translation

Question 1

what is translation?

Answer 1

RNA -> protein, translating message into a final product: protein or polypeptide chain

Question 2

what is the difference between polypeptide chain and protein?

Answer 2

some proteins are comprised of more than one polypeptide chain

Question 3

what does the end product of translation represent?

Answer 3

the nucleotide sequence present in the gene of interest

Question 4

what is special about the DNA sequence?

Answer 4

they occur in triplets that yield complementary triplets of nucleotides in the mRNA

Question 5

what are each of the nucleotide triplets in mRNA known as?

Answer 5

codons

Question 6

what is the genetic code?

Answer 6

all of the codons and the amino acids they code for

Question 7

what are the two regions of tRNA that are special?

Answer 7

1. anticodon that binds to a specific codon in mRNA
2. carries amino acid that corresponds to the codon

Question 8

how does tRNA appear in the cell with its specific amino acid attached?

Answer 8

tRNA ligase: by a family of 20 tRNA synthetase enzymes

Question 9

true or false: each tRNA synthetase enzyme recognizes one and only one amino acid and attaches it to its appropriate tRNA

Answer 9

true

Question 10

what happens when the enzyme has bound both serine and its tRNA?

Answer 10

charging/loading tRNA: the enzyme then uses the energy in ATP to create a bond between serine and the tRNA

Question 11

what is the purpose of rRNA?

Answer 11

combines with other proteins to form a ribosome

Question 12

what is the purpose of the ribosome?

Answer 12

provides the scaffolding needed to combine the appropriate amino acids in the right sequence to form the protein being synthesized.

Question 13

what are the two subunits of the ribosome?

Answer 13

50S and 30S

Question 14

what is the key step in the translation process of eukaryotic cells that involve 30S subunit, mRNA and a specific initiator tRNA carrying methionine?

Answer 14

the 30 S subunit moves along the mRNA until it locates and binds to the ‘start codon’, AUG. At this point, the two subunits come together creating a passageway through which the mRNA that is to be translated moves.

Question 15

what is the combination of the two ribosomal subunits, the strand of mRNA, and the initiator tRNA comprise known as?

Answer 15

the ‘translation initiation complex’

Question 16

describe the passageway of the ribosome through which tRNAs move and their anticodons bind to the codons on the mRNA via A,E, and P site

Answer 16

the first tRNA that helped initiate the process, has already bound to the start codon on the mRNA. This tRNA sits in what is known as the ‘P site’ within this passageway. Based on the second codon, the tRNA with the appropriate anticodon and amino acid enters the passageway. This tRNA then binds to the mRNA in the region of the ribosome called the ‘A site’ When this happens, an enzymatic component of the ribosome links the methionine on the first tRNA to the amino acid carried in by the second tRNA. This occurs at the region of the ribosome called the ‘P site’ and the two amino acids are linked with a peptide bond. Once this happens, the ribosome shifts over one codon to allow the first tRNA to leave through the ‘ E site ’. This allows the next tRNA to bind to its codon in the A site, and the process is repeated to elongate the polypeptide one amino acid at a time. In essence, each tRNA with the appropriate anticodon carrying the appropriate amino acid enters, binds, adds its amino acid to the polypeptide and then leaves.

Question 17

what are the three stop codons?

Answer 17

UAA, UAG and UGA

Question 18

true or false: tRNA recognizes the stop codons

Answer 18

false

Question 19

how does the process stop?

Answer 19

release factor enters A site, then an enzymatic reaction occurs that separates the tRNA in the P site from the polypeptide chain. As a result, synthesis of the polypeptide is terminated and it is released through an opening in the 50S subunit.
also causes the 50S and 30S subunits to separate from the mRNA and from each other

Question 20

what causes a primary protein structure to change shape?

Answer 20

hydrogen bonds form between the amino acids

Question 21

a hydrogen bond might form between the carbonyl group of one amino acid and the amino group of another one several amino acids down the chain, what could result if it happens several times along the length of the protein? what about hydrogen bonds between other amino acids in the chain

Answer 21

alpha helix
secondary structure: beta sheet, bend or other shapes

Question 22

what bonds affect tertiary structure?

Answer 22

covalent and non-covalent interactions

Question 23

what interactions account for the 3D shape of proteins?

Answer 23

• hydrophobic portions of nonpolar amino acids orient themselves so they can avoid the aqueous environment of the cell.
• two sulfur containing amino acids (methionine, cysteine, homocysteine and taurine) in different parts of the protein might form di-sulfide bonds with each other
• positively and negatively charged side groups of amino acids could form ionic bonds.

Question 24

what is the quaternary structure?

Answer 24

several highly folded proteins are assembled together as subunits that carry out complex functions

Question 25

what are examples of quaternary structure?

Answer 25

hemoglobin proteins in red blood cells and ion channel proteins that transport specific ions across cell membranes

Question 26

what is the purpose of hemoglobin?

Answer 26

pick up oxygen in your lungs and release it where it is needed in your tissues.

Question 27

describe the process of how a hemoglobin is made

Answer 27

1. nucleotides transcribed by RNA polymerase into mRNA that leaves the nucleus where it interacts with a ribosome 2. codons in the mRNA are recognized by the anticodons in the tRNA molecules that carry the appropriate amino acids to the ribosome where they are linked by peptide bonds 3. hemoglobin protein that then folds on itself in a precise fashion and forms a quaternary structure with 3 other similarly folded hemoglobin proteins

Question 28

what would happen if one of the DNA bases in the hemoglobin sequence was changed?

Answer 28

change results in a different amino acid being incorporated into the hemoglobin protein. ex. thymine replaces an adenine in the DNA sequence. How would this cause problems? Well, it changes the sixth codon from GAG to GTG, which means that rather than having a tRNA carrying glutamic acid enter the picture, it’s replaced by one carrying valine.

Question 29

how does the one nucleotide change affect the hemoglobin?

Answer 29

sickle cell anemia: It causes hemoglobin molecules after they’ve released their oxygen molecules in the tissues to stick together and form long fibers. These fibers change those red blood cells from their normal bi-concave disc shape to that resembling a sickle