Lecture 2

Question 1

How much are unrelated individuals similar ?

Answer 1

99.5%

Question 2

What is a gene ?

Answer 2

It’s a sequence of DNA that codes for a molecule / protein that has a function.

Question 3

Describe the structure of a nucleotide. On what side do we add nucleotides ?

Answer 3

It’s a pentose sugar with :
- base (A, T, C, G) at the 1’ carbon of sugar group
- hydroxyl group at the 3’ carbon
- phosphate group at the 5’ carbon
We can only add nucleotides at the 3’ side.

Question 4

Give the 2 groups of bases. How is base pairing determined ?

Answer 4

Purines : Adenine, guanine
Pyrimidine : Cytosine, thymine.
The hydrogen bonds determine the pairing !! (3 for CG, 2 for AT)

Question 5

How is the DNA pachaged ? What are its primary components? What are its functions?

Answer 5

Chromatin:
- made of histones and DNA
- package DNA, prevent DNA damage, control gene expression and DNA replication

Question 6

What is an entire single chromatin strand ? Two types.

Answer 6

Chromosom:
autosomes (22 pairs) and allosome (1 pair)

Question 7

Main differences between RNA and DNA

Answer 7

single stranded
uracil instead of thymine
ribose instead of pentose

Question 8

General steps of transcription

Answer 8

1) RNA polymerase binds to promoter DNA
2) RNA polymerase separates the two strands and adds complementary (to 3’-5’ DNA strand) nucleotides to form mRNA strand.
3)mRNA is freed when H bonds with DNA break

Question 9

Can one mRNA code for more than 1 protein ? What are exons and introns ?

Answer 9

Yes!
Exons = coding regions
Introns = non coding regions

Question 10

WHat happens in the post transcroptional processing ?

Answer 10

RNA splicing (introns removed).
5’ end capping, 3’ end polyadenylation (protects from degradation).
Mature mRNA leaves nucleus.

Question 11

3 steps of translation

Answer 11

1) initiation : ribosome binds at 5’ and moves in 3’ until start codon AUG
2) elongation : tRNA molecules arrive with amino acids (only accepted if right codon)
3) termination : when codon stop reached

Question 12

what happens to proteins after the translation ?

Answer 12

They fold

Question 12

How do we call expressed genes ?

Answer 12

active genes

Question 13

What is epigenetics ?

Answer 13

study of biological mechanisms that switch genes on and off (no alterations to the DNA sequence)

Question 14

What is G0 ?

Answer 14

resting phase (outside of cell cycle)

Question 15

What happens in the 4 cell cycle phases ?

Answer 15

G1: organelles duplicate and cell grows
S : DNA is replicated
G2 : assembly of necessary cytoplasmic materials, chromosomes are double checked
M : mitosis
Cytokinesis

Question 16

How many chromosomes do we have after DNA replication ?

Answer 16

Still the same, but twice the amount of chromatids (twice the amount of DNA)

Question 17

Steps of DNA replication

Answer 17

1) Helicase opens the DNA helix
2) DNA primase creates RNA primars where the DNA polymerase starts
3) DNA polymerase reads a strand and creates its counterpart (self checked). But polymerization only in 5’ to 3’ !!!
- leading strand
- lagging strand with okazaki fragments
4) Ligase binds fragments together

Question 18

Mitosis : steps and how long it takes

Answer 18

~1 hour.
1) prophase : chromosome condense, nucleus membrane breaks down, centrosome duplicated
2) Prometaphase : migration to equatorial plane. Spindle fibers bind to centromere of each chromosome
3) Metaphase : they align along the metaphase plate
4) Anaphase : sister chromatids are pulled to opposite ends
5) telophase : opposite of prophase
6) Cytokinesis

Question 19

Explain meiosis

Answer 19

Only for gametes (haploid sex cells).
1) DNA replication
2) Mitosis1 : homologous chromosomes are separated
3) Mitosis2 : Sister chromatides are separated