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Questions and Answers
What is the first step in the elongation phase of translation?
What is the first step in the elongation phase of translation?
What occurs during the translocation step of translation elongation?
What occurs during the translocation step of translation elongation?
What is the role of the release factor during termination of translation?
What is the role of the release factor during termination of translation?
During translation, what kind of modifications can a protein undergo post-translationally?
During translation, what kind of modifications can a protein undergo post-translationally?
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Which type of mutation does not alter the protein sequence?
Which type of mutation does not alter the protein sequence?
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What is the bond between the sugar and the phosphoryl group in a nucleotide called?
What is the bond between the sugar and the phosphoryl group in a nucleotide called?
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Which carbon on the sugar is phosphorylated in a nucleotide?
Which carbon on the sugar is phosphorylated in a nucleotide?
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Which statement accurately describes a purine base?
Which statement accurately describes a purine base?
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In DNA and RNA, the nitrogenous base is β-attached to which sugar?
In DNA and RNA, the nitrogenous base is β-attached to which sugar?
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What type of bond connects the 3' carbon of one nucleotide to the 5' carbon of another nucleotide in a DNA chain?
What type of bond connects the 3' carbon of one nucleotide to the 5' carbon of another nucleotide in a DNA chain?
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What type of structure do pyrimidine bases have?
What type of structure do pyrimidine bases have?
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What forms the backbone of a DNA or RNA polymer?
What forms the backbone of a DNA or RNA polymer?
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What is the role of small nuclear RNAs (snRNAs) in the spliceosome?
What is the role of small nuclear RNAs (snRNAs) in the spliceosome?
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What do snRNAs specifically bind to during the splicing process?
What do snRNAs specifically bind to during the splicing process?
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What does it mean when the genetic code is described as degenerate/redundant?
What does it mean when the genetic code is described as degenerate/redundant?
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Which characteristic of the genetic code ensures that each codon uniquely corresponds to one amino acid?
Which characteristic of the genetic code ensures that each codon uniquely corresponds to one amino acid?
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Which of the following accurately describes the structure of the spliceosome?
Which of the following accurately describes the structure of the spliceosome?
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What is the main function of the spliceosome in gene expression?
What is the main function of the spliceosome in gene expression?
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What does the term 'nonoverlapping' indicate about codons in the genetic code?
What does the term 'nonoverlapping' indicate about codons in the genetic code?
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In the context of the genetic code, what does 'commaless' refer to?
In the context of the genetic code, what does 'commaless' refer to?
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How do snRNAs interact with pre-mRNA?
How do snRNAs interact with pre-mRNA?
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What is the significance of the binding of snRNAs to introns?
What is the significance of the binding of snRNAs to introns?
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How many bases are contained in each codon of the genetic code?
How many bases are contained in each codon of the genetic code?
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Why is it important that the genetic code is specific?
Why is it important that the genetic code is specific?
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Which component is essential for the assembly of the spliceosome?
Which component is essential for the assembly of the spliceosome?
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What type of RNA is involved in forming complexes with proteins that mediate splicing?
What type of RNA is involved in forming complexes with proteins that mediate splicing?
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Which property of mRNA prevents the sharing of bases between consecutive codons?
Which property of mRNA prevents the sharing of bases between consecutive codons?
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Which statement about the spliceosome is true?
Which statement about the spliceosome is true?
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What would happen if the genetic code were not redundant?
What would happen if the genetic code were not redundant?
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Given that the genetic code is commaless, how are codons organized?
Given that the genetic code is commaless, how are codons organized?
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Which of the following best describes the interaction between snRNAs and splicing?
Which of the following best describes the interaction between snRNAs and splicing?
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What role does redundancy in the genetic code play in biological systems?
What role does redundancy in the genetic code play in biological systems?
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What is the primary function of messenger RNA (mRNA)?
What is the primary function of messenger RNA (mRNA)?
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Which stage of transcription involves RNA polymerase binding to the promoter?
Which stage of transcription involves RNA polymerase binding to the promoter?
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What modification is added to the 5' end of eukaryotic mRNA?
What modification is added to the 5' end of eukaryotic mRNA?
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What is a characteristic of transfer RNA (tRNA)?
What is a characteristic of transfer RNA (tRNA)?
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During RNA splicing, which of the following is removed from the primary mRNA?
During RNA splicing, which of the following is removed from the primary mRNA?
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Which type of RNA acts as a structural and functional component of the ribosome?
Which type of RNA acts as a structural and functional component of the ribosome?
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What is a property of the 3' poly(A) tail added to eukaryotic mRNA?
What is a property of the 3' poly(A) tail added to eukaryotic mRNA?
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What is the role of spliceosomes during RNA splicing?
What is the role of spliceosomes during RNA splicing?
