LAB EXAM Manual 1-4

Question 1

Why is bacteria a useful organism to use in studies of evolution?

Answer 1

Bacteria is a useful source to examine evolution because they have generation times as short as 20 minutes

Question 2

What did lenski say was the only factor influencing evolution?

Answer 2

Time
- he grew populations in flasks with glucose as the only sugar, a constant temp and no predators,
-he noticed some bacteria formed mutations
- eventually there was evolution from the original group of bacteria

Question 3

What is an aseptic technique?

Answer 3

When working with microoraganims you use a aseptic (sterile) technique to ensure that you do not contaminate yourself or your culture.

Question 4

How should we label our agar plates? And what direction do we pour it?

Answer 4

We have the low side arrow at an angle and we pour from high to low.
- the arrow will be pointing toward the thinnest depth of agar, which will be the region of lowest salt concentration

Question 5

The tube in class that we obtain for the agar plate formation, what is the green cap tube contain? What is the blue cap tube?WHY does the second layer on agar take longer to cool?

Answer 5

Molten 15% saline- nutrient agar : GREEN
Molten nutrient agar: BLUE
- it takes longer to cool than the first layer because of the insulating effect of the first layer

Question 6

What are the chains of DNA made up of?

Answer 6

They are made up of building blocks known as deoxyribonuclotides which have three components:
1. A five-carbon deoxyribose sugar, whose carbons are numbered from 1’-5’
2. One of four nitrogenous bases covalently bound to carbon 1’ of the deoxyribose
3. At least one Phosphate group covalently bound to carbon 5’ of the deoxyribose (their can be many as three phosphate groups)

Question 7

What are the four types of nitrogenous bases that are found in deoxyribonucleotides that make up polymers of DNA? What are adenine and guanine known as? And what are thymine and cytosine known as?

Answer 7

Adenine
Guanine
Thymine
Cytosine

A+G= PURINE
T+C= PYRIMIDINES

Question 8

How much information is actually stored in DNA?

Answer 8

In the nucleus of each of your cells, the 46 chromosomes contain 6 billion base pairs of information
- each chromosome contains two strands of DNA, each composed of 100 million nucleotide units on average
- the DNA double helix as a ladder, each step of the ladder corresponds to a nucleotide
- about 2 m of DNA in the nucleus of each of your cells

Question 9

What is the long thin DNA molecule wound around?

Answer 9

• positively charged proteins (called histones in eukaryotes) that help to fold up the DNA into a highly condensed structure called chromatin

Question 10

During Lab 2 we extracted DNA from strawberries. What was the point of the detergent and table salt?

Answer 10

• the detergent lyses the cell membranes and denatures proteins
  -the positively charged sodium ions in the table slat form favorable electrostatic interactions with the positively charged histones
• together the detergent and salt help to separate the histones from the DNA.
• DNA in the presence of sodium is highly soluble in water because water and DNA both are highly polar molecules

Question 11

To get the DNA out of the solution, what do we use during LAB 2, the one with extracting strawberry?

Answer 11

We add isopropanol to decrease the polarity of the solvent and take advantage of the incredible length of DNA by winding the DNA around itself onto a glass rod

Question 12

In Lab 2, why did we use strawberries as our source of DNA?

Answer 12

• while DNA is present in large amounts in all cells, strawberries, like many crop plants, have been bred to have multiple copies of each chromosome this is known as polyploidy.
• in most commercial strains of strawberries cells are octaploid and contain eight copies of each chromosome.
• the larger amount of DNA not only gives us more DNA to extract but actually helps the stawberries grow larger and taste better

Question 13

How can we tell that what we extracted from the cells of the stawberries was really DNA? During lab 2. HOW ARE DYES USEFUL AND WHAT SPECIFIC DYE DID WE USE?

Answer 13

• DNA does not absorb visible light appreciably, so it is colourless to the naked eye.
• however specific dyes can bind to the negatively charged phosphates and hydrophobic bases of DNA.
  -we used a fluorescent dye called SYBR Gold, that gives off a bright yellow-gold light when bound to DNA and exposed to blue light

Question 14

Why is using SYBR Gold particularly useful for detecting DNA?

Answer 14

Because it gives off fluorescent light when bound to double stranded DNA.
- the dye interacts with both the negatively charged backbone and the closely stacked bases found in the double stranded DNA.

Question 15

Why does the Dye not bind well to single stranded DNA (RNA) ?

Answer 15

Because the bases are not stacked tightly in this form of DNA.

Question 16

What does sodium hydroxide do when used to denature DNA ?

Answer 16

Sodium hydroxide is a strong base that removes some of the protons in the nitrogenous bases of DNA, thus disrupting the hydrogen bonding needed to stabilize the structure of double-stranded DNA.

Question 17

Define mutations?

Answer 17

Mutations are permanent changes to the genetic information of a cell and generally occur at a fairly low rate in most organisms.

Question 18

Mutations occur by many different mechanisms one of which is exposure of cells to ionizing radiation, such as ultraviolet light from the sun, what does radiation do to molecules?

Answer 18

These forms of radiation can ionize water molecules to form free radicals, which in turn react with nitrogenous bases of DNA to change their chemical structure, altering their ability to form specific base pairs with other bases

Question 19

Why is high amounts of radiation bad for us?

Answer 19

high amounts of radiation exposure generate more free radicals than cells can control. Under such circumstances, DNA damage is more likely to become a mutation, which can seriously damage the health of cells. In everyday life, we can wear a hat to minimize exposure to the sun or put on sunscreen lotions to absorb some of the UV radiation in sunlight.