EST-ACT-AP
BIOLOGY
Molecular Genetics (DNA)
Replication and Protein Synthesis
Molecular Genetics (DNA)
DNA
RNA
Double helix (two complementary strands paired
Single-stranded helix.
by hydrogen bond).
Polymer made of repeating units (nucleotides)
Polymer made of repeating units (nucleotides)
5-carbon sugar (deoxyribose)
5-carbon sugar (ribose)
Nitrogenous bases: adenine (A), thymine
Nitrogenous bases: adenine (A), uracil (U),
(T), cytosine (C), and guanine (G).
cytosine (C), and guanine (G).
Only one type
There are 3 types: mRNA (messenger RNA),
TRNA
(transfer RNA), and rRNA (ribosomal RNA).
RNA Model
Transfer RNA (tRNA)
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
carries messages directly
carries amino acids to the
It's structural and makes up
from DNA in the nucleus to
mRNA at the ribosome to form
the ribosome along with
the
a
proteins
cytoplasm during the making
polypeptide
of protein
The triplet nucleotides of
The triplet nucleotides of tRNA
mRNA (such as AAC or UUU)
are complementary to the
are called codons.
codons of mRNA and are called
anticodons.
DNA Replication in Eukaryotes
❖ James Watson and Francis Crick discovered the double helix shape of DNA. ❖ Semi
conservative process that produce hybrids DNA (one old and one new strand). ❖
Replication occurs during interphase (S-phase) in the cell life cycle (In nucleus). ❖
Helicase enzyme is used for Separation of DNA double Helix.
❖ DNA polymerase enzyme is used for DNA replication.
❖ Ligase enzyme Link the two sections of DNA during replication.
❖ Telomerase enzyme can restore the original length of chromosome by adding Telomers.
∙ DNA separate at the hydrogen bonds that connect the two strands of the double helix. ∙ DNA polymerase
also fixes errors and minimizing the occurrence of mutations. ∙ Each strand of DNA serves as a template for
the new strand according to the base pairing rules: A with T and C with G.
So, if a strand of DNA to be copied is AAA TCG GAC ATT ACG
then the new strand is
∙ Purines (Adenine and guanine) and Pyrimidines (Thymine, Cytosine and Uracil). ∙ Three
hydrogen bonds form between (G and C) …. Make DNA more stable at high temperature
∙ Two hydrogen bonds form between (A and T) or (A and U).
DNA Replication in Eukaryotes
Protein Synthesis (Gene Expression)
There are three main steps:
I- Transcription
∙ Process by which DNA makes RNA by RNA polymerase
∙ occurs in the nucleus
∙ The triplet code in DNA is transcribed into a codon sequence in messenger RNA (mRNA) If
the sequence in DNA triplets is
AAA TAA CCG GAC AAG Then the complementary sequence of codons in
mRNA is:
This DNA base sequence directs is transcribed into a codon sequence in messenger RNA
(mRNA)
3’ …A-G-T-T-G-A… 5'
Transcription
II- RNA Processing (Splicing)
∙ Process by which the enzymes remove pieces of RNA that do not code for any protein. ∙
Occurs in the nucleus
∙ Non-coding regions (introns) are removed
∙ Coding regions (exons) are pieced back together to form the final transcript. ∙ The mRNA
that leaves the nucleus to the ribosomes through nucleus membrane pores.
III- Translation
∙ Process by which the mRNA sequence is converted into an amino acid
∙ Occurs in the ribosome in the cytoplasm.
∙ Amino acids present in the cytoplasm are carried by tRNA molecules to the codons of the mRNA strand at
the ribosome
∙ Some tRNA molecules can bind to two or more different codons. For example, codons UCU, UCC, UCA,
and UCG all code for a single amino acid, serine.
