From Gene to Protein

Question 1

DNA Sequence

Transcription

Answer 1

DNA sequence of a gene is copied to make an RNA molecule

One of the two DNA strands, the template strand, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript

Question 2

DNA Sequence

Translation

Answer 2

sequence of the mRNA is decoded to specify the amino acid sequence of a polypeptide

Question 3

Codons

Answer 3

The nucleotides of the mRNA are read in triplets (groups of three) called codons

Question 4

Codon Count:

Answer 4

There are 61 codons that specify/encode amino acids and only 20 different amino acids, so the genetic code is redundant

Question 5

Reading Frame

Answer 5

way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets

it’s a codon chart.

Question 6

RNA Synthesis catalyzed by:

Answer 6

RNA polymerase

The DNA sequence where RNA polymerase attaches is called the promoter

Question 7

Transcription

What is the RNA strand complementary to?

Answer 7

The RNA is complementary to the DNA template strand

Question 8

Transcription Unit

Answer 8

The stretch of DNA that is transcribed

Question 9

RNA Processing

Answer 9

Enzymes in the eukaryotic nucleus modify pre-mRNA (RNA processing) before the genetic messages are dispatched to the cytoplasm

Question 10

Introns

Answer 10

Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that lie between coding regions = introns

These are removed through RNA splicing

Question 11

Exons

Answer 11

a segment of a DNA or RNA molecule containing information coding for a protein or peptide sequence.

The other regions are called exons because they are eventually expressed, usually translated into amino acid sequences

Question 12

Messenger RNA (mRNA)

Answer 12

Genetic information flows from mRNA to protein through the process of translation

Genetic information flows from mRNA to protein through the process of translation

Question 13

Transfer RNA (tRNA)

Answer 13

tRNAs transfer amino acids to the growing polypeptide in a ribosome

• Genetic information flows from mRNA to protein through the process of translation
• Each tRNA molecule enables translation of a given mRNA codon into a certain amino acid
• Each carries a specific amino acid on one end
• Each has an anticodon on the other end; the anticodon base-pairs with a complementary codon on mRNA

Question 14

Ribosome

Answer 14

• perform biological protein synthesis
• link amino acids together in the order specified by the codons of mRNA molecules to form polypeptide chains

A ribosome has 3 binding sites for
tRNA:
* P site holds the tRNA that carries the growing polypeptide chain
* A site holds the tRNA that carries the next amino acid to be added to the chain
* E site is the exit site, where discharged tRNAs leave the ribosome

Question 15

When are polypeptide chains modified?

Answer 15

Polypeptide chains are modified after translation or targeted to specific sites in the cell

Question 16

Protein Folding

Answer 16

During synthesis, a polypeptide chain begins to coil and fold spontaneously into a specific shape: a three-dimensional molecule with secondary and tertiary structure

A gene determines the primary structure, and the
primary structure in turn determines shape

Question 17

Where does polypeptide synthesis begin?

Answer 17

Polypeptide synthesis always begins in
cytosol

Question 18

Cytosol

Cytosol

Answer 18

the aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended

Question 19

Signal Peptide

Answer 19

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

Question 20

Signal-Recognition Particle (SRP)

Answer 20

A signal-recognition particle (SRP) binds to the signal peptide

SRP escorts the ribosome to a receptor protein built into the ER membrane

Question 21

Silent Mutations

Answer 21

Have no effect on amino acid produced by a codon because of redundancy in the genetic code

Question 22

Missense Mutations

Answer 22

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

Question 23

Nonsense Mutations

Answer 23

Change an amino acid codon into a stop codon