DNA and RNA Structure of DNA Chromosomes and Replication Transcription and Translation Mutation and Gene Regulation

Experiments leading to DNA structure Griffith – genetic information can be transferred from one organism to another Avery – discovered that DNA is the transforming factor for genetic information Hershey-Chase – concluded that DNA is the genetic material, not proteins Watson, Crick, Franklin – used X-ray diffraction to show the structure of DNA

Components of DNA Nucleotide – made of a 5 carbon sugar, a phosphate group, and a nitrogenous base Purines – nucleotides containing two rings in their base (adenine and guanine) Pyrimidines – nucleotides containing one ring in their base (cytosine, uracil and thymine)

Components of DNA

Chargaff’s Rules of base pairing Adenine always pairs with thymine (A-T) Guanine always pairs with cytosine (G-C)

Chromosomes and DNA Prokaryotes have a circular DNA molecule that is located in the cytoplasm. Eukaryotes have a huge DNA molecule located on the chromosomes within the nucleus.

Chromosomes and DNA Chromosomes are the structures containing genetic information (humans have 23 pairs) Chromatin – DNA and protein tightly packed together Histones – spherical protein in which DNA is wrapped around. Nucleosome – DNA and histone complex

Chromosomes and DNA

Replication Replication – the process of DNA copying itself During DNA replication, the DNA molecules separates into two strands, then produces two new complementary strands following the base pairing rules. Each strand of the double helix of DNA serves as a template, or model for the new strand.

Replication Enzymes unzip the DNA molecule by breaking the hydrogen bonds. DNA polymerase joins nucleotides to template strand. It also “proofreads” to ensure accuracy.

RNA Ribonucleic acid – single stranded nucleotide molecule, contains ribose instead of deoxyribose and uracil instead of thymine. Messanger RNA (mRNA) – carries copies of instructions for assembling amino acids Ribosomal RNA (rRNA) – contained on the ribosomes Transfer RNA (tRNA) – transfers each amino acid to the ribosome as coded by mRNA

Transcription The process of constructing mRNA from a DNA molecule. RNA polymerase binds to DNA and separates the strands. RNA polymerase uses one strand of DNA as a template to assemble nucleotides of the mRNA Promoters – specific base sequences in DNA that indicate to the enzyme where to make RNA.

Transcription Introns – segments of nucleotides not involved in coding for proteins Exons – segments of nucleotides that are expressed in protein synthesis Codon – three consecutive nucelotides that specify a single amino acid

Transcription DNA: ATCGGCACTGGC mRNA: UAGCCGUGACCG DNA: CGATCTACGCCGTAC mRNA: GCUAGAUGCGGCAUG DNA: AATCTGCAGCCATTC mRNA: UUAGACGUCGGUAAG

Translation The process of decoding a mRNA into a polypeptide chain Translation begins when mRNA attaches to a ribosome. mRNA contains a “start” codon to begin protein assembly. Each codon matches with an anticodon on a tRNA that contains amino acid. Enzymes join amino acids until reaching a “stop” codon and ribosome detaches.

Translation

mRNA: AUGCGUACCUUA protein: met-arg-thr-leu mRNA: UUCCAAGGCAAC protein: ala-glu-gly-asp mRNA: ACAUACCCCGCG protein: thr-tyr-pro-ala

Mutations Changes in the genetic material Point mutation – gene mutations involving changes in one or a few nucleotides Frameshift mutation – insertions or deletions that can shift the reading of the codons Polyploidy – condition in which an organism has an extra set of chromosomes

Gene regulation Operon – a group of genes that operate together The lac genes are turned off by repressors and turned on by the presence of lactose. (Occurs in bacterium). In eukaryotes, “TATA” box, series of adenines and thymines, that help position RNA polymerase. Enhancer sequences will also bind to proteins to begin the process of transcription Hox genes – series of genes that control the differential of cells in the embryo