CHAPTER 10

Question 1

Review from chapter 3 about nucleic acid

Answer 1

-Nucleic acids → DNA, RNA
-Found in nucleus
-Monomer : nucleotide
-Sugar, phosphate group (Backbone)
-Nitrogenous base
-Linked together by covalent bonds (strong)

Question 2

Differences between DNA and RNA

Answer 2

DNA
-Structure : double helix (spiraled)
-Sugars : deoxyribose (one less oxygen) → rigid structure, good and solid
-Bases: adenosine (A), cytosine (C), guanine (G), thymine (T)

RNA
-Structure: single stranded
-Sugars : ribose (one more oxygen) → flexible
-Bases: adenosine (A), cytosine (C), guanine (G), Uracil (U)

Question 3

Know the names and roles of the 3 main scientists who deduced the structure of DNA.

Answer 3

1. Rosalind Franklin
2. James Watson
3. Francis Crick

Question 4

Rosalind Franklin (british) role

Answer 4

-used x-ray crystallography
-She concluded that the sugar phosphate backbone is on the outside of the molecules
-Sadly wasn’t given credit at the time

Question 5

James Watson (US) & Francis Crick (british) role

Answer 5

-James got a sneak preview of rosalind’s unpublished photos
-Realized from using her photos that DNA must have a spiral/ helix shape
-Also there must be specific base pairings to keep a uniform width (T always pairs with A, C always pairs with G)
-Always paired by weak hydrogen bonds So they can come apart easily (easy to unzip)
-Realized with DNA replication, DNA replicates by a template (mold) mechanism → unzips the DNA strand and it builds 2 new complementary copies

Question 6

Describe DNA replication

Answer 6

DNA replicates by a template (mold) mechanism which unzips + builds 2 new complementary copies
- requires enzymes = DNA polymerase

Question 7

Know the 3 functions of DNA polymerases.

Answer 7

-Make covalent bonds between these new nucleotides (strands)
-Repair damaged DNA (EX: X-rays, UV rays, toxins)
-They proofread → and remove mismatched pairs (Ofc not all mistakes are caught
Which leads to mutations)

Question 8

Describe the flow of genetic info from DNA to RNA to protein

Answer 8

DNA(genotype) —transcription(happens in the nucleus)→ mRNA —translation (in cytoplasm)→protein(phenotype)

Question 9

Understand and describe the triplet code of bases (codons) and the genetic code

Answer 9

• there are 4 genetic code bases in triplets having 64 possible code words (61 of them code for Amino Acids, 1 has a dual function)
  1. codes for A.A. = met
  2. “start” codon => “AUG”
  3 others = stop codon
• 4 genetic codes:
  A, T, C, G in DNA -> nitrogenous bases
• the genetic code is universal for all life on earth

Question 10

DNA codon sequence:
CGA TGG CAT ACG CAG

Find the corresponding mRNA codon, tRNA anticodon, and amino acid attached to it.

Answer 10

mRNA:
GCU ACC GUA UGC GUC
tRNA:
CGA UGG CAU ACG CAG
amino acid:
Ala Thr Val Cys Val

Question 11

Describe transcription. Know the 3 phases of each process

Answer 11

• requires enzyme = RNA polymerase
  -> unzips 2 DNA strands
  -> links new RNA nucleotide (= monomer)

3 PHASES:
1. Initiation
- *RNA polymerase attaches to promoter DNA
-> DNA strand = template strand
2. mRNA Elongation
- double helix reforms afterward
3. Termination
- RNA polymerase reaches the terminator DNA
*RNA must be modified before it can leave nucleus -> gets a “cap + tail” to give it proper I.D. being able to be recognized by ribosome

Question 12

Describe translation. Know the 3 phases of each process and all the “players”
involved (organelles, enzymes, location in cell, where to stop and start, figs. 10.13 – 10.20).

Answer 12

“players” Required:
-> mRNA
-> transfer RNA (tRNA) - acts as a “translator” + brings in the correct A.A. one tRNA for each specific A.A.
tRNA Structure:
- one end has a triplet anticodon
- opposite end has an A.A. attachment site
Ribosome:
2 subunits:
-> larger one - binding site for tRNA’s
-> smaller one - binding site for mRNA
*acts like a clamp/vice to hold tRNA + mRNA together

3 PHASES:
1. Initiation (on the mRNA)
- “First” tRNA binds to the “start” codon (on mRNA)
-> A.A. = Met (Methionine)
-> anticodon on tRNA = UAC
2. Elongation of Amino Acid chain = polypeptide chain
- A.A.’s joined by peptide bonds
3. Termination at the “stop” codon
- stop codon: UAC

Question 13

Define genome.

Answer 13

An organism’s complete set of DNA

Question 14

What is the human genome project?

Answer 14

1985 - 2003
- discovering that there is only a 2% difference between human + chimp

Question 15

What are point mutations?

Answer 15

single base change in DNA

Question 16

What is the effect of base substitutions?

Answer 16

• replace/swap one base (A, C, T, G)
  A) Some are not a problem
  ex: silent mutation => has no effect
  Why? “New” codon codes for same A.A.
  B) Some are harmful
  ex: sickle cell disease -> A.A. #6 is wrong

Question 17

What is the effect of base insertions/deletions?

Answer 17

• add or remove one base
  -> almost always harmful
  Why?
  Changes the reading frame -> changes the A.A. chain -> protein is “wrong”

Question 18

What are mutagens? Give examples.

Answer 18

causing mutations
ex: X-rays, U.V. Rays, toxic chemicals (also spontaneous mutations)
- not all mutations are bad because they cause genetic variety/natural selection