Lecture 4b

Question 1

Overall process of DNA–RNA…

Answer 1

Nucleus has 46 chromosomes
Each chromosome has hundreds of genes
Each gene has instructions on how to make a different RNA molecule, but the instructions are coded as DNA & you can’t take DNA out of the nucleus
Decode the instructions, write them as RNA (mRNA, rRNA, tRNA). RNAs leaves the nucleus
Bring all the RNAs to a ribosome which will use them to make the protein.

Question 2

Gene expression

Answer 2

Process by which information stored in ageneis used to make a geneproduct: mRNA, tRNA, rRNA, protein

Question 3

2 steps in gene expression

Answer 3

Transcription

Translation

Question 4

Transcribing DNA

Answer 4

Enzymes add RNA nucleotides to make an RNA molecule that is complementary to the DNA template strand (information from ageneis used to make RNA: mRNA, rRNA, tRNA)

Template DNA strand: strand of the DNA molecule whose info is used to make the RNA

Question 5

Transcription

Answer 5

information in DNA (genes) is used to make RNA molecules (mRNA, rRNA & tRNA).
DNA does NOT get turned into RNA
enzymes “read” the nucleotide sequence in DNA to make a complementary RNA stand.
Transcription make RNA (mRNA, rRNA, tRNA)

Question 6

Translation

Answer 6

Information in mRNA used to make a protein. mRNA does NOT get turned into a protein.
Info in mRNA used to make a polypeptide
-Sequence of amino acids in the polypeptide chain is determined by the
mRNA sequence
mRNA & tRNA meet rRNA at the ribosomes
Amino acids bonded together to make a protein

Question 7

Ingredients for translation

Answer 7

mRNA
tRNA
rRNA
Amino acids
Release factor
Ribosome
Energy

Question 8

mRNA

Answer 8

polynucleotide that determines the aa sequence of a polypeptide

Question 9

Codons

Answer 9

sequence of 3 mRNA nucleotides that corresponds to a specific amino acid or a stop signal

Question 10

tRNA

Answer 10

polynucleotide containing an anti-codon region that binds to codons AND another region that binds to amino acids

Question 11

Ribosomes

Answer 11

structures that contain binding sites for mRNA & tRNA and

contain rRNA that forms peptide bonds b/w amino acids

Question 12

Genetic code, codons

Answer 12

Set of codons, each of which corresponds to a specific amino acid or a stop signal
64 codons

3 stop codons: end translation, no aa added

61 codons for aa, 20 are distinct aa
includes 1 start codon: AUG which codes for the aa methionine: the 1st aa (at least initially) in all polypeptides

Question 13

mRNA determines ….

Answer 13

mRNA codon determines amino acid sequence
Order of codons → sequence of amino acids in the protein
1 codon codes for 1 aa

Question 14

Codon

Answer 14

group of 3 mRNA nucleotides

Question 15

tRNA sites

Answer 15

Anticodon region + aa binding site

Anticodon: pairs with complementary codon in mRNA

Question 16

where do the Amino acids, mRNA, tRNA meet up at ^

Answer 16

Amino acids, mRNA, tRNA meet up at the RIBOSOMES (contains rRNA)
Complex made up of 2 different subunits (each has rRNA + proteins)
Binding sites for mRNA & tRNA
rRNA joins the aa (amino acid) together (peptide bonds).
tRNA brings the aa to the ribosome: binds in complementary fashion to the mRNA

Question 17

Translation steps

Answer 17

1. mRNA binds to ribosome
2. Anti-codon region of 1st tRNA binds to codon of mRNA (“P site” of ribosome)
3. 2nd tRNA binds at the “A site” to the 2nd codon of mRNA
4. rRNA of ribosome forms peptide bond b/w aa 1 + 2
5. 1st tRNA (had Met) leaves without its amino acid

Question 18

Terminating translation

Answer 18

Occurs when the ribosome reaches a stop codon in the mRNA
Release factor (protein, not a tRNA) binds to the stop codon (same protein recognizes all 3 stop codons)
Binding promotes the breaking of the bond b/w tRNA & the completed polypeptide

Question 19

function of polypeptides

Answer 19

Polypeptides: peptide bonds join AA

Question 20

Where do the aa come from ?

Answer 20

Your cells can make some aa: these are called nonessential aa (since you don’t have to get them from your diet)
9 Essential aa: those that you can’t make at all or make enough of to meet your needs.
Have to get from diet
*** Essential aa & Nonessential aa are
EQUALLY IMPORTANT FOR THE CELLS