2.7 DNA Replication, Transcription And Translation

Question 1

What is the function of helicase?

Answer 1

Unwinds and separates the DNA double helix. Breaks h bonds.

Question 2

What are SSBs?

Answer 2

Single stranded binding proteins stabilize the newly single stranded regions

Question 3

What is the function of DNA Gyrase?

Answer 3

Used to stop the double stranded areas outside the replication fork from supercoiling.

Question 4

What is the function of RNA primase?

Answer 4

Adds a short length of RNA primer to the template strand of DNA to allow DNA polymerase to bind and begin replication

Question 5

What is DNA polymerase III?

Answer 5

Adds nucleotides in a 5’ to 3’ direction.

Question 6

What is a leading strand?

Answer 6

Polymerase III can add continuously in a 5’ to 3’ direction (same direction as replication fork)

Question 7

What is a lagging strand?

Answer 7

Polymerase III must move away from the fork and replicate DNA in small chunks (Okazaki fragments)

Question 8

What is the function of DNA polymerase I?

Answer 8

Removes RNA primers and replaces them with DNA. Corrects error in DNA bases.

Question 9

What is the function of DNA ligase?

Answer 9

Seals up the bases to make new strands (connects Okazaki fragments).

Question 10

How does DNA replication differ in euk and prok cells?

Answer 10

Initiated at many points in euk cells. In prok starts at one end and continues until finished.

Question 11

What is protein synthesis?

Answer 11

The making of proteins. Occurs in 2 stages: transcription and translation.

Question 12

What is transcription?

Answer 12

Copying of a portion of DNA containing the information for making the needed protein into RNA. RNA copy carries DNA message to ribosome where protein will be built.

Question 13

What is translation?

Answer 13

Reading of RNA message and translation from nucleotide language to amino acid language at the ribosome

Question 14

What is the purpose of RNA polymerase?

Answer 14

Binds to a site on the DNA at start of a gene. Moves along gene to separate DNA

Question 15

What is the antisense strand?

Answer 15

Strand of DNA used in transcription. Only this strand is copied.

Question 16

What is the RNA called that is copied from the DNA?

Answer 16

Messenger RNA (mRNA)

Question 17

What is a promoter region?

Answer 17

Region of DNA located “upstream” of a gene that allows RNA polymerase to recognize the gene that needs to be transcribed. Tends to be repetitive ATAT

Question 18

What is a terminator?

Answer 18

Region of DNA that tells RNA polymerase to stop transcription. When terminator is reached, mRNA peels off of DNA template and DNA reforms h bonds.

Question 19

What is a codon?

Answer 19

Sequences of mRNA nucleotides grouped into triplets.

Question 20

What are the functions of non-coding DNA?

Answer 20

Regulators of gene expression (operator in lac operon), introns (chopped out of mRNA), telomeres (ends of chromosomes), and genes for tRNA. Some DNA sequences produce polypeptides, tRNA, rRNA, and regulate gene expression (lac operon).

Question 21

What happens when euk cells modify mRNA?

Answer 21

Introns are removed from mRNA and are not translated. Exons are kept and spliced together to form mature mRNA

Question 22

How does the environment of a cell impact gene expression?

Answer 22

Some proteins required at all times and are expressed continuously. Others only need to be produced at certain times in certain amounts so production is regulated (lac operon for lactose in prok cells)

Question 23

How does the lac operon in E.coli work to express the genes responsible for the absorption of lactose when required?

Answer 23

In the presence of lactose, a repressor gene is deactivated and does not bind to the operator. In absence of lactose, repressor protein is activated and binds to the operator to save energy instead of creating enzymes to process lactose.

Question 24

What is needed for translation?

Answer 24

mRNA, ribosome, and tRNA

Question 25

What is a ribosome?

Answer 25

Ribosomes are made of proteins and rRNA. They have a large and small subunit. 3 binding sites for tRNA mocs, 2 at any time fit. E, P, and A sites. Binding site for mRNA.

Question 26

What are the two types of ribosome?

Answer 26

Free ribosomes: in cytoplasm, synthesize proteins for use in cell. Bound ribosomes: attached to ER, synthesize proteins for secretion from cell or for lysosomes

Question 27

What are the features of tRNA?

Answer 27

Sections that become double stranded by base pairing (loops), triplet of bases called anticodon

Question 28

How are tRNA molecules activated?

Answer 28

Recognized by tRNA activating enzyme that attaches specific amino acid to tRNA. Each enzyme is specific to one of the 20aas and the correct tRNA moc. Active site of the enzyme specific to correct aa and correct tRNA

Question 29

What are the steps in translation?

Answer 29

1. Initiation 2. Elongation and translocation 3. Termination

Question 30

What is initiation?

Answer 30

mRNA moc binds to small subunit of ribosome at binding site. Initiator tRNA (methionine), binds to start codon (AUG). Large subunit of ribosome binds to small one. Initiator tRNA is in P site. Next codon signals another tRNA to bind at A site. Peptide bond formed between aas.

Question 31

What is elongation and translocation?

Answer 31

The continuation of the aa building process and movement of the mRNA through the ribosome. Ribosome translocates 3 bases along mRNA, moving tRNA to E site and allowing new tRNA to bond w mRNA in A site.

Question 32

What is termination?

Answer 32

The ribosome reaches a stop codon (no tRNA has anticodon), polypeptide is released, ribosome mRNA and tRNA fall apart, polypeptide chain folds into a shape based on the aa's it has.

Question 33

What is a group of ribosomes moving along the same mRNA?

Answer 33

Polysome

Question 34

What is PCR?

Answer 34

Polymerase chain reaction

Question 35

How does PCR work?

Answer 35

Heat used to separate DNA. Cooling to attach DNA primers. Taq polymerase (does not denature at high temperatures) used to build new DNA (5' to 3'). Heat separates strands and cycle begins again.

Question 36

What is satellite DNA?

Answer 36

Repetitive sequences of non coding DNA. (Telomeres)

Question 37

How did human insulin become commercially available?

Answer 37

Genetically modified E.coli. Gene from healthy human pancreas cell transferred to host cell DNA. Gene transcribed and translated into insulin that is harvested in large quantities. Works because DNA has universal genetic code.

Question 38

What did Meselson and Stahl prove?

Answer 38

The replication of DNA is semiconservative