DNA AND PROTEIN SYNTHESIS 2008 DNA DEOXYRIBONUCLEIC ACID
DNA AND PROTEIN SYNTHESIS 2008
DNA (DEOXYRIBONUCLEIC ACID) • Nucleic acid that composes chromosomes and carries genetic information.
CHROMOSOME ORGANIZATION 1. A chromosome is an enormous strand of super coiled DNA. 2. Sections of DNA on the chromosome that code for proteins are called genes. 3. Noncoding sections of DNA are called “junk DNA” (regulatory or unknown function)
BUILDING BLOCKS OF DNA Composed of nucleotides • Nucleotides contain three parts: 1. 5 -Carbon Sugar (deoxyribose) 2. Phosphate Group 3. Nitrogen Base (four types, adenine, guanine, thymine and cytosine)
• Specific base pairing arrangement (Chargaff’s Rule) A-T C-G • The amount of adenine = amount of thymine • The amount of guanine = amount of cytosine
STRUCTURE OF DNA • Consists of two strands of nucleotides that form a twisted ladder (double helix) • Sugar and phosphate alternate along the sides of the ladder (linked by strong covalent bonds) • Pairs of nitrogen bases form the rungs of the ladder (linked by weak hydrogen bonds). • The structure of DNA was discovered by Watson and Crick.
FUNCTION OF DNA • DNA codes for proteins (structural proteins, enzymes, and hormones) • information for building proteins is carried in the sequence of nitrogen bases • proteins determine physical and metabolic traits and regulate growth and development.
DNA REPLICATION Process in which DNA is copied
PURPOSE OF DNA REPLICATION Gives daughter cells produced by cell division a complete set of genetic information identical to the parent cell.
WHERE REPLICATION OCCURS Nucleus
WHEN DURING THE CELL CYCLE REPLICATION OCCURS Interphase (S)
HOW REPLICATION OCCURS 1. Helicase enzymes unzip the parent strand by separating the nitrogen base pairs. 2. DNA polymerase pairs free DNA nucleotides with the exposed bases on both strands following the base pair rules. • each strand from the parent molecule serve as a template
3. Hydrogen bonds reform spontaneously sealing the two strands of each DNA molecule together.
RESULTS OF REPLICATION • Two molecules of DNA that are identical • Each is half old (strand from parent) and half new (strand synthesized by DNA polymerase) • Few mistakes are made (semiconservative process)
Think about it… • If 30% adenine is present in an organism, then what is the percentage of thymine? • What is the remain percentage of nitrogen bases? • What percent of the remaining is cytosine? How do you know?
Think about it • 30% thymine • 40% remaining • 20% cytosine (same amt of cytosine as guanine, and adenine and thymine make up 60% of organisms nitrogen bases)
RNA (RIBONUCLEIC ACID) Nucleic acid involved in the synthesis of proteins Subunits are nucleotides Nucleotides are composed of ribose sugar, phosphate and a nitrogen base
RNA STRUCTURE Differs from DNA in three ways. 1. Single strand of nucleotides instead of double stranded 2. Has uracil instead of thymine 3. Contains ribose instead of deoxyribose
RNA FUNCTION Three forms of RNA involved in protein synthesis 1. m. RNA (messenger): copies instructions in DNA and carries these to the ribosome. 2. t. RNA (transfer): carries amino acids to the ribosome. 3. r. RNA (ribosomal): composes the ribosome.
COMPARING DNA AND RNA DNA Role Complete instructions for making proteins Transfer of information-protein production Type of molecule Nucleic acid Building Blocks Nucleotides Strand # 2 1 Sugar deoxyribose Location Nucleus Cytoplasm Nitrogen Base Pairs ACTG ACUG Types Only one m. RNA r. RNA t. RNA
PROTEIN SYNTHESIS Cells build proteins following instructions coded in genes (DNA). • Consists of two parts, transcription and translation
TRANSCRIPTION DNA is copied into a complementary strand of m. RNA. WHY? • DNA cannot leave the nucleus. Proteins are made in the cytoplasm. m. RNA serves as a “messenger” and carries the protein building instructions to the ribosomes in the cytoplasm.
LOCATION OF TRANSCRIPTION Nucleus
HOW TRANSCRIPTION OCCURS 1. RNA polymerase untwists and unzips a section of DNA (usually a single gene) from a chromosome.
2. RNA polymerase pairs free RNA nucleotides to the exposed bases of one of the DNA strands following base pair rules. • Uracil replaces thymine • Only 1 strand of DNA serves as a template, the other “hangs out”
3. Newly synthesized m. RNA separates from template DNA and DNA zips back up.
RESULT OF TRANSCRIPTION m. RNA strand with instructions for building a protein that leaves the nucleus and goes to the cytoplasm.
TRANSCRIPTION EXAMPLE • Transcribe the following DNA Sequence in m. RNA TAC CGG ATC CTA GGA TCA AUG GCC UAG GAU CCU AGU
PROTEINS Structural and functional components of organisms. • Composed of amino acids • order of nucleotides in DNA determines order of amino acids in a protein • One gene codes for one protein
GENETIC CODE The “language” that translates the sequence of nitrogen bases in DNA (m. RNA) into the amino acids of a protein. • Codon = three nucleotides on DNA or m. RNA • One codon specifies one amino acid • Some codons are redundant (code for the same amino acid) • The genetic code is universal to all organisms
DNA: TAC CTT GTG CAT GGG ATC m. RNA AUG GAA CAC GUA CCC UAG A. A MET G. A HIS VAL PRO STOP
IMPORTANT CODONS • AUG = start translation (Met) • UAA, UAG, UGA= stop translation
TRANSLATION Instructions in m. RNA are used to build a protein
LOCATION OF TRANSLATION ribosome (in the cytoplasm)
PROCESS OF TRANSLATION 1. m. RNA binds to the ribosome. 2. Ribosome searches for start codon (AUG) 3. t. RNA brings correct amino acid (methionine) to the ribosome. • Each t. RNA carries one type of amino acid. • The anticodon (three nitrogen bases on t. RNA) must complement codon for amino acid to be added to protein chain
4. ribosome reads next codon 5. t. RNAs continue lining up amino acids according to codons 6. peptide bonds link amino acids together 7. ribosome reaches STOP codon • Amino acid chain is released
RESULT OF TRANSLATION A Protein
Review Protein Synthesis
Practice online • http: //learn. genetics. utah. edu/conte nt/begin/dna/transcribe/
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