pro euk l

Question 1

euk vs pro: cell size

Answer 1

euk: larger, 10 to 100 micrometers
prok: smaller, 0.5 to 5 micrometers

Question 2

euk vs pro: nucleus

Answer 2

euk: nucleus with nuclear envelope presemt
pro: no true nucleus

Question 3

euk vs pro: genetic material

Answer 3

euk:
Linear DNA associated with many proteins;
Found in membrane bound nucleus;
No plasmids
pro:
Circular DNA associated with few histone-like proteins;
Found in a region of the cytoplasm known as the nucleoid region;
Plasmids present

Question 4

euk vs pro: type of ribosomes

Answer 4

euk: 80S, may be attached to ER or free in cytoplasm
pro: 70S, only found in cytoplasm

Question 5

euk vs pro: organelles present

Answer 5

euk: many membrane bound organelles present
pro: no membrane bound organelles

Question 6

euk vs pro: cell walls

Answer 6

euk: composed of cellulose in plants
pro: composed of peptidoglycan

Question 7

euk vs pro genome: size

Answer 7

euk: larger with more base pairs (10^7 to 10^11)
pro: smaller with less base pairs
(10^4 to 10^7)

Question 8

euk vs pro genome: appearance

Answer 8

euk: multiple, linear molecules
pro: single, circular molecule

Question 9

euk vs pro genome: molecule

Answer 9

both are double helix DNA

Question 10

euk vs pro genome: association with proteins

Answer 10

euk: large amounts of genome is associated with histones, scaffold proteins
pro: less amounts of genome is associated with histone-like proteins

Question 11

describe level of DNA packing/coiling in eukaryotic genome

Answer 11

high level:
negatively charged DNA double helix is associated with positively charged histones via electrostatic attraction: DNA is wound
around 8 histone proteins twice to form nucleosomes with linker DNA joining adjacent nucleosomes, forming a 10nm fiber/chromatin, which
coils around itself to form 30nm fibre/solenoid
the solenoid forms looped domains when associated with scaffold proteins, forming 300nm fibre, which then supercoils to form metaphase chromosome (at metaphase)

Question 12

describe level of DNA packing/coiling in prokaryotic genome

Answer 12

Relatively low:
DNA double helix is folded into looped domains by protein-
DNA associations
the looped domains further undergo supercoiling with the help of DNA gyrase and topoisomerase

Question 13

why do we need to package and coil DNA

Answer 13

1. to compact DNA to fit into the nucleus in eukaryotes or nucleoid in prokaryotes
2. to prevent DNA breakage or damage since DNA molecules move around alot during nuclear division
3. for regulation of gene expression in eukaryotes

Question 14

euk vs pro genome: location

Answer 14

euk: nucleus
pro: non membrane bound nucleoid region

Question 15

euk vs pro genome: presence of extrachromosomal DNA

Answer 15

euk: yes if mitochondrial and chloroplast circular DNA are considered
pro: yes of which are plasmids

Question 16

euk vs pro genome: number of genes

Answer 16

euk: 25000
pro: 4500

Question 17

pro vs euk genome: presence of introns

Answer 17

euk: many
pro: rare

Question 18

pro vs euk genome: presence of promoters

Answer 18

both have promoters present

Question 19

pro vs euk genome: presence of repeated sequences

Answer 19

euk: many such as telomeres/centromeres
pro: rare

Question 20

pro vs euk genome: presence of enhancers/silencers

Answer 20

euk: common
pro: rare

Question 21

pro vs euk genome: presence of operons

Answer 21

euk: few
pro: many

Question 22

describe structure of introns

Answer 22

• non coding DNA sequences found within a gene, specifically
  between exons in a specific
  segment of DNA (also present in
  pre- mRNA)
• only in eukaryotes

Question 23

describe function of introns

Answer 23

• enables a process
  called ‘alternative RNA splicing’
  to occur where different combinations of different exons
  of a single pre-mRNA can be
  joined such that different
  mature mRNAs are produced

so that one gene can now code for more than one polypeptide

Question 24

describe structure of promoter

Answer 24

• located just
  upstream of the
  transcription start
  site of a gene, hence it is called a proximal control element
• has critical elements
  e.g.1. TATA box, loacted
  upstream of transcription start
  site)
  e.g. 2. CAAT and GC boxes, located upstream of TATA but are not always present and are not critical in determining transcription frequency

