unit 11 part 2

Question 1

rna splicing

Answer 1

• removes introns
• creates a continuous molecule with readable coding sequence
• carried out by the spliceosome

Question 2

Spliceosome

Answer 2

• A variety of proteins and several small RNAs that recognize the splice sites
• The RNAs of the spliceosome also catalyze the splicing reaction
• Functions as a ribozyme (RNA enzyme)

Question 3

• Ribozymes:

Answer 3

• catalytic rna molecule that functions as enzyme and splice rna
• not all biological catalysts are proteins

Question 3

• Three properties of RNA enable itt o function as an enzyme:

Answer 3

• can form 3d structure becuase of its abilit to base-pair with itself
• some bases in rna contain functional groups that may participate in catalysis
• rna may hydrogen bond with other nucleic acid molecules

Question 3

Some introns contain sequences that

Answer 3

mya regualte gene expression

Question 4

alternative splicing

Answer 4

• Some genes can encode for more than one polypeptide, depending on which exons get included during splicing:

Question 5

Splicing Results

Answer 5

• Proteins often have a modular architecture consisting of discrete regions called domains
• In many cases, different exons code for the different domains in a protein
• Exon shuffling may result in the evolution of new proteins

Question 6

Understanding Translation

Answer 6

• Genetic information flows from mRNA to protein through the process of translation
• Translation creates a polypeptide from the mRNA information

Question 7

transfer RNA (tRNA)

Answer 7

• tRNAs transfer amino acids to the growing polypeptide in a ribosome

Question 8

• Each tRNA molecule enables translation of a specific mRNA codon into a certain amino acid

Answer 8

• Each carries a specific amino acid on one end
• Each has an anticodon on the other end
• Anticodon base-pairs with a complementary codon on mRNA

Question 9

3D Structure of tRNA

Answer 9

• Single RNA strand that is~80 nt long
• Flattened into one plane to reveal tRNA base pairing, looks like a cloverleaf
• Hydrogen bonding twists tRNA into 3D molecule
• tRNA is roughly L-shaped with the 5’and3’ ends both located near one end of the structure
• The protruding 3’ end acts as an attachment site for an amino acid

Question 10

Ribosomes

Answer 10

• Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
• The two ribosomal subunits (large and small):
• Made of proteins and ribosomal RNA (rRNA)

Question 11

A site

Answer 11

holds the tRNA that carriers the next amino acid to be added to the chain

Question 12

P site

Answer 12

holds the tRNA that carriers the growing polypeptide chain

Question 13

E site

Answer 13

is the exit site where discharged tRNA leave the ribosome

Question 14

• The three stages of translation:

Answer 14

• Initiation
• Elongation
• Termination
• Energy is required for some steps

Question 15

Synthesizing a polypeptide - Initiation

Answer 15

• The start codon (AUG) signals the start of translation
• A small ribosomal subunit binds with mRNA and a special initiator tRNA
• The small subunit moves along the mRNA until it reaches the start codon (Met)
• Proteins called initiation factors bring in the large subunit that completes the translation initiation complex

Question 16

Synthesizing a polypeptide - Elongation

Answer 16

• During elongation, amino acids are added one by one to the C-terminus of the growing chain
• Each addition involves proteins called elongation factors
• Translation proceeds along the mRNA in a 5′ → 3′ direction
• The ribosome and mRNA move relative to each other, codon by codon

Question 17

• Elongation occurs in three steps

Answer 17

codon recognition, peptide bond formation, and translocation
* Requires energy during the first and third steps

Question 18

Synthesizing a polypeptide - Termination

Answer 18

• Elongation continues until a stop codon in the mRNA reaches the A site of the ribosome
• The A site accepts a protein called a release factor

Question 19

Release factor

Answer 19

causes the addition of a water
molecule instead of an amino acid
* Hydrolysis, splits bond between tRNA and polypeptide
- energy is required

Question 20

translation folding protein does what

Answer 20

• During translation, polypeptide chain spontaneously folds into 3D molecule
• A gene determines primary structure, and primary structure in turn determines shape
• Often translation is not sufficient to make a functional protein

Question 21

Post Translational Modifications

Answer 21

• Polypeptide chains are modified after translation or targeted to specific sites in the cell
• Post-translational modifications may be required before the protein can begin doing its particular job in the cell
• Examples: protein cleavage, phosphorylation, acetylation

Question 22

Ribosomes
- Ribosomes are identical and can switch from free to bound

Answer 22

• free ribosomes (cytosol)
• Free ribosomes mostly synthesize proteins that function in the cytosol
• bound ribosomes (attached to ER)
• Bound ribosomes make proteins of the endomembrane system and proteins that are secreted from the cell

Question 22

• Polypeptide synthesis always begins in the

Answer 22

cytosol
- synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER

Question 23

Polypeptides destined for the ER or for secretion are marked by a

Answer 23

signal peptide

Question 24

• A signal-recognition particle (SRP)

Answer 24

Binds to the singal peptide on the N terminus
* The SRP escorts the ribosome to a receptor protein built into the ER membrane
* Polypeptide synthesis resumes, sending polypeptide into ER lumen

Question 25

• Polyribosome (or polysome):

Answer 25

• Multiple ribosomes can translate a
  single mRNA simultaneously
• Polyribosomes enable a cell to make many copies of a polypeptide very quickly

Question 26

Bacterial Processes

Answer 26

• A bacterial cell ensures a streamlined process by coupling transcription and translation
• Occuratsametime
• In this case the newly made protein can quickly diffuse to its site of function

Question 27

Mutations

Answer 27

• Mutations are changes in the genetic information of a cell
• Mutations of one or a few nucleotides can affect protein structure and function
• If a mutation has an adverse effect on the phenotype of the organism
• Referred to as a genetic disorder or hereditary disease

Question 28

Spontaneous mutations can occur during errors in

Answer 28

DNA replication, recombination, or repair
* Mutagens are physical or chemical agents that can cause mutations

Question 29

• Point mutations:

Answer 29

changes in just one nucleotide pair of a gene
* The change of a single nucleotide in a DNA template strand can lead to the production of an abnormal protein
* Point mutations within a gene can be divided into two general categories:
* Single nucleotide-pair substitutions
* Nucleotide-pair insertions or deletions

Question 30

• Point mutations:

Answer 30

changes in just one nucleotide pair of a gene
* The change of a single nucleotide in a DNA template strand can lead to the production of an abnormal protein
* Point mutations within a gene can be divided into two general categories:
* Single nucleotide-pair substitutions
* Nucleotide-pair insertions or deletions

Question 31

• Silent mutations:

Answer 31

• No effect on the amino acid produced by a codon because of redundancy in the genetic code
• Due to Wobble

Question 32

• Missense mutations:

Answer 32

• Still code for an amino acid, but not the correct amino acid

Question 33

• Nonsense mutations:

Answer 33

• Change an amino acid codon into
  a stop codon
• Most lead to a nonfunctional protein

Question 33

• Insertion or deletion (in/del)

Answer 33

of nucleotides often alters the reading frame, producing a frameshift mutation
* Depends if in/del is a multiple of three

• These mutations may have a disastrous effect on the resulting protein