Ch.6 DNA:Hereditary molecules of life

Question 1

Who is Friedrich Miescher?
What is his discovery?
What did he call the substance he used?

Answer 1

• Biochemist
• isolated non-protein substance from cell nuclei that was white sugary ,slightly acidic and contained phosphorus.
• He called this substance nuclein.

Question 2

Who is Frederick Griffith?

Answer 2

• Bacteriologist in 1928

Question 3

What did Frederick Griffith discover?

Answer 3

• the process of transformation in pneumonia-causing bacteria.

Question 4

What was the experiment Griffith used? His conclusion ?

Answer 4

He used mice and 2 streptococcus pneumoniae — encapsulated (S) or noncapsulated(R).
He concluded that living bacteria can acquire genetic material from dead bacteria, transforming the genotype of the live bacteria.

Question 5

What did Oswald Avery, Maclyn MacCarthy and Colin Macleod discover?

Answer 5

Showed that DNA was the transforming factor taken up by living bacteria.

Question 6

What did Erwin Chargaff discover?

Answer 6

1) DNA composition is species-specific
2) DNA of any species , amount of adenine (A) = thymine (T)
Amount of guanine (G) = cytosine (C)

Question 7

What did Alfred Hershey and Martha Chase discover? What is their conclusion?

Answer 7

Experimented on viruses that infect bacteria (bacteriophages) to determine whether hereditary material is DNA or protein.
They concluded that phage genetic material is DNA.

Question 8

What did Maurice Wilkins and Rosalind Franklin experiment? What is the conclusion?

Answer 8

• Conducted X Ray diffraction studies.
• bombarded crystals of purified dna with x rays and photographed diffraction patterns.
• indicates that dna has a helical structure

Question 9

What did James Watson and Francis Crick discover?

Answer 9

They constructed a molecular model of DNA. They built wire model of two strands twisted around each other— this concludes a double helix

Question 10

What is a DNA model?

Answer 10

• a ladder with steps and twisted into a spiral
• steps are pairs of nitrogeneous pairs joined by hydrogen bonds
• 2 strands DNA are complementary to each other and run antiparallel
• one strand is 5’ to 3’ direction and the other strand is the opposite

Question 11

What is a Purine?

Answer 11

Nitrogenous bases with a double ring structure

I.e adenine and and guanine are purines

Question 12

What is a pyrimidine?

Answer 12

Nitrogenous base with a single ring structure.

Ex. Thymine and cytosine

Question 13

Semiconservative replication

Answer 13

Mechanism of dna replication in which each of the two strands of parent dna is incorporated into a new double stranded dna molecule.

Question 14

Where does dna replication occur?

Answer 14

Interphase stage ( fast process that requires different enzymes)

Question 15

Replication Origin

Answer 15

A specific sequence of dna that acts as a starting point for replication

Question 16

Dna helicase

Answer 16

Unwinds the helix

Breaks hydrogen bonds b/w base pairs and prevents resealing

Question 17

DNA gyrase/topoisomerase

Answer 17

Class of enzymes that Relieves the tension brought by unwinding the dna during replication.

Question 18

Replication bubble

Answer 18

The separating of dna in both directions during replication

Question 19

Single stranded binding proteins (SSB)

Answer 19

Prevents parent dna strands from annealing to each other once they have been separated by helicase

Question 20

Replication fork

Answer 20

• the point of separation of the two parents dna strands during replication
• forms a y shaped structure

Question 21

RNA Primer

Answer 21

• Replication molecule that acts as a starting point for replication
• the beginning to the new strand
• made of a sequence of RNA about 10 nucleotides long

Question 22

RNA Primase

Answer 22

• Replication enzyme that produces rna primers

Catalyst for primer formation

Question 23

DNA Polymerase III

Answer 23

Enzyme that builds new dna strands from nucleotides.

Question 24

Leading strand

Answer 24

DNA strand that is copied in the direction toward the replication fork.
- on one strand (5’-3’) strand where dna is synthesized along the strand

Question 25

Lagging Strand

Answer 25

On the other strand (3’-5’) dna is synthesized discontinuously in a series of fragments.
- dna strand that is copied in the direction away from the replication fork

Question 26

What is Okazaki fragment

Answer 26

The piece of new dna on the lagging strand

Question 27

DNA Polymerase I

Answer 27

Enzyme that fills in gaps in the lagging strand b/w Okazaki fragments; proofreads the final strands.
Adds nucleotides to the end of the primer until it hits the 5’ end of another primer.

Question 28

DNA ligase

Answer 28

-connects newly synthesized DNA segment to the growing strand. It fills in gaps when RNA primer is later removed and replaced with DNA

Question 29

DNA Polymerase II

Answer 29

Enzyme that repairs damage to dna , including damage that occurs between replication events.

Question 30

Last step of dna replication

Answer 30

Proofreading: dealing with errors

DNA polymerase I and II backtracks, removes incorrectly paired nucleotides and continues to move forward.

Question 31

What is eukaryotic chromosome?

Answer 31

Consist of dna bound to histones.

Question 32

What is a histone?

Answer 32

-positively charged proteins

Negatively charged dna strands are attracted to them

Question 33

Nucleosome

Answer 33

Consists of 8 histones with dna strands wrapped around them

Question 34

Solenoid

Answer 34

• A group of 6 nucleosomes

- Further packing reduces the volume of six nucleosomes to 39nm chromatin fibres

Question 35

What are Telomeres?

2 things

Answer 35

1) repeating sequences of DNA found on the ends of chromosomes.
2) protect chromosomes from losing coding DNA during replication.

Question 36

What is Hayflick limit?

Answer 36

Telomeres length puts a limit on the number of times that dna an replicate and cell can divide.

Question 37

Cell senescence

Answer 37

The period in a cell’s lifespan when it loses the ability to divide and grow. When a cell reaches its Hayflick limit; cell aging.

Question 38

Psuedogenes

Answer 38

DNA sequences that are homologous with known genes but never transcribed

Question 39

LINEs(long interspersed nuclear elements)

Answer 39

Repetitive DNA sequences (6500bp) interspersed in the genome

Question 40

SINEs(short interspersed nuclear elements)

Answer 40

Repetitive DNA sequences (500 BP) in the genome

Question 41

What is a microsatellites (VNTR’s)

Answer 41

Non coding repeating sequences of dna

Question 42

Define Transposons?

Answer 42

• “jumping genes”

- Small segment of dna that can move to different position in the genome.

Question 43

Promoter region

Answer 43

Sequence of dna that binds rna Polymerase upstream of a gene.

Question 44

What is the difference between eukaryotes and prokaryotes in term of the genome

Answer 44

Prokaryotes:
- small and circular 
-all regions are coding, except fit promoter and operators
Presence of operons
Eukaryotes: 
- large and arranged in chromosomes 
-consists of coding and noncoding 
-absence of operons

Question 45

What is the difference between prokaryotes and eukaryotes about transcription?

Answer 45

Prokaryotes:

• coupled with translation
• lack of intron means excision

Eukaryotes:

• occurs in the nucleus
• introns excised by spliceosomes and Exxon’s joined together

Question 46

What is the difference between prokaryotes and eukaryotes in terms of translation?

Answer 46

Prokaryotes:

• commences with formyl-methionine
• ribosome recognizes Shine-Dalgarni sequence in RNA as binding site
• Ribosomes are smaller than in eukaryotes

Eukaryotes:

• commences with methionine
• Ribosome recognizes 5’ cap in mRNA as binding site
• ribosomes are larger than prokaryotes