Unit 2 - Genomes

Question 1

describe chromosome shape in bacterial and eukaryotic cells (2)

Answer 1

• bacterial chromosome is circular

- eukaryotic chromosome is linear

Question 2

describe a characteristic of bacterial and eukaryotic cells (2)

Answer 2

• bacterial cells are haploid cells

- eukaryotic cells are diploid cells

Question 3

haploid

Answer 3

• contain a single set of chromosomes (1 copy of DNA)

Question 4

diploid

Answer 4

• contains a double set of chromosomes (2 copies of DNA)

Question 5

describe DNA in bacterial and eukaryotic cells (2)

Answer 5

• DNA in both cells is double-stranded
• difference in packing between prokaryotes and eukaryotes is due to the difference in DNA structure and the vast differences in the amount of DNA (eukaryotes have far more in general)

Question 6

nucleoid-associated proteins

Answer 6

• packing proteins in bacteria

- proteins do not wrap the DNA around themselves

Question 7

histones

Answer 7

• packaging proteins in eukaryotes

- wrap DNA into a structure called nucleosomes, DNA is wrapped around histones

Question 8

How do bacteria package their DNA

Answer 8

• combination of supercoiling and proteins to package their circular genome into a nucleoid

Question 9

How is supercoiling achieved in bacteria? (3)

Answer 9

• (usually) by cutting one stand of the circular DNA, unwinding by a number of turns, and then resealing the DNA
• causes tension in DNA that is relieved by supercoiling, causing the entire genome to wind up into a smaller volume
• important because bacterial cells are generally small in size

Question 10

supercoiling (3)

Answer 10

• refers to the winding/unwinding of DNA by topoisomerases (an enzyme) in cells to add strain to DNA
• sometimes all DNA packaging is referred to as “supercoiling” of DNA
• more important in bacteria

Question 11

nucleoid

Answer 11

• in prokaryotes, a cell structure with multiple loops formed from supercoils of DNA

Question 12

negative supercoils (2)

Answer 12

• supercoils that result from underwinding

- in most organisms, DNA is negatively supercoiled

Question 13

positive supercoils

Answer 13

• supercoiling resulting from overwinding

Question 14

How is DNA packed in eukaryotic cells (2)

Answer 14

• cells also have topoisomerase II enzymes and the DNA is usually supercoiled
• DNA is linear and each DNA molecule forms a single chromosome

Question 15

describe the first level of packaging of DNA in eukaryotes (3)

Answer 15

• referred to as “beads on a string” where the nucleosomes are the beads and the DNA is the string
• also called a 10-nm fiber in reference to its diameter which is about 5x the diameter of the DNA double helix
• these are the areas of the genome that are transcriptionally active

Question 16

describe the second level of packaging in DNA in eukaryotes (2)

Answer 16

• chromatin is more tightly coiled forming a 30-nm fiber
• as chromosomes in the nucleus condense in preparation for cell division, each chromosome becomes progressively shorter and thicker as it coils onto itself to form a 300-nm coil, a 700-nm coil and finally a 1400-nm condensed chromosome

Question 17

chromatin (3)

Answer 17

• formed when huge numbers of nucleosomes are formed and collect together along a DNA strand
• DNA-protein complex formed by packaging of DNA with proteins
• found in eukaryotes

Question 18

chromatids/chromasomes

Answer 18

• coiled up chromatin in a dense form

Question 19

chromosome condensation

Answer 19

• progressive coiling of the chromatin fiber, an active, energy-consuming process requiring the participation of several types of proteins

Question 20

chromosome scaffold

Answer 20

• supporting protein structure in a metaphase chromosome

Question 21

describe the levels of chromosome condensation

Answer 21

1. DNA duplex (2 nm)
2. nucleosome fiber (10nm)
3. chromatin fiber (30nm)
4. coiled chromatin fiber (300nm)
5. coiled coil (700nm)
6. condensed chomatid (1400nm)

Question 22

compare the sizes of the eukaryotic chromosome and the bacterial nucleoid (2)

