dna & genes chapter 12
Post on 15-Jan-2016
28 Views
Preview:
DESCRIPTION
TRANSCRIPT
DNA & GenesChapter 12
DNA, RNA, & Protein Synthesis
I. DNA Molecule of HeredityA. Structure
• DNA (polymer) is a long molecule made up of Nucleotides (monomers)
• A Nucleotide consists of: – Deoxyribose (a 5-carbon sugar) – a phosphate group– One of 4 Nitrogenous bases (contain nitrogen)
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)
PURINES
PYRIMIDINES
•The nitrogenous bases of DNA (purines – double ring / pyrimidines single ring)
DNA
• Deoxyribonucleic acid• Deoxyribose is sugar• Nitrogenous bases:
Adenine binds with Thymine
Cytosine binds with Guanine
One nucleotide of DNA
Structure of DNA (cont.)
• DNA is like a twisted ladder:– Rungs: complementary base pairs (A=T, G=C)– Uprights: deoxyribose and phosphate groups
• Your Turn: Match this DNA base sequence with its correct complementary DNA bases:
• T-C-G-A-A-C-T• A-G-C-T-T-G-A
DNA….who cares
Is used to determine
the paternity of
Children on shows such as:
Is used to catch criminals
Is used to make genetically modified food Is used to compare
similarities between species
Is used to make antibiotics and
vaccines
History: Griffith and Transformation
• Year: 1928• Examined 2 strains of
pneumonia bacteria– Rough– Smooth
• Injected mice with bacteria to see if they would develop pneumonia
• Discovered transformation– Took the heat killed bacteria
and combined it with the harmless bacteria, and mice developed pneumonia
History: Avery & DNA
• 1944• Used Griffith’s
experiment. He wanted to know which molecule in the heat-killed bacteria was important in transformation
• Avery used enzymes to discover that DNA was the molecule that allowed transformation to happen
History: Hershey-Chase
• 1952• The Hershey-Chase experiment
used viruses known as bacteriophages.
• Question: Wanted to know which part of the virus, protein or DNA, entered the infected core of bacterium. Preformed the experiment by using radioactive markers
• Concluded, that the genetic material was DNA
B. History
. CHARGAFF (1949): discovered that the % of Cytosine and Guanine were about the same in DNA; the same was true about Adenine and Thymine– This suggests BASE
PAIRING……….. that C bonds with G and A bonds with T!
Source of DNA
A T G C
Streptococcus 29.8 31.6 20.5 18.0
Yeast 31.3 32.9 18.7 17.1
Herring 27.8 27.5 22.2 22.6
Human 30.9 29.4 19.9 19.8
Phosphate group Deoxyribose
Purines Pyrimidines
History (cont.)
2. Wilkins and Franklin(1952): took X-Ray photographs of DNA which suggested a twisted, helical structure, 2 strands, and bases in the center
3. Watson and Crick (1953): using all the research to date, discovered the structure for DNA: A DOUBLE HELIX (with sugar-phosphate backbones and bases on the inside held together by H bonds)
More DNA info
• DNA contains information that determines an organism’s function and appearance
• Some DNA codes for proteins• DNA is located within genes
(sections of a chromosome) inside of the nucleus of every cell
Wait a minute…Does that shape remind you of any other shape you may
have seen before?
How about this portion of an apple?
DNA Flo Rider Featuring – T-Pain-less
Shawty got them apple bottom genes with the DNA (NA)
Nucleotides twisted that way
Next thing you know
Shawty got chro mo so o o o o omes
The A’s bond with the T’s and the C’s bond with the G’s (with the G’s)
Hydrogen bonds in the double helix
They start to fold (they start to fold)
Next thing you knowShawty got chro mo so o o o o omes
They start to fold (they start to fold)
DNA Replication
• DNA opens up and makes a complete copy of itself – necessary during mitosis and meiosis
• New nucleotides float in and pair in a complementary fashion – A to T, C to G and vice versa…
Figure 16.7 A model for DNA replication: the basic concept (Layer 1)
Figure 16.7 A model for DNA replication: the basic concept (Layer 2)
Figure 16.7 A model for DNA replication: the basic concept (Layer 3)
Figure 16.7 A model for DNA replication: the basic concept (Layer 4)
Semi-conservative process…
C. DNA Replication: making more DNA during the S Phase of the Cell Cycle (in the nucleus)1. The enzyme helicase unwinds DNA double helix
(breaks hydrogen bonds btwn. bases) & a replication fork is created.(Each old DNA strand will act as a template for 2 new strands to be added on)
2. Enzyme called DNA Polymerase binds to replication fork and adds free nucleotides to each old strand of DNA
3. DNA Polymerase remains attached until 2 new DNA strands are created; it “proofreads” the strands to minimize error in the process.
Chromosome Structure
Chromosome
Supercoils
Coils
Nucleosome
Histones
DNA
double
helix
Go to Section:
DNA Animation
DNA Replication (cont.)
• Diagram of DNA Replication:
II. DNA ProteinA. RNA
• RNA: Ribonucleic Acid; used to make proteins / Single-stranded -RNA (polymer) made of nucleotides (monomer): -Ribose = 5 C sugar + Phosphate group + N Base4 bases:
• Cytosine (C)• Guanine (G)• Adenine (A)• Uracil (U) – NO THYMINE in RNA!
