Chapter 5 Concepts

Question 1

What is the organisms genome?

Answer 1

The total genetic information carried by a cell or an organism (or the DNA molecules that carry this information).

Question 2

What is Chargaff’s Rule?

Answer 2

[A]=[T], [C]=[G]

Question 3

What type of bonds are formed between A-T and C-G basepairs?

Answer 3

hydrogen bonds (2 for A-T and 3 for G-C basepairs)

Question 4

Does the double stranded DNA have polarity? What does that mean?

Answer 4

Yes. Strands run in opposite directions

Question 5

Is the chromosome one long double stranded DNA molecule?

Answer 5

Yes

Question 6

What is on the 3’ end of the DNA?

Answer 6

Hydroxyl

Question 7

What is on the 5’ end?

Answer 7

phosphate

Question 8

What is a nucleosome?

Answer 8

DNA wrapped around protein core of 8 histone molecules (bonded ionically)

Question 9

How many times does DNA wrap around the nucleosome?

Answer 9

1.7 turns left handed

Question 10

How many histones comprise the nucleosome core?

Answer 10

8 histone proteins: 2-H2A, 2-H2B, 2-H3, 2-H4

Question 11

What part of the histone sticks out of the nucleosome and can be modified by acetylation, phosphorylation, methylation?

Answer 11

N terminal tail

Question 12

How would you define a gene?

Answer 12

A discrete segment of the genome composed of introns and exons that codes for a polypeptide or an RNA molecule and contains a promoter region and a terminator region

Question 13

Where are genes located?

Answer 13

Genes are located on the chromosomes

Question 14

How is gene structure in a prokaryote?

Answer 14

genes are often organized as functional units called operons, do not have introns, have specific promoter sequences and terminator sequences, a single mRNA in bacteria can encode multiple discrete polypeptides

Question 15

How is gene structure in a eukaryote?

Answer 15

genes located throughout 23 chromosomes in humans, made of introns and exons, and dispersed throughout the genome, have promoter region and terminator region and normally only encode a single polypeptide (but alternative splicing can result in addition of unique exons in a gene leading to splice variants that have additional polypeptides that are added to the protein–these are often in the form of domains)

Question 16

Do bacteria have introns and exons?

Answer 16

No

Question 17

What are exons?

Answer 17

parts of DNA sequence of a gene that will make up the mature mRNA.

Question 18

What are introns?

Answer 18

Segments of DNA between exons that are not included in the mature mRNA

Question 19

Approximately how many genes are in the human genome?

Answer 19

24,000

Question 20

What are the structures that cap the end of linear chromosomes?

Answer 20

7-methylguanosine CAP (unusual triphosphate linkage and methylation of the 2’ position)

Question 21

What is the enzyme that adds the ends to linear chromosomes?

Answer 21

Telomerase

Question 22

What is telomerase composed of?

Answer 22

It is an enzyme that is composed of both RNA and protein (carries its own primer as an RNA to anneal and extend the telomere repetitive ends)

Question 23

What is chromatin?

Answer 23

The complex of several classes of protein with nuclear DNA (proteins that bind to the DNA to form eucaryotic chromosomes, including histones, and other DNA binding proteins such as transcription factors)

Question 24

What are three main components of eucaryotic chromosomes that are associated with heterochromatin?

Answer 24

Centromere, Telomeres, Origins of Replication

Question 25

What is heterochromatin?

Answer 25

most highly condensed interphase chromatin

Question 26

What is euchromatin?

Answer 26

other form of interphase chromatin; less condensed form

Question 27

What are chromatin loops?

Answer 27

Loops are open areas of chromatin (not in heterochromatin) that contain genes that are actively expressed

Question 28

If an area of chromatin has high levels of methylation of cytosines, will it express genes in that region or not?

Answer 28

Gene will most often be silenced

Question 29

Where are ribosomes formed?

Answer 29

in the nucleolus that is located in the nucleus (ribosomes are made of RNA and proteins; ribosomal RNA is transcribed by RNA polymerase I)

Question 30

If an active gene area is moved next to a region of heterochromatin by translocation, what will happen to the expression of those genes?

Answer 30

silence the gene (heterochromatin is very tightly condensed)

Question 31

Where is heterochromatin located in the nucleus generally?

Answer 31

near the periphery

Question 32

Are there certain types of histones that are associated with specific types of heterochromatin?

Answer 32

yep (ex: HP-1 associated with heterochromatin, and there are specific histones for the centromere and origins of replication)

Question 33

How do histones interact with DNA and what types of amino acids are they enriched in?

Answer 33

DNA wraps around histone core 1.7 times left handed. “Enriched” or strengthened by positively charged amino acids (lysine, arginine) because they pull the chromatin in even tighter

Question 34

What does histone H1 do?

Answer 34

Pair of long tails at N and C terminal (C terminal attaches to chromatin pulling it in closer)

Question 35

How do chromatin remodelling complexes work?

Answer 35

use energy of ATP hydrolysis to change the position of the DNA wrapped around nucleosomes, decondensing underlying DNA (increases transcription)

Question 36

During mitosis, what level of compaction of the chromatin is achieved?

Answer 36

A lot. 10,000-fold

Question 37

What is the 30nm fiber?

Answer 37

In the 30nm fiber nucleosomes are arranged in groups of 6; a group of 6 nucleosomes has 1200bp of DNA

Question 38

What would be a way that cells could pass on to daughter cells a certain level of compaction of some chromatin and openness of other chromatin areas?

Answer 38

Reads methylation indicators (markers) and places methyl groups on the same C-G pair on the new daughter strand; methylation causes compaction (could silence gene)