Clicker Review

Question 1

Let’s follow a triplet of DNA nucleotides.

The TEMPLATE strand of DNA: 3’ C T A 5’

What is the NON-TEMPLATE DNA sequence?

Answer 1

5’ G A T 3’

Question 2

Let’s follow a triplet of DNA nucleotides.

The TEMPLATE strand of DNA: 3’ C T A 5’

What is the mRNA codon sequence?

Answer 2

5’ G A U 3’

Question 3

Let’s follow a triplet of DNA nucleotides.

The TEMPLATE strand of DNA: 3’ C T A 5’

What is the ANTICODON sequence?

Answer 3

3’ C U A 5’

Question 4

Let’s follow a single triplet of DNA nucleotides.

The TEMPLATE strand of DNA: 3’ C T A 5’

Answer 4

3’ C T A 5’ DNA Template

5’ G A T 3’DNA Non-template

5’ G A U 3’mRNA codon

3’ C U A 5’anticodon

Question 5

The most important part of DNA’s structure, that allows it to easily make copies of itself is:

Answer 5

The base pair rules of A=T and C=G

Without Chargaff’s Rules, even with two strands, one strand of DNA as a template would not have any reliable guide to the order of bases on the other strand.

Question 6

The accepted model of DNA replication used today is the:

Answer 6

Semi-conservative method

In this method, the new strands of DNA are each made of one strand of “old” DNA and one strand of “new” DNA nucleotides.

Question 7

New DNA nucleotides are added to the _______ of the growing daughter strand.

Answer 7

3’ end

Therefore, the new strand grows in the 5’ to 3’ direction.

Question 8

The role of single stranded binding proteins in DNA replication is to

Answer 8

Keep the 2 strands apart during DNA replication

Question 9

The role of single stranded binding proteins in DNA replication is to

Answer 9

Add DNA nucleotides to the growing strand.
DNA polymerase

Untwist the DNA double helix and separate the strands.
Helicase

Keep the 2 strands apart during DNA replication
Single strand binding proteins

Keep the DNA strand from overwinding ahead of replication: Topoisomerase

Seal Okasaki fragments together: DNA Ligase

Question 10

Other Enzyme Helpers

Answer 10

Nuclease: Cuts segments of DNA for repair

Primase: Makes RNA primer which begins DNA replication

Telomerase: Extends telomere segments in germ line cells to prevent chromosomes from shortening during DNA replication in gametes

Question 11

The region of chromosomes where DNA is less tightly condensed so gene expression can take place is the __________.

Answer 11

Euchromatin

DNA in these regions is less tightly wound around the histone proteins. Heterochromatin is much more condensed and can be found in the telomere and centromere regions where little to no gene expression occurs.

Question 12

Which type of RNA has an anticodon?

Answer 12

tRNA

Question 13

The site on the ribosome that docks the tRNA that is empty and ready to go get a another amino acid is the ________.

Answer 13

E site

Question 14

Which of the following is not DIRECTLY used during translation?

Answer 14

RNA polymerase

RNA polymerase plays its role during transcription of DNA nucleotides into RNA nucleotides to make mRNA.

Question 15

True or False: Inducible operons use inducers and not repressors.

Answer 15

False

Inducible operons will use BOTH inducers and repressors. Repressors will block RNA polymerase from binding unless an inducer makes the repressor inactive. In the lac operon, the inducer allolactose binds with the repressor so that transcription can occur.

Question 16

Which of the following in NOT a way eukaryotes control gene expression?

• Degradation of mRNA
• Chromatin modification
• RNA processing
• Operons
• Post translation protein modification

Answer 16

Operons

The operon model of gene expression control is in prokaryotes, not eukaryotes.

Question 17

If there is no glucose and plenty of lactose in the environment, you would expect the lac operon to be

Answer 17

On and transcribing lacZ, lacY & lacA

E. coli would need the genes of the lac operon to be transcribed in order to import and break down lactose properly so we would expect the operon to be on if lactose is present (by way of allolactose acting as an inducer which blocks the repressor).

Question 18

Which of the following genes codes for b-galactosidase, the enzyme that breaks down lactose into glucose and galactose?

Answer 18

lacZ: b-galactosidase
lacA: transacetylase
lacY permease
lacI: regulatory gene = repressor

Question 19

Over an organism’s lifetime, is it possible for them to acquire traits that are then passed on to their offspring?

Answer 19

Yes! Sort of.

While the actual genes (DNA sequences) and what traits they encode are what is traditionally thought of as “inherited”, it turns out the control of those genes can be altered throughout an organism’s lifetime AND those control changes can be passed on to offspring.

Question 20

An anabolic pathway is one that ______.

Answer 20

builds bigger molecules from smaller molecules = anabolic

Question 21

If an operon is described as REPRESSIBLE, it is usually _______.

Answer 21

On

The operon genes are therefore making their gene products unless something makes the repressor active and shuts the operon off (represses).

