Lecture 4

Question 1

What is transcription?

Answer 1

When we take the information encoded in gene in DNA and encode that information in mRNA.

Question 2

How is the transcription in prokaryotic cells?

Answer 2

Starting with the DNA, from that you code the mRNA.
Then that mRNA can be involved with the ribosome, that that’s the Translation! So no processing happens after RNA polymerase does its job.

Question 3

Where does the transcription happens in eukaryotic cells (structure)? How many steps (from what to what)?

Answer 3

Inside the nucleus.
Two steps:
From DNA -> to pre-mRNA
pre-mRNA -> to mRNA

which can then leave the nucleus and be translated into protein.

Question 4

The primary actor in the transcription process starts with?

Answer 4

The RNA polymerase.

Question 5

What does the RNA polymerase do?

Answer 5

It creates a sequence that will become a nucleotide sequence, then it will become the mRNA.

Question 6

Where does RNA polymerase starts the process?

Answer 6

It attaches to a sequence of the DNA known as promoter.
Then it separates the strands.
After it can code for RNA.

Question 7

How can the RNA polymerase function when separating the strands? (Hint. DNA replication)

Answer 7

Only to 5’ to 3’ direction by adding more nucleotides.

Question 8

Template strand? Coding strand? Which one does RNA polymerase binds?

Answer 8

RNA polymerase binds to the template strand creating same pair as with the coding strand.

Question 9

Where does the RNA polymerase stops?

Answer 9

'’Terminator’’ creates signals to the RNA polymerase that it’s time to stop.

Question 10

So, the RNA polymerase has stopped its process and formed into ‘‘pre-mRNA’’. What happens next? (Only in eukaryotic cells)

Answer 10

At the start:
A 5’ cap, which is a modified guanine, which helps in the translation process.
At the end:
A 3’ end has a poly A-tail.

Question 11

How does the pre-mRNA splicing happens?

Answer 11

Introns are spliced out, because they do not code for the protein.

Question 12

So basically how does the pre-mRNA proccessing happens?

Answer 12

You add the 5’ cap, you add the 3’ end poly A-tail and exons between them.

Question 13

How do you go from a gene to a protein?

Answer 13

From gene to mRNA. (transcription)

From mRNA to Protein. (Translation)

Question 14

Where does the translation to a protein happen?

Answer 14

In a ribosome, where it will be translated into a polypeptide sequence.

Question 15

What is ribosome made of?

Answer 15

Made up of proteins + ribosomal RNA (rRNA)

Question 16

What does the ribosome do to the mRNA?

Answer 16

It travels along the mRNA, from the 5’ end to the 3’ end, reading it, and taking that information, turning it into a sequence of amino acids.

Question 17

How does the reading of mRNA in ribosome happens?

Answer 17

Each of the three nucleotides, a codon (example AUG), the information is encoded in the nitrogenous bases.

Question 18

How do we get from a codon to a specific amino acid? Amount of amino acids?

Answer 18

There are 22 standard amino acids, 21, found in eukaryotic cells. 64 permutations, so more than enough for coding for the amino acids.
61 codes for amino acids, 3 STOPS the process.

Question 19

How does the amino acids bind together to form a polypeptide? How do they get matched with a right codon?

Answer 19

With transfer RNA (tRNA).
Each of the tRNA’s combine to a specific amino acid.
And with their anti-codons, the pair with the right codon.

Question 20

How does the proper codon - tRNA combination chain actually forms?

Answer 20

With three steps:

From left to right:
E-site, P-site, A-site.

Question 21

What is the A-site?

Answer 21

A-site is where the appropriate tRNA initially bounds to an amino acid.

Question 22

What happens when the bound of a amino acid happens in the A-site?

Answer 22

You have a peptide bond form between the two amino acids, and the ribosome can move to the right. So the A-site goes to the P-site.

Question 23

What are P- and E-sites?

Answer 23

P-site is where the polypeptide chain is actually formed.

E-site is ready to exit from the ribosome.

Question 24

How does antibiotics work?

Answer 24

In prokaryotic cells in ribosomes we can find molecules that hurt the function of ribosomes.
The antibiotics can interrupt the translation process in the bacteria but not in the cells you want to keep.

Question 25

What is a protein function? (Derived from?)

Answer 25

Protein function is derived from three-dimensional structure.
Three-dimensional structure is specified by amino acid sequence.

Question 26

What are proteins structures?

Answer 26

Primary, secondary and tertiary structures.

Question 27

Something about primary protein structure?

Answer 27

The amino acids linked by peptide bonds into linear chain, based on mRNA sequence.

Question 28

Something about secondary protein structure?

Answer 28

Various arrangements resulting from the folding of localized parts of a polypeptide chain.
Structure is stabilized by hydrogen bonds.

Question 29

Something about tertiary protein structure?

Answer 29

The overall conformation of a polypeptide chain.

The three-dimensional arrangement of all its amino acid residues.

Question 30

Protein structure is stabilized by?

Answer 30

Hydrophobic interactions between the nonpolar side chains.
Hydrogen bonds between polar side chains.
Peptide bonds.

These stabilizing forces hold together elements of secondary structure.

Question 31

How does the folding of proteins happen?

Answer 31

It is mediated by proteins - chaparones.

Chaparones bind to the amino (M) terminus of the growing polypeptide chain, stabilizing it in an unfolded configuration until synthesis of the polypeptide is completed.

Question 32

What happens after the synthesis of the polypeptides is completed?

Answer 32

The complete protein is then released from the ribosome and is able to fold into its correct three-dimensional conformation.

Question 33

What are isomerases functions?

Answer 33

• Catalyse protein folding
• Catalyse the isomerization of peptide bonds between proline residues
• Stabilizes folded structures in many proteins

Question 34

What is proteolysis?

Answer 34

Cleavage of the polypeptide chain.

Proteolytic modification play role in the translocation of many proteins across membranes.

Question 35

What is glycosylation?

Answer 35

A process where proteins are modified by the addition of sugar.
Glycosylation is initiated in the endoplasmic reticulum before translation is complete.

Question 36

Some proteins are modified in the eukaryotic cells by?

Answer 36

Attachment of lipids to the polypeptide chain.

Question 37

Alpha1-antitrypsin deficiency leads to?

Answer 37

Lung and liver damage.
Changed forms of this protein fail to complete proper folding and are retained in the ER.
It accumulates in the ER of hepatocytes – the site of synthesis
– resulting in liver damage

Question 38

How does Huntington’s disease forms?

Answer 38

Caused by an unstable expansion of a CAG repeats within the coding region of the HTT gene and results in an elongated stretch of glutamine near the N- terminus of the protein.

Question 39

Genes in DNA are expressed when

Answer 39

They are read and transcribed into RNA, which is translated into protein by structures called ribosomes.

Question 40

What proteins do?

Answer 40

Determines cell’s characteristics and functions.