Answer 22

• the eukaryotic chromosome is vastly greater than the size of the bacterial nucleoid
• the volume of fully condensed human chromosome is 5 times larger than the volume of the bacterial cell

Question 23

genome (2)

Answer 23

• refers to all physical DNA within a cell (some exceptions exist), including DNA that does not code for anything
• genetic material transmitted from parent to offspring

Question 24

state basic definitions to differentiate between the terms genome, genotype, gene and phenotype

Answer 24

• the genome is all the genetic material of a cell/organism
• a genotype is all the genetic makeup of a cell/organism – the sequence of DNA
• a gene is the unit of hereditary information consisting of a DNA sequence
• a phenotype is an observable characteristic/trait

Question 25

genotype (4)

Answer 25

- genetic makeup of a cell or organism - set of instructions or DNA sequences - relates to the DNA sequences that code for protein or have some other type of function, but it can relate to any sequence of DNA that is important to us - the particular combination of alleles present in a an individual

Question 26

phenotype (4)

Answer 26

- expression of a physical, behavioural, or biochemical trait - an observable phenotype include height, weight, eye colour, etc - based on the genotype and the environment - what happens when the instructions are interpreted inside any given cell

Question 27

homozygous

Answer 27

- describes an individual who inherits an allele of the same type from each parent, or a genotype in which both alleles for a given gene are of the same type

Question 28

heterozygous

Answer 28

- describes an individual who inherits different types of alleles from the parent, or genotypes where the 2 alleles for a given gene are different

Question 29

in essence, what is the relationship between the genotype and the phenotype?

Answer 29

- genotype is the DNA's information and the phenotype is the result of the information being used

Question 30

alleles

Answer 30

- different forms of a gene, corresponding to different DNA sequences in each different form

Question 31

How can the regulation of the expression (gene regulation) of protein-coding genes affect the gene products?

Answer 31

- different gene products are made in different amounts in different cells at different times

Question 32

What is the result of differential gene expression? (2)

Answer 32

- allows some protein-coding genes to be deployed in different combinations to yield a variety of distinct cell types - proteins can interact with one another so that, even though there are relatively few types of protein, they are capable of combining in many different ways to perform different function

Question 33

How can a single gene yield multiple proteins?(2)

Answer 33

- alternative splicing (different exons are spliced together to make different proteins_ - post-translational modification (proteins undergo biochemical changes after they have been translated)

Question 34

gene (2)

Answer 34

- unit of heredity information consisting of a DNA sequence | - DNA sequence within a genome that can code for a protein or RNA

Question 35

what can contribute to major evolutionary changes?

Answer 35

- acquisition of whole new genes and the modification of existing genes and their regulation in subtle ways

Question 36

gene regulation

Answer 36

- the various ways in which cells control gene expression

Question 37

are all genes expressed in all cells and what does it mean? (4)

Answer 37

- no - this means that the phenotype may not be what you expect based on the presence of a gene in the genotype - cells in our body all share the same DNA but have vastly difference phenotypes as different sets of genes in the genotype are expressed in different cells

Question 38

Is there a correlation between the size of a genome and the complexity?

Answer 38

- NO, at least among eukaryotes

Question 39

Is the number of genes a good predictor of organism complexity?

Answer 39

-NO!

Question 40

If Species X has 100 million base pairs and Species Y has 96 million base pairs then:

Answer 40

- the genome of species X is larger than the genome of species Y

Question 41

how are genomes measured?

Answer 41

- measured in number of base pairs | - units are a kilobase (kb), a megabase (one million base pairs Mb), and a gigabase (a billion base pairs Gb)

Question 42

C-value paradox

Answer 42

- disconnect between genome size and organismal complexity

Question 43

C-value

Answer 43

- the amount of DNA in a reproductive cell

Question 44

polyploidy (3)

Answer 44

- condition of having more than 2 complete sets of chromosome in the genome - especially prominent in many groups of plants - occurs because of duplication or hybridization

Question 45

What is the principal reason for large genomes among some eukaryotes?

Answer 45

- genomes contain large amounts of DNA that do not code for for proteins, such as introns and DNA sequences that are present in many copies