Question 22

Let’s say a mutation occurs in the regulatory gene lacI so that it can NOT make a functional repressor protein for the lac operon. What effect would you expect?

Answer 22

It won’t matter if lactose is present or not: The lac operon will be on all the time.

If the repressor is never made, it can therefore never block RNA polymerase from binding to the operator so the lac operon will stay on, lactose or not.

Question 23

What is an operon?

Answer 23

A mechanism for coordinated control of several genes involved in a biochemical pathway

A mechanism for allowing gene expression to be controlled by environmental cues

Question 24

The operon model is a method of gene expression control in _________.

Answer 24

prokaryotes only

Prokaryotes have the operon model of one operator controlling the expression of multiple genes. While eukaryotes do not have operons, they have many other mechanisms for gene expression control that prokaryotes do not such as alternative mRNA editing.

Question 25

Which of the following modifications to chromatin and DNA would INCREASE transcription?

Answer 25

Both acetylation of histones and de-methylation of DNA

Acetylation of histones will lessen the attraction between the histones and DNA which allows more transcription (looser packing). Taking DNA methyl groups away from DNA will also increase transcription.

Question 26

Which type of macromolecule is DNA?

Answer 26

Nucleic Acid

DNA and RNA are both nucleic acids.

Question 27

If there is 20% adenine in a given DNA sample, how much thymine is there?

Answer 27

20%

Amount of adenine will always match the amount of thymine since A pairs with T.

Question 28

If there is 20% adenine in a given DNA sample, how much cytosine is there?

Answer 28

30%

If there is 20% A, there is also 20% T which will take up 40% of the DNA nucleotides. If you subtract 100%-40% you get 60% left over which must be equally divided between C and G. There would be 30% G as well as 30% C.

Question 29

Where is the “code” in DNA?

Answer 29

The order of nitrogenous base pairs

In a DNA strand, the sugar is always deoxyribose and all the phosphate groups are the same so it is the order of bases that give the genetic code. We’ll see soon in Chapter 17 how that order determines how proteins are constructed.

Question 30

In the semi-conservative method of DNA replication, the ________.

Answer 30

resulting two double stranded DNA molecules are both a mixture of one strand of “old” parental DNA and one strand of “new” daughter DNA

Question 31

Do you think RNA primers can stay in the DNA strand?

Answer 31

No

The RNA nucleotides are going to have to be removed and replaced by DNA nucleotides. This is going to cause some problems at the end of linear chromosomes like the ones in eukaryotes but we’ll get back to that later.

Question 32

Which of the following is a limitation of DNA polymerase?

Answer 32

DNA polymerase can only add nucleotides to the 3’ end of the growing strand.

**DNA polymerase can not initiate the adding of DNA nucleotides so it requires a DNA primer: RNA primer, not DNA

Question 33

Can a human gene work inside bacteria?

Answer 33

Yes!

ALL organisms share a universal genetic code so human genes inserted into bacteria can be made into human proteins by the bacteria. In fact, the human insulin used by millions of diabetics is mostly manufactured by bacteria possessing the human insulin gene inserted by genetic engineering.

Question 34

What is the monomer of nucleic acids?

Answer 34

Nucleotides

Nucleic acids (DNA & RNA) are linear polymer molecules made of repeating subunits of nucleotides.

Question 35

What is the monomer of proteins?

Answer 35

Amino acids

Proteins are polypeptide strands of repeating units of amino acids. The dilemma in protein synthesis is translating the monomer of nucleic acids (nucleotides) into the monomer of proteins (amino acids).

Question 36

How many bases correspond to an amino acid?

Answer 36

3

1 base/amino acid doesn’t work since there are 20 amino acids and only 4 bases. 2 doesn’t work either since that only gives you 16 unique base pair combinations. Need 3 bases to have enough for the 20 amino acids.

Question 37

The DNA template strand for a gene sequence is:
3’ A A T 5’ (Template)
What would be the corresponding mRNA transcript?

Answer 37

5’ U U A 3’

The mRNA transcript is made of RNA nucleotides with complementary base pairs to the DNA. U will substitute where T would be for DNA. The polarity is anti-parallel to the DNA strand.

Question 38

Can a codon designate more than one amino acid?

Answer 38

No!!!!

Each of the 61 coding codons will only identify one amino acid to avoid confusion. However, a given amino acid might have more than one codon identifying it. For example, AGU and AGC both code for serine but neither would ever code for any other amino acid other than serine.

Question 39

Which of the following would be an anticodon for these 3 DNA nucleotides from a template strand of DNA?
3’ A G T 5’ (DNA template strand)

Answer 39

3’ A G U 5’

This is the anticodon which is the same sequence and polarity as the template DNA (with U substituted for T). The CODON would be 5’ UCA 3’

Question 40

Is it potentially worse to have a single base pair
deleted/inserted vs. a whole codon (3 base
pairs) inserted or deleted?

Answer 40

Single base pair