– 3 types of RNA: 1. messenger RNA (mRNA) – single stranded transmits info from DNA to protein syn.2. transfer RNA (tRNA) - single stranded/
20 or more varieties ea. w/ ability to bond to only 1 specific AA
3. ribosomal RNA (rRNA) – globular / major component of ribosome
B. Protein Synthesis (overview)
• 2 Stages in making proteins:
1) Transcription – using DNA template to make mRNA strand
2) Translation – using mRNA strand to create polypeptides
DNA RNA ProteinTranscription Translation
1. Transcription
• The Goal of Transcription is to produce a single-stranded mRNA helix that contains information from DNA to make proteins
• How it’s done: (This happens in the Nucleus!)1. DNA strand unwinds/unzips complementary DNA strands
2. Enzyme called RNA Polymerase binds to DNA “promoter” regions and “plugs in” complementary RNA nucleotides to the DNA template.
– Example = DNA Template: ATTGGCAGT
new RNA Strand: UAACCGUCA
Transcription (cont.)
Transcription (cont.)
3. Once produced, this pre-mRNA strand breaks away when RNA polymerase reaches a sequence of bases on DNA that act as a stop sign.
• The finished product (mRNA) moves out of the Nucleus through a nuclear pore into the cytoplasm.
4. 2 DNA complementary strands rejoin
2. The Genetic Code
• How do we get proteins from mRNA strands?
• The mRNA strand must be read in groups of 3 nucleotides, called a CODON.
• Different Codons translate for different Amino acids.
Codons in mRNA
Codons in mRNA
• “Start” codon = AUG (Methionine)
• “Stop” codons = UAA, UAG, and UGA
• Example:• mRNA Strand:
• U-C-A-U-G-G-G-C-A-C-A-U-G-C-U-U-U-U-G-A-G
methionine glycine threonine cysteine phenylalanine STOP
3. Translation
• The Goal of Translation is to “translate” these mRNA codons into their amino acids to form a polypeptide.
• How it’s done:1. mRNA strand attaches to a ribosome (rRNA)2. Each mRNA codon passes through ribosome3. Free-floating Amino Acids from cytosol are brought to
ribosome by tRNA4. Each tRNA has an anticodon to match up to mRNA codons5. Amino Acids are joined as tRNA keeps bringing them6. Polypeptide chain grows until “stop” codon is reached
Translation (cont.)
• Translation
1st. mRNA strand attaches to a ribosome (rRNA)
Translation (cont.)
• Translation
2nd, Each mRNA codon passes through ribosome
Translation (cont.)
• Translation
3rd, Free-floating Amino Acids from cytosol are brought to ribosome by tRNA
Translation (cont.)
• Translation
4th, Each tRNA has an anticodon to match up to mRNA codons
Translation (cont.)
• Translation
5th, Amino Acids are joined as tRNA keeps bringing them
Translation (cont.)
• Translation
. Polypeptide chain grows until “stop” codon is reached
III. Genetic Changes: MutationsA. Types of Mutations
1. Gene Mutations: changes in nucleotides– Point Mutations
– Frameshift mutations
2. Chromosome Mutations: changes in # or structure of chromosome– Deletion
– Insertion/Duplication
– Inversion
– Translocation
1. Gene Mutations
a. Point Mutation: the substitution, addition or removal of a single nucleotide
b. Frameshift Mutations: types of point mutations that shift the “reading frame” of the genetic message
Example of Point Mutation
*image borrowed from www.science.ngfn.de/6_164.htm
Induced Point mutation in growth hormone gene causes semi-dominant dwarfism & obesity
B. Chromosome Mutations
1. Deletion……………………………
2. Insertion/Duplication…………
3. Inversion…………………………
4. Translocation…………………….
• A chromosomal mutation involves changes in the number or structure of chromosomes. Chromosomal mutations may change the locations of genes on chromosomes and even the number of copies of some genes.
• Deletion involves the loss of all or part of a chromosome.
• The opposite of a deletion is a • Duplication, in which a segment of a chromosome is
repeated. • When part of a chromosome becomes oriented in the
reverse of its usual direction, the result is an Inversion. • A Translocation occurs when part of one
chromosome breaks off and attaches to another, non-homologous, chromosome. In most cases, nonhomologous chromosomes exchange segments so that two translocations occur at the same time.
• A chromosomal mutation involves changes in the number or structure of chromosomes. Chromosomal mutations may change the locations of genes on chromosomes and even the number of copies of some genes.
• Deletion involves the loss of all or part of a chromosome.
• The opposite of a deletion is a • Duplication, in which a segment of a chromosome is
repeated. • When part of a chromosome becomes oriented in the
reverse of its usual direction, the result is an Inversion. • A Translocation occurs when part of one
chromosome breaks off and attaches to another, non-homologous, chromosome. In most cases, nonhomologous chromosomes exchange segments so that two translocations occur at the same time.
Gene Regulation in Prokaryotes
• In the absence of lactose, the repressor protein binds to the operator on DNA and inhibits transcription of lactose-processing enzymes.
• In the presence of lactose, the repressor is inhibited from binding with the operator; this all ows transcription to take place to produce lactose-processing enzymes.
The lac operon enables the production of lactose-processing enzymes in E. coli, but only when needed.
top related