DNA STRUCTURE AND REPLICATION Molecular Genetics DNA Molecule

DNA STRUCTURE AND REPLICATION Molecular Genetics

DNA Molecule

Mitosis DNA - Deoxyribonucleic Acid a long thin molecule that controls an organism’s traits DNA is about 100, 000 x the diameter of the nucleus 2 meters (6 feet) of DNA needs to fit in each nucleus Like stuffing 113 miles of string in a basketball (Worcester to Hartford and back)

DNA Structure DNA - Deoxyribonucleic Acid; made up of four nucleotides in a double helix shape Adenine (A) Guanine (G) Thymine (T) Cytosine (C)

DNA Stucture Nucleotides pair together to form a double helix through hydrogen bonds A – T; C – G

Cell Division How does all that DNA fit inside the nucleus? DNA coils itself very tightly around histones (proteins that help DNA stay tightly packed) Chromatid - Super-coiled DNA that copies itself before cell division Chromosome - 2 chromatids (identical copies) held together by a centromere

Cell Division How is the DNA coiled up in a chromosome? See a movie here.

Cell Division How many chromosomes does a human cell have? 46 total (23 identical pairs) 44 (22 identical pairs) of autosomes and 2 (1 pair) of sex chromosomes

Cell Division Are there exceptions to the number of chromosomes? Sperm and eggs have 23 chromosomes (one of each). This is normal; referred to as ‘haploid’ (half chromosomes) while other cells are called ‘diploid’ Down syndrome (47 chromosomes; extra chromosome 21)

Cell Division Are there exceptions to the number of chromosomes? Turner’s syndrome (45 chromosomes; females lack one X chromosome)

DNA Replication When does DNA replication happen? DNA replicates during the S phase of the cell cycle.

DNA Replication What are the 3 hypothesis for DNA replication? Conservative Model Semiconservative Model Conservative Model

Semiconservative Model of DNA Replication DNA replicates through the Semiconservative Model. 1. DNA unwinds and strands are pulled apart 2. Nucleotides are added to each strand until there are two double helixes of DNA.

DNA Replication What really happens during DNA replication?

DNA Replication What really happens during DNA replication?

DNA Replication Find the complimentary base pairs to the DNA sequence: 1. TAC AGG ATC TTA CGT AAG TCC GTA ACT 2. TAC CCC GTG ATG CCA TGC AAG TAG ACT REMEMBER: A→T T →A C →G G →C

Transcription & Translation Transcription Translation To copy something DNA → m. RNA To go from one language to another m. RNA → Protein (amino acids)

Transcription & Translation What is RNA? m. RNA • RNA is ribonucleic acid. • Made up of one strand of nucleic acids • Uses Uracil (U) instead of Thymine (T) • A →U (NOT A→T) • There are 3 types • Messenger RNA • RNA that is made during Transcription and used as a template for Translation r. RNA • Ribosomal RNA • Makes the ribosome • Where m. RNA→protein t. RNA • Transfer RNA • Brings amino acids to Ribosome

Transcription Steps in Transcription In the nucleus… 1. DNA unwinds where RNA polymerase binds to it. 2. Complementary RNA nucleotides are added by RNA Polymerase. A chain of m. RNA grows. 3. RNA polymerase reaches a stop signal in the DNA and releases the m. RNA chain and the DNA rewinds. m. RNA leaves the nucleus. Product = m. RNA chain

Transcription Transcribe this sequence of DNA: TAC AGG ATC TTA CGT AAG TCC GTA ACT REMEMBER: A→U T →A C →G G →C

Transcription Transcribe this sequence of DNA: TAC GTA CCT ATT CGA GTG CAA CAT ACT REMEMBER: A→U T →A C →G G →C

Transcription Transcribe this sequence of DNA: TAC GGG CTA TTA AAC CGT TGC ATA ACT REMEMBER: A→U T →A C →G G →C

Translation What are the steps for Translation? In the cytoplasm… 1. Ribosome assembles around m. RNA 2. t. RNA brings amino acids to ribosome to add to growing protein. 3. “STOP! “ codon is reached in m. RNA. Protein is released. Ribosome disassembles. m. RNA disintegrates. Product = protein

Translation How does t. RNA know which amino acid to add? codon CODONS! A group of 3 nucleotides (3 letters) in m. RNA TAC AGG ATC TTA CGT AAG TCC GTA ACT CODON!

Translation How do I figure out which amino acid codes with which codon? Wobble Third letter in codon can change without changing the amino acid

Translation Translate this sequence of DNA: TAC AGG ATC TTA CGT AAG TCC GTA ACT REMEMBER: A→U T →A C →G G →C p 207 – codon chart

Translation Translate this sequence of DNA: TAC GTA CCT ATT CGA GTG CAA CAT ACT REMEMBER: A→U T →A C →G G →C

Translation Translate this sequence of DNA: TAC GGG CTA TTA AAC CGT TGC ATA ACT REMEMBER: A→U T →A C →G G →C