Download DNA_and_RNA

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
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
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