Transcription/Translation

Question 1

What is the central dogma of molecular biology describing?

Answer 1

It describes the path that genetic information takes in the cell

Question 2

What is a gene?

Answer 2

The sequence of DNA nucleotides required to tell the cell how to make one type of protein

Question 3

What is a genome?

Answer 3

The collection of all the genes found in the DNA of a specie

Question 4

What’s the intermediate step between DNA and proteins?

Answer 4

RNA

Question 5

What is the process in which DNA converts to RNA?
Where does it take place?
Which enzyme is used?

Answer 5

Transcription
Nucleus
RNA polymerase (uses the law of complementary base pairs)

Question 6

What is the process in which RNA converts into proteins?
Where does it take place?
Which enzyme is used?

Answer 6

Translation
Cytosol and rough endoplasmic reticulum
Ribosome (uses the genetic codes -> combinaison of 3 RNA nucleotides called codons)

Question 7

What are proteins made of?

Answer 7

They are made of 20 different amino acids

Question 8

What are the differences between DNA and RNA?

Answer 8

In DNA: In RNA:
sugar groups: deoxyribose, ribose
double stranded, single stranded
A, T, C, G , A, U, C, G

Question 9

What is transcription?

Answer 9

The synthesis of RNA using the sequence of nucleotides contained in the DNA and the law of complementary base pairing

Question 10

Why does DNA need to be converted first into RNA? (2)

Answer 10

RNA is single-stranded, allowing it to exit the nucleus through the nuclear pores. (-> reach the ribosome, -> make proteins)
The enzymes that use RNA to make proteins (the ribosome) can only read RNA, not DNA

Question 11

For what process is transcription essential? And what is the definition of this process?

Answer 11

Gene expression. (The process of converting genetic information from DNA to functionnal products (proteins))

Question 12

Is only one RNA molecule made from a single gene?

Answer 12

No, many RNA molecules will be made from a single gene in DNA

Question 13

When does transcription begins and ends?

Answer 13

It starts at a promoter and ends at the terminator.

Question 14

What is a promoter?

Answer 14

A sequence of DNA nucleotides found before the coding sequence of a gene that allows the RNA polymerase to know where to start the transcription.
It always contains the sequence TATAAA

Question 15

What are the three steps of transcription?

Answer 15

Initiation, elongation, termination

Question 16

What are the two steps of initiation? (transcription)

Answer 16

1. RNA polymerase will first recognize and binds to the promoter
2. The two DNA strands will unwind only where RNA polymerase had bound to the DNA

Question 17

What are the two steps of elongation? (transcription)

Answer 17

1. RNA polymerase synthesizes an RNA strand using the nucleotides sequence in the DNA. Adds RNA nucleotides that are complementary to those found in the DNA
2. The two strands making up the DNA double helix re-attach to each other shortly after RNA polymerase passes

RNA polymerase moves along the DNA template strand, adding complementary RNA nucleotides.

The RNA strands grows in the 5’ to the 3’ direction

The DNA double helix re-attach after the passage of RNA polymerase

Question 18

What initiates termination? (transcription)

Answer 18

RNA polymerase comes to a terminator in DNA

Question 19

What happens once the terminator is reached? (3) (transcription)

Answer 19

The new RNA strand is released
RNA polymerase detaches from the DNA
The two DNA strands re-attach together

Question 20

Transcription is _________? What does it means?

Answer 20

Selective
All your ~25000 genes are not being transcribed by every type of cell all the time

(the cell only copies the genes it needs, not the entire DNA)

Question 21

Why is gene expression regulated? + Give two reasons why.

Answer 21

Not every cell needs to make the protein encoded by a gene all the time

• Not every type of cell in a multicellular organism needs the protein from every gene
• Even if a cell needs a protein from a particular gene, it might not need it all the time

Question 22

How can the expression of a gene be regulated?

Answer 22

Through regulating if it can be transcribed into RNA (Transcription factors)

Turning genes on or off by controlling how much mRNA is made.

Question 23

What does transcription factors help, or block?

Answer 23

RNA polymerase to bind the promoter and transcribe the gene (an activator)

or block it from binding and transcribing the gene (an repressor)

Question 24

How does the cell select which genes to transcribe?

Answer 24

Through gene regulation

The transcription factors (proteins) bind to the promoter or other nucleotide sequences around the promoter

Question 25

How do you know if the transcription factors help or block the transcription to occur? (depending on what)

Answer 25

Depends on the factor you are looking at and on which gene it is acting.

