From DNA to Protein Flashcards
Describe the key features of the RNA.
RNA is a single-stranded nucleic acid made of ribonucleotides, each composed of a ribose sugar, a phosphate group, and a nitrogenous base (A, U, C, or G). RNA can form complex 3D structures with double-stranded regions and loops.
Describe at least 4 different types of RNA and their role in the cell.
There are many types of RNA in the cell, each with a specific function. Some examples are:
mRNA: messenger RNA, carries the genetic information from DNA to the ribosome for translation into protein.
tRNA: transfer RNA, binds to a specific amino acid and recognizes the corresponding codon on the mRNA during translation1.
rRNA: ribosomal RNA, forms the core of the ribosome and catalyzes the peptide bond formation between amino acids.
snRNA: small nuclear RNA, participates in the splicing of pre-mRNA in the nucleus.
What are the main differences between the DNA and the RNA
DNA and RNA are both nucleic acids, but they differ in several aspects, such as:
Sugar: DNA has deoxyribose, while RNA has ribose. Deoxyribose lacks an oxygen atom on the 2’ carbon of the sugar ring.
Base: DNA has thymine (T), while RNA has uracil (U). Thymine and uracil are both pyrimidines and can pair with adenine (A).
Strand: DNA is usually double-stranded, forming a double helix with complementary base pairing. RNA is usually single-stranded, but can fold into complex structures with internal base pairing2.
Stability: DNA is more stable than RNA, due to the absence of the 2’ hydroxyl group and the presence of thymine. RNA is more prone to degradation by enzymes and chemical reactions.
Function: DNA stores the genetic information of the cell and is replicated during cell division. RNA acts as an intermediary between DNA and protein, and performs various regulatory and catalytic roles in the cell.
Describe the key feature of the amino acids.
Amino acids are the building blocks of proteins. They have a central carbon atom attached to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain ®3. There are 20 different amino acids, each with a different side chain that determines its chemical properties and interactions.
What is the central dogma?
The central dogma is the concept that describes the flow of genetic information in the cell, from DNA to RNA to protein4. It was proposed by Francis Crick in 1957 and states that “within each cell, the genetic information flows from DNA to RNA to protein. Once into proteins, it cannot get out again”.
How is RNA transcribed? Describe the key steps of transcription
Initiation: The RNA polymerase binds to a promoter,
RNA polymerase starts RNA synthesis in the 5’ to 3’ direction
Elongation: RNA polymerase moves along the DNA, unwinding it and adding nucleotides to the growing RNA strand.
The RNA strand is displaced from the DNA and the DNA helix reforms behind the transcription bubble.
Termination: The RNA polymerase reaches a termination signal. The RNA polymerase and the RNA transcript are released from the DNA.
How are the protein translated? Describe the key steps of translation
Initiation: The small ribosomal subunit binds to the 5’ end of the mRNA and scans for the start codon (AUG), which codes for methionine.
A tRNA with the anticodon UAC and the amino acid methionine binds to the start codon. The large ribosomal subunit joins the complex, forming the initiation complex.
The tRNA occupies the P site of the ribosome, while the A site is ready for the next tRNA.
Elongation: The ribosome moves along the mRNA, reading the codons and bringing the corresponding tRNAs with their amino acids.
A peptide bond is formed between the amino acid in the P site and the amino acid in the A site, transferring the growing polypeptide chain to the A site.
The tRNA in the P site moves to the E site and is ejected.
The tRNA in the A site moves to the P site.
The A site is vacant for the next tRNA.
This cycle repeats until the ribosome reaches a stop codon.
Termination: The ribosome encounters a stop codon (UAA, UAG, or UGA), which does not have a matching tRNA.
A release factor binds to the stop codon and triggers the hydrolysis of the polypeptide chain from the tRNA in the P site.
The ribosome dissociates into its subunits and the mRNA and the polypeptide are released.
What are the t-RNAs? How are they synthetized? Why are they relevant in translation?
tRNAs are small non-coding RNAs that act as adapters between the mRNA and the amino acids. They have a cloverleaf structure with an anticodon loop that recognizes the codon on the mRNA and an acceptor stem that carries the corresponding amino acid10. They are synthesized by RNA polymerase III in the nucleus and processed by various enzymes that modify some of their bases and attach the amino acid. They are relevant in translation because they ensure the correct and efficient incorporation of the amino acids into the polypeptide chain, according to the genetic code.
What does it mean that the genetic code is redundant?
The genetic code is redundant, meaning that some amino acids are encoded by more than one codon11. For example, leucine is encoded by six codons: UUA, UUG, CUU, CUC, CUA, and CUG. This redundancy allows for some flexibility and tolerance in the translation process, as some mutations in the codons may not change the amino acid and thus the protein function.
What is wobble base pair? Why is it relevant?
Wobble base pair is a phenomenon that occurs in the third position of the codon-anticodon interaction, where some non-standard base pairs are allowed. For example, guanine (G) can pair with uracil (U) or inosine (I), which is a modified base derived from adenine (A). This allows for some tRNAs to recognize more than one codon, reducing the number of tRNAs needed for translation. Wobble base pair is relevant because it increases the efficiency and accuracy of translation, as it reduces the chance of errors and mismatches.
Which are the main components of the ribosome?
The ribosome is a complex molecular machine that catalyzes the translation of mRNA into protein. It is composed of two subunits, the large and the small, which are made of more than 50 proteins and several ribosomal RNAs (rRNAs)12. The large subunit (60S in eukaryotes) contains three rRNAs (28S, 5.8S, and 5S) and about 45 proteins. The small subunit (40S in eukaryotes) contains one rRNA (18S) and about 33 proteins. The rRNAs form the core of the ribosome and are responsible for the peptidyl transferase activity and the decoding of the mRNA. The proteins stabilize the structure and facilitate the interactions with the mRNA and the tRNAs.
What is a frameshift mutation? What in the DNA sequence can cause it?
A frameshift mutation is a type of small-scale mutation that occurs when one or more nucleotides are inserted or deleted from the DNA sequence, causing a shift in the reading frame of the codons. This results in a completely different amino acid sequence downstream of the mutation site, often leading to a premature stop codon and a truncated protein. A frameshift mutation can be caused by errors in DNA replication, recombination, or repair, or by external agents such as chemicals or radiation.
What is the difference between small scale and large scale mutations? Make an example
each.
Small-scale mutations are mutations that affect one or a few nucleotides in a gene, such as substitutions, insertions, or deletions13. They can alter the amino acid sequence and the function of the protein encoded by the gene. For example, a substitution mutation in the gene for hemoglobin causes sickle cell anemia, a blood disorder. Large-scale mutations are mutations that affect a large part of a chromosome or the whole chromosome, such as inversions, duplications, deletions, translocations, or aneuploidy14. They can alter the number, structure, and expression of the genes on the chromosome. For example, a deletion mutation in chromosome 5 causes Cri du chat syndrome, a developmental disorder.
Describe four different kinds of chromosome mutations
Chromosome mutations are mutations that affect the structure or the number of the chromosomes in a cell. Some examples are:
Inversion: A segment of a chromosome is reversed in orientation, changing the order of the genes.
Deletion: A segment of a chromosome is lost, removing some genes.
Duplication: A segment of a chromosome is copied and inserted, creating extra copies of some genes.
Translocation: A segment of a chromosome is exchanged with a segment of another chromosome, creating new gene combinations.
Aneuploidy: A whole chromosome is gained or lost, changing the number of chromosomes in a cell.
