Advanced A&P - Unit 1a: DNA & Protein Synthesis

DNA

A&T, C&G, found primarily in nucleus, deoxyribose sugar, double stranded, contain the genetic info need to synthesize protein, & has the ability to replicate itself

RNA

A&U, C&G, found primarily in cytoplasm, ribose sugar, single stranded, 3 different types

mRNA (messenger RNA)

carries transcribed DNA info to cytoplasm and acts as a template for protein synthesis

rRNA (ribosomal RNA)

part of the structure of a ribosome

tRNA (transfer RNA)

carries amino acids to mRNA

DNA replication

occurs during interphase of the cell cycle in preparation for mitosis; the process of copying the information encoded in DNA to produce RNA

DNA replication process

1. during interphase, hydrogen bonds between base pairs are broken.

2. double helix unwinds, strands separate; bases are exposed.

3. DNA polymerase gathers free nucleotides containing complementary bases and binds them to exposed bases on original DNA strands.

4. Other enzymes bind together the sugar-phosphate backbone molecules in the new nucleotide to form new DNA strands.

5. Each original DNA strand has a new complementary strand.

DNA polymerase

catalyzes complementary base pairing by gathering free nucleotides with complementary bases, and binds them to the exposed bases on original DNA strands

protein synthesis

transcription and translation

transcription

occurs in nucleus, process of copying DNA info into an RNA sequence (mRNA)

steps of transcription

1. RNA polymerase binds to the gene’s promoter.

2. A section of the DNA unwinds and pulls apart, exposing part of the base sequence.

3. RNA polymerase moves along the DNA strand, adding complementary nucleotides to a growing mRNA chain.

4. RNA polymerase reaches the termination signal, releases the new mRNA, and leaves the DNA.

5. The DNA helix rewinds into its double-helix shape.

(6.) mRNA passes through pore in nuclear envelope and enters into cytoplasm.

RNA polymerase

assemble nucleotides into RNA

codon

set of 3 contiguous nucleotides of a mRNA molecule that specifies a particular amino acid

anticodon

3 contiguous nucleotides of a tRNA that are complementary to a specific mRNA molecule)

translation

occurs in cytoplams, mRNA is translated from the “language” of nucleic acids to the “language” of amino acids

steps of translation

1. a ribosome binds to the mRNA near the start codon.

2. a tNRA molecule with a complementary anticodon binds to the mRNA codon, bringing its amino acid to the ribosome.

3. a second tRNA brings the next amino acid to the ribosome.

4. a peptide bond is formed between the two amino acids and the first tRNA is released.

5. the process of tRNA binding and peptide bond formation repeats for each codon in the mRNA sequence as the ribosome moves along its chain.

stop codons

do not have corresponding tRNA anticodons

mutation

errors that produce changes in the DNA sequence

spontaneous mutation

arises from chemical tendency of free nitrogenous bases to exist in slightly different structures, an unstable base, or existing (parental) DNA strand slips, adding to or deleting nucleotides from the sequence

induced mutation

a response to exposure to certain chemicals or radiation (called mutagens)

protection against mutation

• DNA repair

• 64 possible codons and 30 different types of amino acids; therefore, more than one codon can code for a particular amino acid

• if a mutation alters a base in the second position, the substituted amino acid is often similar in overall shape to the correct one, and protein is not changed enough to effect the function

  • a person has two copies of each chromosome and therefore, of each gene; if one copy is mutated, the other may provide enough of the genes normal function to maintain health

DNA repair

specialized “repair enzymes” recognize and remove mismatched nucleotides and fill resulting gap with the accurate, complementary nucleotide

gene

DNA sequence containing the information used to make a particular polypeptide/protein