∙ Most codons code for specific amino acids
❖ There are four special codons:
a) One start codon AUG
(met)
b) Three stop codon UGA,
UAG, UAA
❖ 1 gene 1 protein
3 nucleotides 1 amino acid
(triplet codon)
Translation
Protein Synthesis
Example: Determine what amino acid sequence will form if the DNA sequence is:
TAC AAA CAA TCA
Transcription
RNA Processing
Translation
RNA polymerase
DNA RNA
By enzymes
mRNA shorter mRNA
By tRNA
mRNA amino acids
Occurs in the nucleus
Occurs in the nucleus
Occurs in the ribosome
Assignment 10
Questions 1-4 refer to the following mRNA codons and their respective amino acids. (A)
AUG (met).
(B) UAA (stop).
(C) UGG (tip) (D) GGG (ala) (E) UUU (phe)
1. The corresponding DNA nucleotide sequence is ATT.
2. This is the codon that causes no additional amino acid to be added to a growing polypeptide. 3.
This is the start codon for the beginning of a polypeptide chain.
4. The corresponding tRNA anticodon is AAA.
5. Transcription is best defined as a process that.
(A) Creates an exact replica of DNA.
(B) Produces tRNA from an mRNA template,
(C) Indicates the direction of DNA synthesis.
(D) Maintains the tertiary structure of DNA.
(E) Synthesizes mRNA from a DNA template.
6. What is a section of DNA that codes for a protein called
(A) gene
(B) allele
(C) Chromosome
(D) plasmid
(E) transcription
7. The best definition of a gene is that it is:
(A) A sequence of amino acids which makes up a polypeptide
(B) A sequence of ribonucleotides which makes up a DNA and codes for polypeptide
(C) A sequence of deoxyribonucleotides which makes up the DNA and is transcribed to RNA then translated to a
polypeptide
(D) Any sequence of deoxyribonucleotides which makes up the DNA
(E) Any sequence of ribonucleotides which makes up a DNA
Questions 8-9
Homophiles influenza DNA is made up of about 1,800 kilo base pairs organized into about 1,750 genes. The DNA is rich
in cytosine.
8. If the genes of H. influenza were all located on a single strand of the double helix and were adjoining one another end
to end, an average gene would include approximately how many bases?
(A) 10
(B) 100
(D) 10,000 (E) 1,000,000
(C) 1,000
9. The DNA of H. influenzae is enriched in two nitrogenous bases. One of these is (A)
Adenine.
(B) ATP.
(C) Guanine.
(D) Thymine.
(E) Uracil.
Questions 10-11:
The figure below represents an important process that occurs in the
human cell. Refer to the figure to answer the questions that follow.
10. What process does this figure represent?
(A) DNA replication
(B) RNA processing
(C) Protein synthesis
(D) Transcription
(E) None of the above
11. The numbers 123 on the tRNA must be replaced with the following anti-codon: (A)
UAC
(B) CAU
(C) AUG
(D) UAG
(E) AUC
Questions 12-15 refer to the diagram showing how a bacterium makes a protein from the instructions in DNA.
12. The ribosome is represented by which labeled structure?
(A) 1
(B) 3
(C) 5
(D) 6
(E) 7
13. Messenger RNA is represented by which labeled structure?
(A) 1
(B) 2
(C) 4
(D) 5
(E) 6
14. A hydrogen bond is represented by which labeled structure?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5
15. Which of the labeled structures contains both protein and RNA?
(A) 1
(B) 2
(C) 4
(D) 5
(E) 6
Questions 16-18:
(A) Transcription
(B) Translation
(C) DNA replication
(D) RNA processing
(E) Mutation
16. This process takes place in the cytoplasm.
17. This process takes place during the S phase of the cell cycle.
18. The mRNA is ready to exit the nucleus.
19. A tRNA molecule specialized for transfer of the amino acid serine has the anticodon AGA. It will specially bind to an
mRNA molecule with which of the following codons?
