WEEK 1 (The central dogma) Flashcards
What is the Central dogma of molecular biology?
An explanation of the flow of genetic information within a biological system
What is an essential part of the machinery for synthesising proteins?
RNA-based enzymatic catalysis
What is the “RNA world hypothesis” and what does it propose?
The ability of DNA and RNA to base pair with free nucleotides suggests a scenario in which an RNA sequence spontaneously formed that was then able to self-replicate, ultimately giving rise to many self-propagating copies of itself
This proposes that life began as RNA
What was the importance of Archibald Garrod?
- Provided the first meaningful insight into gene function
- Discovered the relationship between a genetic defect, a specific enzyme and a specific metabolic condition
- One disease investigated was ALCAPTONURIA
Describe Alcaptonuria
A condition where urine becomes dark on exposure to air. Individuals with Alcaptonuria lack an enzyme in their blood that OXIDISED HOMOGENTISIC ACID (a compound formed during the breakdown of PHENYLALANINE and TYROSINE). As homogentisic acid accumulates, it is secreted in the urine and darkens in colour when oxidised in air.
What is the function of Retroviruses?
Retro viruses carry RNA as their genetic information. When they invade their host cell they convert their RNA into a DNA copy using REVERSE TRANSCRIPTASE.
This modifies the central dogma
DNA <-> RNA <-> PROTEIN
Most protein-coding genes occur only once in the genome and are called ____________________
Single-copy genes
What are exons and introns?
Exons = The protein-coding regions of the split genes
Introns = Intervening sequences spliced out before the mRNA leaves the nucleus
What are the four steps for Protein synthesis?
1) Transcription
2) RNA processing
3) Translation
4) Post-translation processing
What is Transcription/RNA synthesis?
The process whereby the information held in the nucleotide sequence of DNA is transferred to RNA
What are genes encoding mRNAs called?
Protein-coding genes
When is a gene said to be expressed?
When its genetic information is transferred to mRNA and then to protein
What are the properties of primary transcripts?
- Do not exist within the cell as naked RNA but become associated with proteins
- Fleeting existence
- Processed into smaller, functional RNAs by a series of “cut and paste” reactions
What is the Primary transcript/Pre-RNA?
The initial precursor RNA equivalent in length to the full length of DNA transcribed
What is the Transcription unit?
The corresponding segment of DNA from which a primary transcript is transcribed
What are the three major types of eukaryotic RNAs?
- Messenger RNA (mRNA) = provides the PLAN for the polypeptide chain
- Ribosomal RNA (rRNA) = provides the PLATFORM for protein synthesis
- Transfer RNA (tRNA) = TRANSLATES the message on the mRNA into a polypeptide chain
Transcription
- Uses RNA polymerase
- Proceeds in the same direction as replication (5’ to 3’)
- Forms a complementary strand of mRNA
- It begins at a PROMOTOR SITE which signals the beginning of a gene
- After end of gene there is a TERMINATOR SEQUENCE that tells RNA polymerase to stop transcribing
In any gene how many DNA strands acts as a template for transcription?
One
What does the sequence of nucleotides in RNA depend on?
The nucleotide sequence in the DNA template
Which enzyme is used to transcribe DNA into RNA?
RNA Polymerase
What is the role of RNA Polymerase in Transcription?
- Recognises the beginning of the gene to be transcribed
- Catalyse the formation of phosphodiester bonds between the nucleotides that have been selected according to the sequence within the DNA template
What is the functions of DNA-dependent RNA Polymerases?
- Search DNA for initiation site
- Unwinds a short stretch of double helical DNA to produce a single-stranded DNA template
- Selects the correct ribonucleotide and catalyses the formation of a phosphodiester bond
- Detects termination signals where transcript ends
What is the Promoter?
The site on the DNA to which an RNA Polymerase molecule binds prior to initiating transcription
What is the importance of Transcription factors?
Helps cellular RNA Polymerases to recognise promoters since they cannot on their own
What is the significance of the Promoter?
- Provides a binding site for Polymerase
- Contains the information that determines which of the two DNA strands is transcribe and the site at which transcription begins
What is a Transcription bubble?
A molecular structure formed during DNA transcription when a limited portion of the DNA double strand is unwound