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In the Central Dogma, the flow of genetic information goes from DNA to which of the following?
In the Central Dogma, the flow of genetic information goes from DNA to which of the following?
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Study Notes
Nucleic Acids - Structure & Function
- DNA and RNA are long polymers
- Each nucleotide is a monomer
- Each nucleotide consists of:
- A nitrogeneous heterocyclic base
- Purine
- Pyrimidine
- A 5-carbon sugar
- Ribose
- Deoxyribose
- A phosphoryl group
- A nitrogeneous heterocyclic base
- Both the base and sugar have ring structures
- Sugars are numbered with 'prime' (')
- Bases are numbered without 'prime'
- A covalent bond between sugar and phosphoryl is a phosphoester bond
- A bond between base and sugar is a β-N-glycosidic linkage joining the 1' carbon of sugar and N of the base
- Nitrogenous bases are heterocyclic amines
- Cyclic compounds with at least one nitrogen atom in the ring
- Purines are double rings: a 6-member ring fused to a 5-member ring
- Adenine (A)
- Guanine (G)
- Pyrimidines consist of a single 6-membered ring
- Cytosine (C)
- Uracil (U) - found in RNA
- Thymine (T) - found in DNA
- DNA and RNA are polymers of nucleotides.
- Nitrogen base is β-attached to:
- Ribose (RNA)
- Deoxyribose (DNA)
- The sugar is phosphorylated at carbon 5'.
Prokaryotic Chromosomes
- Prokaryotes are single-celled organisms without membrane-bound organelles
- Chromosomes are DNA pieces with genetic instructions (genes)
- Prokaryotic chromosomes are:
- Single, circular/loop DNA molecules
- Supercoiled
- Attached to the inner membrane of the prokaryote
- Located in a nucleoid region of the cytoplasm (not a membrane-bound nucleus)
Eukaryotic Chromosomes
- Eukaryotic chromosomes are linear and vary in number and size
- They have a true nucleus surrounded by a nuclear membrane
- DNA is wrapped around histone proteins to form nucleosomes
- DNA appears as "beads on a string"
- Nucleosomes coil into 30nm fibres
- Further coiling leads to 300nm fibres
RNA Structure
- RNA's backbone is composed of S-P-S-P
- RNA is primarily single-stranded;
- Ribose replaces deoxyribose
- Uracil replaces thymine
- Base pairing (A=U) and (C=G) forms double-stranded regions (viruses)
DNA Replication
- DNA must be replicated before cell division
- Each daughter cell needs a copy of each gene
- The replication process must produce an accurate copy of the original genetic information
- Mistakes in replication can cause lethal mutations
- Replication is catalyzed by DNA polymerase
- The molecule has an original/parent strand and newly synthesized strand
- Replication is semiconservative, resulting in two new DNA helices each with one original strand
- Bacterial DNA replication begins at a unique sequence (replication origin)
- Replication moves bidirectionally, at a rate of 500 nucleotides/second
- The position where nucleotides are added is the replication fork.
- There are two replication forks that move in opposite directions
Details of DNA Replication
- Helicase separates the strands by breaking hydrogen bonds
- Positive supercoiling is relieved by topoisomerase
- Single-strand binding proteins prevent strands from rejoining (reannealing)
- Primase synthesizes RNA primers needed for DNA polymerase
- DNA polymerase III elongates the new strands
- DNA polymerase I removes RNA primers and replaces them with DNA nucleotides
- DNA ligase joins together Okazaki fragments on the lagging strand
DNA Polymerase Reaction
- DNA polymerase III reads parental DNA/template and creates a complentary strand
- A pyrophosphate group is released during the polymerization
- A new phosphoester bond is formed between the 5' phosphoryl group and the 3'−OH group of the existing nucleotide. This is a 5' to 3' direction.
DNA Replication - Influencing Factors
- The two DNA strands are antiparallel.
- DNA polymerase III can only work in the 5' to 3' direction
- Small RNA primers are required for a starting point of DNA replication
DNA Replication - Leading Strand
- A single RNA primer is produced at the replication origin
- DNA Polymerase III continuously adds nucleotides in the 5' to 3' direction
DNA Replication - Lagging Strand
- Many RNA primers are produced as the replication fork moves along the molecule
- DNA polymerase III catalyzes elongation of the new strand in the 5' to 3' direction
- Okazaki fragments are formed, and then joined by DNA ligase
- The process repeats with another primer made at a new location of the replication fork
- RNA primers are removed, and the gaps are filled by DNA polymerase I
- The fragments are sealed by DNA ligase
Replication Fork - Detailed View
- The lagging strand is synthesized discontinuously and in the opposite direction to the replication fork movement.
- Various enzymes are involved in the process, including DNA polymerase III, DNA polymerase I, primase, ligase, helicase, single-strand binding proteins and topoisomerase.
