, ribosomes and amino acids are found)  Nucleoplasm contains free nucleotides (DNA and RNA) Process of Transcription  Process begins when an area of DNA of one gene becomes unzipped  Two complimentary strands of DNA are now single- stranded  One of the two DNA strands used as a template to create the mRNA molecule (enzyme RNA polymerase used as catalyst for process)  As RNA polymerase moves along the DNA strand, RNA nucleotides float into place by complimentary base pairing  Transcribed mRNA molecule floats in nucleoplasm and enters cytoplasm through nuclear pores. Genetic code and types of RNA  Three bases (triplet) is enough to code for an amino acid  These are known as CODONS or CODON TRIPLET  Three different types of RNA molecules  They are all single-stranded and each is transcribed from a gene of DNA.  mRNA- complimentary copy of a DNA gene  rRNA- each ribosome composed of rRNA and ribosomal protein tRNA- transfers 1 of the 20 amino acids to the ribosome for polypeptide formation http:// highered.mcgrawhill.com/sites/0072507470/student_view0/chapter3/ani mation __mrna_synthesis__transcription___quiz_1_.html Process of Translation  mRNA locate and align with a ribosome.  Specific tRNA (anticodon complementary to codon triplet of mRNA)  Second tRNA brings in a second amino acid ( anticodon matches second codon triplet of mRNA)  An enzyme catalyses a condensation reaction between the two amino acids forming a peptide bond (covalent bond)  Bond between first tRNA molecule and amino acid it transferred in, is broken (tRNA released)  Process continues until the ribosome gets to the last codon triplet (STOP CODON) http:// highered.mcgrawhill.com/sites/0072507470/student_view0/ch apter3/animation __protein_synthesis__quiz_3_.html