Question 25

describe function of promoter

Answer 25

- recognition & binding site for general transcription factors which then recruits RNA Polymerase to form transcription initiation complex which initiates transcription -TATA box in promoter is where general transcription factoers bind to so it determines precise location of transcription start sitet site - CAAT and GC box improves the efficiency of promter

Question 26

describe structure of enhancers/silencer

Answer 26

are non coding regulatory DNA sequences usually located far away from the promoter (usually much further upstream or downstream), hence being called a distal control element

Question 27

describe function of enhancer

Answer 27

- recognition & binding site for activators - increase the frequency of transcription by promoting the assembly of the transcription initiation complex (with the help of DNA bending proteins that bend spacer DNA)

Question 28

describe function of silencer

Answer 28

- recognition & binding site for repressors - decrease the frequency of transcription by preventing the assembly of the transcription initiation complex

Question 29

what are specific transcription factors?

Answer 29

proteins with a DNA binding site that is complementary in shape and charge to a specific regulatory sequence of DNA which it binds to

Question 30

structure of telomeres

Answer 30

1- found at both ends/terminals of linear, eukaryotic chromosomes 2- non-coding DNA made up of a series of tandem repeat sequences which are a specific sequence of nucleotides occurring many times in a row 3- in humans, each repeat has the sequence 5’ TTAGGG 3’ 4- have a single stranded region at their 3’ ends known as the 3’ overhang and which due to a limitation of DNA polymerase, this region of DNA does not have acomplementary strand)

Question 31

describe role of telomeres in the end replication problem

Answer 31

Telomeres ensure that genes are not eroded and vital genetic information is not lost with each round of DNA replication due to the end replication problem. As DNA polymerase requires a free 3’OH of a pre-existing strand to add nucleotides, the last RNA primer on the lagging strand with DNA cannot be replaced with DNA. Hence, the DNA molecule shortens with each round of replication. Telomeres, which are non-coding sequences at the ends of linear chromosomes will be lost before any vital genetic information is. Since telomeres are non-coding, they can be lost without any deleterious effect.

Question 32

describe the role of telomeres in stabilising ends of chromosomes

Answer 32

2-Telomeres protect and stabilize the terminal ends of chromosomes by forming a loop using the 3’overhang. This prevents single-stranded terminal end of one chromosome from annealing to a complementary single-stranded terminal end of another chromosome, prevent fusing of 2 chromosomes. The formation of the loop also prevents the cell’s DNA repair machinery from detecting the chromosome as damaged DNA (i.e. double stranded breaks) and trigger apoptosis.

Question 33

describe telomere's role in their own extension

Answer 33

3-Telomeres allow their own extension, as they have a 3’ overhang which provides an attachment point for the correct positioning of the enzyme telomerase. Although telomeres shorten with every round of DNA replication, telomerase activity in germ cells, embryonic stem cells and cancer cells can maintain telomere length.

Question 34

how does telomerase work

Answer 34

A short 3-nucleotide segment of RNA within telomerase binds to part of a DNA repeat in the 3’overhang by complementray base pairing. 2. The adjacent part of the RNA within telomerase is used as a template to synthesise a short complementary 6-nucleotide DNA repeat. 3. Telomerase catalyses the formation of the phosphodiester bonds between the existing 3’OH group of existing DNA overhang and 5’ phosphate group of incoming deoxyribonucleotide After the repeat is made, telomerase translocates 6 nucleotides to the right in the 5’ to 3’ direction of the DNA overhang and begins to make another repeat. The above process is repeated such that a series of tandem repeats are made, elongating the telomere. 5.Then primase makes an RNA primer near the end of the telomere. DNA polymerase adds nucleotides to the 3’OH end of the primer and hence synthesizes a complementary strand . The nick is then sealed by ligase. The RNA primer is eventually removed.

Question 35

structure of centromeres

Answer 35

1. Constricted region on chromosome where kinetochore microtubules attach during nuclear division 2- non-coding DNA made up of a series of tandem repeat sequences

Question 36

function of centromeres

Answer 36

1- allow sister chromatids to adhere to each other 2- allow kinetochore proteins to attach and which in turn allow spindle fibres to attach so that sister chromatids/homologous chromosomes can align along the metaphase plate and subsequently be separated to opposite poles. Ultimately, allow s proper alignment and segregation of chromosomes.