Question 26

Regulating expression based on cellular location example. (flies)

Answer 26

In animals, transcription factors control which segments of the animal develop which parts of the body. Ex: Antp is a **transcription factor** that causes legs to develop If Antp is **expressed in the head**, it causes the genes responsible for leg development to be transcribed instead of genes for antennae

Question 27

Regulating expression of a gene based on timing example

Answer 27

lacZ is a gene that codes for a protein that allows bacteria to break down lactose into glucose and galactose bacteria can only directly use glucose for energy, not lactose 2 different situations: 1) When glucose is available, the lacZ gene is not needed. -> A **repressor transcription factor** binds to the lacZ operator (near the promoter), **turning off** this gene. 2) When lactose is available, but not glucose, the lacZ gene will be needed to break lactose down to give glucose and galactose for energy. -> Lactose **binds** to the repressor transcription factor, **releasing it** from the operator. -> RNA polymerase can now bind the promoter and transcribe the gene.

Question 28

What is the role of a stop codon?

Answer 28

It tells the ribosome where to stop

Question 29

What is the role of the start codon?

Answer 29

It tells the **ribosome** where to **start translation**

Question 30

What is the start codon?

Answer 30

The 1st AUG is a start codon

Question 31

What are the stop codons?

Answer 31

UAA, UAG, UGA

Question 32

What is the open reading frame?

Answer 32

From the start codon to the stop codon.

Question 33

What is translation?

Answer 33

It is the last step in converting the instructions contained in your genes into proteins

Question 34

What are the three types of RNA involved in translation?

Answer 34

1) Messenger RNA (mRNA) 2) Transfer RNA (tRNA) 3) Ribosomal RNA (rRNA)

Question 35

What is the purposes of the first type of RNA involved in translation?

Answer 35

**(carries the protein-builing information into the cytoplasm)** mRNA carries the instruction for the ribosome on how to make a single protein from the generic code found in DNA. mRNA carries these instructions out of the nucleus into cytoplasm, where translation takes place.

Question 36

What is the structure of tRNA?

Answer 36

It is a **single strand**, folded into a "**t**-like" **shape** They have a **three-base anticodon** (complementary base-pairs to mRNA) , making sure that only the correct amino acid is added at a given time

Question 37

What is the purpose of transfer RNA?

Answer 37

It **carries** the individual **amino acids** to the **ribosome** every tRNA is specific to one amino acid only

Question 38

What is the purpose of ribosomal RNA?

Answer 38

It **combines with proteins** to form **ribosomes** In the ribosome, rRNA will **catalyze** the attachement of one amino acid to another

Question 39

What is the structure of rRNA?

Answer 39

The ribosomes has **two subunits**, one large subunit and one small subunit Each subunit is **made of** both **rRNA** and **proteins** The **large subunit** contains the **catalytic** **site** and the **two tRNA binding site** ("P-site" and "A-site")

Question 40

What are the three steps of translation?

Answer 40

1) Initiation 2) Elongation 3) Termination

Question 41

What does the initiation complex of translation includes?

Answer 41

The **small ribosomal subunit** The **tRNA** carrying the first amino acid of the protein (**methionine**)

Question 42

What does the initiation of translation form to begin? AND What is happening in initiation? (translation)

Answer 42

An initiation complex The **initiation complex** binds to an **mRNA** molecule The **large** ribosomal subunit arrives an the **methionine** tRNA binds to the first **tRNA binding site** on the large subunit (**P site**)

Question 43

What are the five steps of elongation? (translation)

Answer 43

The **tRNA** carrying the **second amino acid** binds in the second tRNA binding site, the **A site** The catalytic site then **catalyzes the chemical equation** that links the first amino acid and the second amino acid The **tRNA in the P site is ejected** and the tRNA from the **A site is moved** into the P site. The A site is now empty, and a tRNA carrying the **next amino acid moves in** (5' to 3' reading of mRNA) **This cycle repeats** for each amino acid of the protein

Question 44

What are the three steps in the termination stage? (translation)

Answer 44

- Termination occurs when the **ribosome** hits a **STOP codon** - A **release factor** (protein) binds to the **ribosome** - Ribosomal subunits **separate**, **mRNA** and the new **protein** are **released**