- Okazaki fragments are formed during synthesis on the lagging strand, which are later joined together by the DNA ligase enzyme.
Central Dogma
- In cells, genetic information contained in DNA flows in one direction to RNA to protein
- Transcription is making a copy of a strand of DNA
- Translation is converting the information from one language of bases to another of amino acids
Classes of RNA Molecules
- Messenger RNA (mRNA): a complementary copy of a gene that directs the amino acid sequence of proteins
- Ribosomal RNA (rRNA): a structural and functional component of ribosomes, forming ribosomes by reacting with proteins. It has 3 types in prokaryotes & 4 types in eukaryotes
- Transfer RNA (tRNA): transfers amino acids to the site of protein synthesis
Transfer RNA (tRNA)
- There is at least one tRNA for each amino acid incorporated into a protein
- tRNA is single-stranded and typically about 80 nucleotides long
- The overall structure is a cloverleaf
- It has intrachain hydrogen bonding between A=U and C=G bases; contains rare bases like D, T, Y, and Ψ
- The 3' end of the molecule has a conserved CCA-3' sequence for amino acid binding
Aminoacyl tRNA Synthetase
- It catalyzes the attachment of a tRNA molecule to its respective amino acid.
- There is at least one aminoacyl tRNA synthetase for each amino acid.
Protein Synthesis
- Protein synthesis is called translation
- It is carried out on ribosomes which are constructed from rRNA and proteins.
- mRNA is translated 5' to 3'
- Protein synthesis occurs in multiple places on a single mRNA molecule, forming a polysome
- tRNA binds specific amino acids by aminoacyl tRNA synthetase enzyme
- tRNA recognizes its complementary codon on the mRNA
Genetic Code
- Degenerate/redundant: more than one codon can code for the same amino acid
- Specific: each codon specifies a particular amino acid
- Nonoverlapping & commaless: codons are read one after another without gaps
- Universal: all organisms use the same genetic code
- All 64 codons have meaning; 61 for amino acids and 3 for "stop" signals
- Multiple codons for an amino acid often share common bases
Ribosomes
- Ribosomes are complexes of rRNA and proteins
- Each ribosome has two subunits: a small subunit and a large subunit;
- Small subunit contains one rRNA and 33 proteins
- Large subunit contains 3 rRNA and 49 proteins
- Many ribosomes on one mRNA comprise a polysome with many copies of the protein made simultaneously
Stages of Transcription
- Initiation: RNA polymerase binds to the promoter region of the DNA
- Elongation: RNA polymerase moves along the template strand, synthesizing a complementary RNA molecule
- Termination: RNA polymerase releases the newly formed RNA molecule
Post-Transcriptional Processing
- Prokaryotes release a mature mRNA at the end of termination
- Eukaryotic mRNA is a primary transcript that needs posttranscriptional modification which include
- A 5' cap structure is added
- A 3' poly(A) tail (100-200 adenine nucleotides) is added by poly(A) polymerase
- Required for efficient translation
- Protects from degradation
RNA Splicing
- RNA splicing is the removal of portions (introns) from primary mRNA that are not protein coding
- Bacterial prokaryotic chromosomes are continuous; mRNA contains entire DNA sequence
- Eukaryotic chromosomes are discontinuous, forming introns within the gene sequences that do not code for amino acids
- Spliceosomes, composed of snRNPs and other proteins, recognize intron-exon boundaries and stabilize the splicing complex
Mutations, UV Light, and DNA Repair
- Mutations are mistakes introduced into the DNA sequence of an organism
- Mutations can be silent (no change in the protein sequence) or have negative effects on the organism – Mutagens are chemicals causing changes in DNA; also carcinogens
- UV causes covalent linkage of adjacent pyrimidine bases (thymine dimers)
- Xeroderma pigmentosum is a genetic disorder characterized by increased sensitivity to UV radiation which can cause severe skin-burning and cancer
Type of Mutations
- Point mutations involve a single base substitution. These can be silent, missense, or nonsense.
- Frameshift mutations are due to the insertion or deletion of a base—this shifts the reading frame of the codons, changing all subsequent nucleotides.
Recombinant DNA
- Recombinant DNA is synthetic DNA containing segments from more than one source; it joins two different DNA molecules to create a hybrid.
- This technology is made possible by restriction endonucleases (bacterial enzymes that cut DNA at specific nucleotide sequences) and the enzyme ligase.
- Three key elements in forming recombinant DNA are
- A DNA molecule that will have the new DNA segment.
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Description
Test your understanding of the translation phase in molecular biology with this quiz. Explore key concepts such as elongation, translocation, and termination, along with post-translational modifications and mutations. Perfect for students studying cellular biology or biochemistry.
