dna, rna, and protein synthesis. dna to understand genetics, biologists had to learn the chemical...
TRANSCRIPT
DNA, RNA, and Protein Synthesis
DNA
To understand genetics, biologists had to learn the chemical structure of genes.
Frederick Griffith- 1928; He tried to figure out how bacteria makes people sick like pneumonia. He injected mice with a mixture of heat-killed bacteria, disease-causing bacteria, & live harmless bacteria. The result was that the mice developed pneumonia.
Griffith Discovers
Transformation – disease causing bacteria pass the disease causing ability on to the harmless strain of bacteria.
One permanently changed another.
Other Scientists
Oswald Avery – 1944; He & his research group repeated Griffith’s work and found that bacteria are transformed by DNA.
That DNA stores and transmits the genetic information from one generation of an organism to the next.
Other Scientist
Alfred Hershey & Martha Chase – 1952; They performed experiments with bacteriophages & showed that genes are made of DNA.
Other Scientist
James Watson and Francis Crick created the first double helix model. ( they eventually won the nobel prize for it in 1962 for their work)
Rosalind Franklin also played a major role in the ladder’s discovery because Watson and Crick used her photos of the DNA ladder to assemble the model. (Unfortunately she died 4 years before nobel prize was awarded)
Pictures of Watson and Crick, Rosalind Franklin and her X-ray
photos of DNA
Hershey & Chase
Bacteriophage – “bacteria eater”; a kind of virus that infects bacteria. See pg. 289, Fig. 12-3
Radioactive Markers – used by Hershey & Chase to determine which part of the virus (protein coat or the DNA coat) entered the infected cell. As a result, they could learn whether genes were made of protein or DNA.
32P & 35S – Phosphorous 32 is not often found in protein and Sulfur 35 in not found in DNA. The presence of 35S in bacteria means that the viruses’
protein was in the bacteria. The presence of 32P in bacteria means the DNA was in the
bacteria. Conclusion – Genetic material of bacteriophage was DNA,
not protein.
What is DNA?
Deoxyribonucleic acid is the nucleic acid stores the genetic code. Contains the blueprints for making
proteins. Genetic codes: “program” of the cells;
how cells store information they pass from one generation to the next.
DNA is a polymer (large molecule)formed from units called nucleotides.
Location & Structure of DNA
Location: in the nucleus of eukaryotic cells. In the cytoplasm of prokaryotic cells.
Structure: Double stranded (double helix) Composed of 3 part nucleotides:
Deoxyribose (5 carbon sugar) Phosphate group (PO4) Note: The two alternate S-P-S-P with the nitrogen bases
always lined up on the Sugars (deoxyribose) Nitrogen base (1 of 4)
Adenine (A) – purine Guanine (G) - purine Thymine (T) – pyrimidine Cytosine (C) - pyrimidine
Base Pairing Rule
Hydrogen Bonds hold the nitrogenbases together in the middle
Adenine pairs with Thymine Cytosine pairs with Guanine
Structure cont.
Purines – have 2 rings in their structure. Pyrimidines – have 1 ring in their structure. Double Helix – 2 strands wound around
each other; twisted ladder. Base pairing – hydrogen bonds hold 2
strands together & can form between certain base pairs. A-T, T-A, G-C, C-G
Discovered by Watson & Crick and won a nobel prize.
Chromosomes & DNA Replication (synthesis) 12-
2DNA is very long & must fold up tightly to fit inside a cell.
Ex. Trying to pack a 300m length rope into a backpack.Chromosome Structure: DNA is wound around proteins. DNA & proteins wind together to form
nucleosomes. Nucleosomes pack together to form thick fiber.Chromosomes contain DNA & proteins called histones.Most of the time nucleosomes are spread out & the
chromosomes are not visible but during mitosis, the nucleosomes become more tightly packed & the chromosomes can be seen under a microscope.
DNA Replication
Each strand of DNA serves as a template for a new strand of DNA
During cell reproduction an exact copy of the parent cell DNA is made.
Enzymes unzip DNA (separates) breaking hydrogen bonds between bases.
2 strands unwind. 2 new strands form using Base pairing. DNA replicates itself exactly so that each new cell will
have an identical copy of the original DNA.Example: template DNA: TACGTT new DNA: ATGCAA
DNA Replication
Process of DNA Replication
2 strands separate. Replication forks form. New strands form. New bases are added (base pairing). Ex. TACGTT = ATGCAA
It is semi-conservative- 2 DNA molecules identical to each other &
to the original molecule.DNA polymerase – enzyme that unzips DNA molecules when
hydrogen bonds b/w the base pairs are broken. 2 strands unwind & join nucleotides.
Can you write the corresponding Nitrogen
Base?1. GAC TAT ATT GAC ATT GAG CCC
TTA
2. ATA GAG CAC GCA TAT CCG AGT TAT
Replication animation
http://media.pearsoncmg.com/bc/bc_0media_ap/apflix/ap/ap_video_player.html?dna
Making Proteins
DNA contains the instructions for building proteins
Proteins are made at the ribosomes
DNA cannot leave the nucleus How does DNA’s information get to
the ribosome?
RNA & Protein Synthesis 12-3
Genes – coded DNA which contain instructions for assembling proteins.