(A) AGA
(B) TCT
(C) TGT
(D) UCC
(E) UCU
Questions 20-23
(A) DNA
(B) rRNA
(C) mRNA
(D) tRNA
(E) RNA polymerase
20. The molecule that carries the genetic information from one cell generation to the next. 21. The
product of transcription that determines the sequence of amino acids in a polypeptide chain. 22. A
nucleic acid that bonds temporarily with a specific amino acid during protein synthesis. 23. The protein
that carries out transcription.
24. If guanine makes up 28% of the nucleotides in a sample of DNA from an organism, then thymine would make up ______
% of the nucleotides.
(A) 0
(B) 22
(C) 28
(D) 44
(E) 56
3’ …A-G-T-T-G-A… 5'
25. The DNA base sequence above directs the synthesis of which of the following base sequences in messenger RNA? (A)
5' ....-A-G-T-T-G-A … ...3'
(B) 5' .... -U-C-A-A-C-U … ...3
(C) 5’ .... -U-T-A-A-T-U … ...3'
(D) 5' .... -T-C-T-T-C-T ... ....3
(E) 5' .... -C-A-T-T-A-C … ...3'
Questions 26-29 refer to the following illustration of protein synthesis in a mammalian cell.
26. A strand of mRNA being translated.
27. A polypeptide being synthesized.
28. A barrier to diffusion of large proteins from nucleus to cytoplasm.
29. A structure that contains a lipid bi layer.
30. The ribosomes of a cell are of primary importance for
(A) DNA replication.
(B) Transcription.
(C) Translation.
(D) Translocation.
(E) Repression.
31. A function of transfer RNA is to
(A) Receive the genetic information from nuclear DNA.
(B) Store the genetic information in the nucleus.
(C) Store RNA in the ribosomes.
(D) Transfer the genetic information from the nucleus to the cytoplasm.
(E) Position amino acids for protein synthesis by pairing with codons in messenger RNA.
Questions 32-34:
Refer to this sketch of prokaryotic DNA as it commonly undergoes replication and transcription simultaneously.
32. If 2 is thymine, then B must be
(A) guanine.
(B) cytosine.
(C) thymine.
(D) adenine.
(E) uracil.
33. If 5 is adenine, then E must be
(A) guanine.
(B) cytosine.
(C) thymine.
(D) adenine.
(E) uracil.
34. How does the process shown differ in a eukaryotic cell?
(A) Eukaryotic ce lls do not carry out transcription.
(B) Eukaryotic cells do not carry out replication.
(C) Eukaryotic cells do not carry out both transcription and replication.
(D) Eukaryotic cells carry out both processes, but they do not occur at the same time. (E)
Eukaryotic cells carry out both processes in the Golgi body.
35. The codon GUG in messenger RNA has been transcribed from which of the following sequences in DNA? (A)
GAG.
(B) CAC.
(C) TAT.
(D) CTC.
(E) ATA.
36. The production of different cell types in a multicellular organism is regulated by which of the following
mechanisms?
(A) Ribosomes preferentially translate some mRNAs and not others.
(B) Proteins present in the cytoplasm are degraded at different rates.
(C) Specific sets of mRNAs are produced in a particular cell type.
(D) Specific mRNAs are the cytoplasm most be modified to allow their translation. (E)
Only some RNAs are modified and transported to the cytoplasm.
Assignment 10 Answers
Molecular Genetics (DNA)
31
1
B
11
C
21
C
2
B
12
C
22
D
32 D
3
A
13
C
23
E
E
4
E
14
B
24
B
34
D
5
E
15
D
25
B
35
B
6
A
16
B
26
D
36
C
7
C
17
C
27
E
8
C
18
D
28
A
9
C
19
E
29
A
10
C
20
A
30
C
a
33
E
Assignment 10 Student Answers
Student Name: .
Molecular Genetics (DNA)
1
11
21
2
12
22
3
13
23
33
4
14
24
34
5
15
25
35
6
16
26
36
7
17
27
18
28
9
19
29
10
20
30
8
D
31
32