week 3 Flashcards
what is the central dogma?
the flow of information: DNA -> RNA -> protein
how is RNA synthesised?
RNA is synthesized via a process called Transcription
how are RNA and DNA different?
- RNA is single-stranded (but it can fold back upon itself to form secondary structure, e.g. tRNA)
- In RNA, the sugar molecule is ribose rather than deoxyribose
- In RNA, the fourth base is uracil rather than thymine.
what type of structures can RNA form?
RNA can form 2 degree and 3 degree structures
RNA is single-stranded but it can fold back upon itself to form secondary structures (tRNA)
What defines the polarity of the DNA double helix?
The polarity of the DNA double helix is defined by the orientation of the 5’ to 3’ ends of each strand, which is determined by the presence of a 5’-phosphate (PO4) group at the 5’ end and a 3’-hydroxyl (OH) group at the 3’ end.
Flashcard 2:
How is RNA structurally different from DNA in terms of polarity and strand number?
RNA is typically single-stranded as opposed to the double-stranded structure of DNA, yet it still maintains a 5’ to 3’ polarity. RNA strands often fold into complex three-dimensional shapes due to intramolecular base pairing.
How do the structural features of DNA and RNA relate to their functions?
The antiparallel and complementary strands of DNA create a stable template for replication and transcription. RNA’s structure allows it to perform various functions, including coding, decoding, regulation, and expression of genes. RNA’s ability to fold into complex shapes enables it to catalyze biological reactions, regulate gene expression, and act as a messenger between DNA and ribosomes in protein synthesis.
What are the three phases of transcription?
The three phases of transcription are initiation, in which the RNA polymerase binds to the promoter sequence of DNA; elongation, where the RNA strand is synthesized; and termination, where the RNA synthesis is concluded and the RNA molecule is released.
How does initiation of transcription occur and what is the role of the promoter?
During initiation, the enzyme RNA polymerase recognizes and binds to a specific sequence of DNA known as the promoter. The promoter indicates the starting point for transcription and specifies which of the two DNA strands should be transcribed. It also includes the initiation site where transcription begins.
What happens during the elongation phase of transcription?
n the elongation phase, RNA polymerase synthesizes the RNA molecule in a 5’ to 3’ direction, antiparallel to the DNA template strand. Nucleotides are added based on complementary base pairing with the template DNA. Energy for this process comes from the hydrolysis of ribonucleoside triphosphates. The growing RNA strand has a sequence identical to the DNA coding strand (except for uracil replacing thymine) and complementary to the template strand.
How is transcription terminated and what happens to the primary transcript?
Transcription is terminated when RNA polymerase encounters special DNA sequences and protein factors that signal the end of the RNA transcript. The RNA transcript, known as pre-mRNA, is then released from the DNA. This primary transcript undergoes processing, including splicing, capping, and polyadenylation, to form the mature mRNA, which can be exported from the nucleus for translation.
What is the genetic code and how is it structured in terms of codons?
The genetic code is a set of rules that defines how a sequence of nucleotides (codons), each consisting of three bases (A, C, G, T), is translated into proteins. With four different bases, there are 64 possible codons. These codons encode one start codon for methionine, three stop codons to terminate translation, and 60 codons that specify the 20 amino acids. The code is redundant, with several codons coding for the same amino acid, yet specific, as one codon does not code for more than one amino acid. The genetic code is almost universally conserved across organisms.
How does translation differ between prokaryotes and eukaryotes, and what components are required for translation?
In prokaryotes, translation can begin before the synthesis of mRNA is complete. In contrast, eukaryotes perform transcription in the nucleus and translation in the cytoplasm. Translation requires four key components: ribosomes (the site of protein synthesis), transfer RNAs (tRNAs that bring amino acids to the ribosome), activating enzymes (to attach amino acids to tRNA), and the mRNA molecule, which serves as the template for protein synthesis.
What is the structure and function of transfer RNA (tRNA) in protein synthesis?
tRNA molecules have a three-dimensional cloverleaf structure with an anticodon loop that recognizes specific codons on mRNA and an amino acid attachment site at the 3’ end, which is always the nucleotide sequence CCA. tRNA molecules are key adapters that translate the genetic information from mRNA into the amino acid sequence of proteins.
How does tRNA contribute to the specificity of amino acid selection during translation?
Each tRNA molecule has a specific anticodon that base-pairs with a complementary codon on the mRNA strand. This ensures that tRNAs bring the correct amino acid corresponding to each mRNA codon during protein synthesis. The hydrogen bonds between the paired bases allow the tRNA to maintain its three-dimensional structure.
