Molecular Genetics

Question 1

Griffith

Answer 1

(Transforming Factor) Heat-Kills S pneumococcus can transfer a factor to live R pnemococcus that transforms R cells to S cells

-Griffith, was the first experiment suggesting that bacteria are capable of transferring genetic information through a process known as transformation.

Question 2

Avery, MacLeod and McCarty (1944)

Answer 2

(transforming factor) The pneumococcus transforming factor is DNA not protein

Question 3

Evidence to build model

Answer 3

1. Nucelotide Structure 2. Chargaff’s Rules 3. X-Ray diffraction data

Question 4

Nucleotide Structure

Answer 4

Deoxyribose+phosphoric acid+nitrogenous base(Adenine, Thymine, Cytosine, Guanine)/ Dna was known to be a nucleotide polymer

Question 5

Chargaff’s Rules

Answer 5

Adenine=Thymine Cytosine=Gunanine -Purines (A,G)=Pyrimidines(T,C,U)
-Quantities of different bases is a characteristic of a species

Question 6

Features of Watson-Crick Model (1953)

Answer 6

1. Double Helix
2. Backbones of each strand in helix is alternating phosphate and deoxyribose molecules
3. Nucleotide base pairs (consequently the strands of double helix) are held together by hydrogen bonds
4. Strands of helix are antiparallel in orientation

Question 7

Melson and Stahl

Answer 7

Demonstrated that DNA replication is semiconservative. Each newly synthesized DNA double helix is half old and half new

Question 8

Be aware of

Answer 8

1. DNA polymerase complex reads 3’ to 5’; new strands are made starting at their 5’ ends
2. energy supplied by triphosphate nucleotides are ATP, GTP
3. DNA replication is accurate, but able to repair or occasionaly incorporate errors (Mutations are an important source of genetic variability that promote evolutionary change)

Question 9

Flow of Genetic Information

Answer 9

• DNA goes back to replication. Replication ensures that all cells recieves a complete copy of genome
• Transcription makes DNA to RNA. Provides a means for portions of DNA to be copied as need and to transport that information to other parts of the cell (Happens in the nucleus)
• Translation turns RNA into Proteins. bridge between nucleic acids and proteins; converts genetic information into functional molecules used in cells (happens in the cytoplasm)

Question 10

Transcription

Answer 10

DNA to RNA
1. Read anti-sense (source of protein code) strand of DNA using RNA polymerase

2. . Begins at site in DNA at 3’ end of anti-sense strand of gene which is called promoter (RNA polymerase binding site
3. Produces all type of RNA; messenger, ribosomal, and transfer

Question 11

Messenger RNA

Answer 11

• called mRNA
• linear molecules which contain codons (triplets of nucleotides which are the genetic code words). Transcribed from structural genes
• carries the coded information for making specific proteins from DNA to ribosomes, where proteins are synthesized.

Question 12

Ribosomal RNA

Answer 12

• called rRNA
• varied RNAs which found in robosomes; ribosomes provide structural framework for translation or cellular machinery for protein synthesis

Question 13

Transfer RNA

Answer 13

tRNA; small highly folded RNA molecules of 75 to 80 bases in length.

• Each contains two important sites
  
  • the anti codon (complementary base pairing to codon) and the aminoacyl site (binding site for specific amino acids)
• involved in protein synthesis
• recognize the specific codons and transport the required amino acids.

Question 14

Prokaryote transcription

Answer 14

Straight read through of anti-sense strand; no extensive post-transcriptional processing occurs

Question 15

Eukaryote transcription

Answer 15

reads introns and exons to produce transcript which is then processed to cleave out introns; 5’cap and 3’ poly A tails are added to generate final mRNA

Question 16

Translation

Answer 16

Translation RNA—–>Protein

Components needed

1. messenger RNA with codons
2. ribosomes
3. Pool of transfer RNAs and amino acids
4. ATP

Stages: Initiation, Chain Elongation, and Termination to pay

Question 17

Stages of Translation

Answer 17

Initiation: find start codon on mRNA, attach tRNA, attach ribosome subunits; initiator tRNA will be in P site of ribosome

Chain elongation: read successive codons on mRNA as they move into A site of ribosome; new tRNAs bring needed amino acids to A site and the new amino acid is added to peptide chain; old tRNA with peptide chain attached moves to P site and ribosome shifts to read next codon; oldest tRNA leaves E site.

Termination: read stop codon in A site; all components dissociate; new peptide is released

Question 18

Genetic Code

Answer 18

Genetic Code 1. Alphabet of genetic code= nucleotide bases; “four letters”

2. Code bust be able to translate to 20 amino acids so
   a. if 1 base—-> 1 amino acid there would be only 4 usable amino acids 4^1 is 4.

b. if 2 bases —-> 1 amino acid there would be only 16 usable amino acids 4^2 is 16.

C. if 3 bases—-> 1 mino acid there would be 64 possible code words or codons 4^3=64. more than enough code words, but some amino acids have more than one codon (genetic code is redubdant), and these codons tend to be similar ex. UUU and UUC both encode phe (genetic code is degenerate)

3. Codons are triplets of bases that stand for start or stop signals or for amino acids; sense codons represent amino acids

Question 19

Genetic Code Chart 8.8

Answer 19

The Genetic Code Chart 8.8

• There is 64 possible codons but only 20 amino acids. This means that most amino acids are signaled by several alternative codons (Degeneracy) of code
  
  • allows for a certain amount of misreading of, or mutation in, the DNA without affecting the protein ultimately produced
• out of the 64 condons there is 61 sense codons and 3 nonsense condons. The sense codons code for amino acids and nonsense codons do not.
  
  • Nonsense codons signal the end of the proteins molecule synthesis
• AUG is the start codone that initates the synthesis of the protein
• -during translation, codons of an mRNA are read sequentially and in response to each codon the appropriate amino acid is assembled into a growing chain
• the site of translation is the ribosome and Transfer (tRNA) both recognize the specific codons and transport the required amino acids.
• each tRNA molecule has an anticodon, a sequence if three bases that is complementary to a codon.