Chapter 10

Question 1

structures of DNA vs. RNA

Answer 1

• DNA
- double helix
- nucleotides: ACTG
• RNA
- single strand
- uses the sugar ribose 
- nucteotides: ACUG

Question 2

DNA replication

Answer 2

• follows a semiconservative model
- two DNA strands separate
- each strand is used as a pattern to produce a complementary strand, using specific base pairs
- has an old strand and new strand
• proceeds in two directions at many sites simultaneously
• 3 key proteins:
- helicase: unwinds the parent DNA strand
- polymerase: adds nucleotides to a growing chain; proofreads and corrects improper base pairings
- ligase: joins small fragments into a continuous chain
-poly and lig. also repair DNA damaged by harmful radiation & toxic chemicals
• ensures that all the somatic cells in a multicellular organism carry the same genetic info

Question 3

transcription & translation

Answer 3

• the molecular chain of command is from
- DNA in the nucleus to RNA
- RNA in the cytoplasm to protein
• transcription: the synthesis of RNA under the direction of DNA
• translation: synthesis of proteins under the direction of RNA

Question 4

transcription

Answer 4

• RNA molecule is transcribed from a DNA template
• RNA nucleotides are liked by transcription enzyme RNA polymerase
- initiation: begins as RNApoly attaches to promoter
-elongation: RNA grows longer
-termination: RNApoly reaches a sequence of bases in DNA template called terminator, which signals the end of the gene
-polymerase detaches from RNA molecule and gene

Question 5

mRNA

Answer 5

• encodes amino acid sequences
• Euk. mRNA
- introns: interrupting sequences that separate
- exons: the coding regions

Question 6

tRNA

Answer 6

• function as a language converter
- converting genetic message of mRNA into the language or proteins
• performed by…
- picking up appropriate amino acid
- using special triplet of bases, called an anticodon, to recognize the appropriate codons in the mRNA

Question 7

ribosomes

Answer 7

• translation occurs on the surface of the ribosome
• coordinate functioning of mRNA and tRNA, and the synthesis of polypeptides
• have 2 subunits: small & large
- each is composed of ribosomal rRNA’s & proteins
- come together during translation
• have binding sites for mRNA and tRNAs

Question 8

codons translated into amino acids

Answer 8

• info from gene to protein is based on a triplet code
• each amino acid is specified by a codon
- 64 codons possible; 61 respond to amino acids
- some amino acids have more than one possible codon
- AUG signals start of translation
- 3 stop codons signal end of translation: UAA, UAG, & UGA

Question 9

mutation

Answer 9

• any change in nucleotide sequence of DNA
• can involve large chromosomal regions or a single nucleotide pair
• can be caused by:
- spontaneous errors that occur during DNA replication or recombination
-mutagens: high-energy radiation (ex: x-rays, UV light, or chemicals)

Question 10

point mutations (PM)

Answer 10

• base substitutions: involve the replacement of 1 nucleotide w/ another
- silent PM: has no affect at all
- missense PM: change the amino acid coding, which produces a different amino acid
- nonsense PM: change an amino acid into a stop codon
• frameshift mutations can occur from deletions or insertions
- may alter the reading frame of mRNA (grouped differently)
-may produce a nonfunctional polypeptide