DNA, RNA, and Protein Synthesis

Chapter 12Section 1-4

DNA 12-1To 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 DiscoversTransformation – 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 Stores and transmits genetic

information. Contains the blueprints for making

proteins.

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 Thymine (T) - pyrimidine Cytosine (C) - pyrimidine Guanine (G) - purine See pg. 291, Fig. 12-5

Base Pairing Rule Hydrogen Bonds

hold the nitrogenbases together in the middle

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-GSee pg. 294, Fig. 12-7

Chromosomes & DNA Replication 12-2

DNA 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. See pg. 297, Fig. 12-10Chromosomes 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 During cell reproduction an exact copy

of the parent cell DNA is made. DNA unzips (separates) into 2 strands. 2 new strands form using Base pairing. Replication results in 2 DNA

molecules, each with 1 new strand & 1 original strand.

DNA Replication

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?

Process of DNA Replication See pg. 298, Fig. 12-11

2 strands separate. Replication forks form. New strands form. New bases are added (base pairing). Ex. TACGTT = ATGCAA 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

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 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)

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.

See pg. 300, Fig. 12-12

Transcription The process in which RNA is made from DNA. Occurs inside the nucleus. mRNA leaves the nucleus and takes the

information to the RIBOSOME where a protein will be made.

RNA polymerase – enzyme that is required during transcription which binds to DNA and separates the 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.

Genetic CodeSee pg. 303, Fig. 12-17

Polypeptide – long chains which contain a combination of any or all of the 20 different amino acids which combine to form many different proteins.

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 consecutive nucleotides that specify a single amino acid to add to the polypeptide. With 4 bases, there are 64 possible 3-base codons.

Ex. This RNA sequence UCGCACGGU Read 3 bases at a time UCG-CAC-GGU Different amino acids UCG Serin - CAC Histidine – GGU Glycine

TranslationSee pg. 304-5, Fig.12-18

The process in which the cell uses information from RNA to produce proteins (protein synthesis).

Occurs on the ribosome.

Translation

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 12-4 Mutations – are changes in the

genetic material. 2 Kinds:

Gene mutations Chromosomal mutations

Gene MutationsSee pg. 307, Fig. 12-20

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 MutationsSee pg. 308, Fig. 12-21

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.