The first step in decoding the genetic messages is to copy part of the nucleotide sequence from DNA into RNA.
What is RNA?
Ribonucleic acid mRNA –nucleic acid that acts as a messenger
b/w DNA & ribosomes & carries the genetic code for making proteins from the amino acids.
RNA is a disposable copy of a segment of DNA. RNA has 1 job – (protein synthesis) controlling
the assembly of amino acids into proteins. Contains coded information for making
proteins.
Location & Structure of RNA
Location: In the nucleus Cytoplasm Ribosome
Structure: Single Strand Nucleotides composed of:
Ribose (5-carbon sugar) Phosphate group Nitrogen bases:
Adenine (A) Guanine (G) Cytosine (C) Uracil (U)
RNA does not contain thymine but has uracil
3 Types of RNAAll are involved in Protein Synthesis & are copied
from the DNA
Messenger RNA – (mRNA) carry copies from DNA to rest of cell.
Ribosomal RNA – (rRNA) it is on the ribosomes where proteins are assembled.
Transfer RNA – (tRNA) transfers each amino acid to the ribosome according to the coded messages in mRNA.
Why make proteins?
Needed for cell structure and movement, makes enzymes and nucleotides.
Transcription
The process in which a molecule of DNA is copied into a complementary strand of RNA.
Occurs inside the nucleus b/c DNA is in the nucleus & cant leave so a messenger RNA (mRNA) must bring the genetic information from the nucleus to the ribosomes in the cytoplasm.
Steps: RNA polymerase – enzyme that attaches to DNA & moves
along it unwinding the two strands Promoters – signals in the DNA that indicate to the RNA
polymerase where to bind.The instructions for making proteins are specified by genes & are found in the 4
nitrogenous bases.Example: DNA TGCACGCA mRNA ACGUGCGU
Transcription animation
http://www.pearsonsuccessnet.com/snpapp/iText/products/0-13-190404-3/bm/vadnatra.html
STILL CONFUSED?
Imagine that you are a mechanic. The repair manual that you use is the DNA ladder.
If you wanted to copy the instructions to install a radio in your car, would you copy the entire repair manual?
NO!!! You would only copy the portion pertaining to installing the radio. That is what transcription does.
Genetic Code
The genetic code is read 3 letters at a time, 3 bases long. Proteins are determined by the order in which amino
acids are joined together Codon – 3 letter word composed of 3 nucleotides on
mRNA Each codon codes for a particular amino acid while
chains of amino acids form proteins. With 4 bases, there are 64 possible 3-base codons &
there can be more than 1 codon for each amino acid. There are start and a stop codons. Ex. This RNA sequence UCGCACGGU Read 3 bases at a time UCG-CAC-GGU Different amino acids UCG Serin - CAC Histidine – GGU
Glycine
Translation
The process of building a protein molecule according to code in mRNA.
During the process transfer RNA (tRNA) carries amino acids to the ribosomes where the amino acids are joined to form the protein
Ribosomes are where proteins are made.
Translation
Steps of translation: tRNA binds to the mRNA A “start” codon starts the protein chain tRNA contain 3 complementary nucleotides to
the mRNA called the anticodon; once it matches it leaves behind an amino acid and the next codon is read.
more tRNA molecules will come together to create the next polypeptide
Once a “stop” codon is read, the new polypeptide chain is released as a new protein.
Translation
Translation animation
http://www.pearsonsuccessnet.com/snpapp/iText/products/0-13-190404-3/bm/vaprotei.html
What happens to mRNA at the ribosome?
mRNA is transcribed from the DNA in the nucleus. mRNA moves into the cytoplasm & attaches to a
ribosome. tRNA will read mRNA in 3 part sections (codons). tRNA carries amino acids to the ribosome. A polypeptide assembly line forms. Amino acids bond to form proteins.
Role of RNA & DNA
Compare RNA & DNA to Builders:A master plan has all the information needed to
construct a building. But builders never bring the valuable master plan to the site where it could get damaged or lost. They prepare inexpensive, disposable copies of the plan called blueprints. The master plan is safe inside the office while the blueprints are taken to the job site. Similarly, the cell uses the vital DNA “master plan” to prepare the RNA “blueprints”. The DNA is safe in the nucleus, while the RNA goes to the protein-building sites in the cytoplasm – the ribosomes.
Mutations
Mutations – are changes in the genetic material.
2 Kinds: Gene mutations Chromosomal mutations
Gene Mutations
Produce changes in a single cell. Types:
Point mutations – involves changes in one or a few nucleotides and occur at a single point in the DNA sequence.
Substitutions – one base is changed to another; only affects a single amino acid.
Insertions & Deletions– a base is inserted or removed from the DNA sequence; much more dramatic because the genetic code is read in 3-base codons.
Frameshift mutations – the shifting of codons & the “reading frame” which may change every amino acid that follows the point of the mutation. It can alter a protein so much that it is unable to perform its normal functions.
Chromosomal Mutations
Produce changes in whole chromosomes. Types:
Deletions – involve the loss of all or part of a chromosome.
Duplications – produces extra copies of parts of a chromosome.
Inversions – reverse the direction of parts of a chromosome.
Translocation – when part of one chromosome breaks off & attaches to another.