Chapter 10: Gene Expression Flashcards
Central Dogma of Molecular Biology
It describes the flow of heritable information by showing the replication of DNA goes through transcription to RNA and then gets translated to proteins (amino acids)
What is Molecular Biology
It is the study of nucleic acids and proteins, and it often focuses on gene expression
What happens during transcription?
The information in a DNA sequence (a gene) is copied into a complementary RNA sequence ( A,C,G,U)
What happens during Translation?
This RNA sequence is used to create the amino acid sequence of a polypeptide and is the process of creating proteins from an mRNA template
Heredity
Is the transmission of DNA (RNA in many viruses) from an organism to its progeny (decedents)
Chromosomes
Are large molecules of DNA containing genes: circular in Prokaryotes and linear in eukaryotes
Genes
Are sequences of DNA that forms a functional unit on a chromosome and encodes for a protein or a functional RNA
Locus/Loci
Are the physical location of a gene on a chromosome
RNA Polymerase
Is a protein complex that builds RNA out of the ribonucleic tide
What are the three types of RNA in protein synthesis?
- Messenger RNA (mRNA) and transcription
- Ribosomal RNA (rRNA) and translation
- Transfer RNA mediates between mRNA and protein
Messenger RNA (mRNA)
carries the genetic information copied from DNA in the form of a series of three-base code “words,” each of which specifies a particular amino acid
Ribosome
Is essentially a protein synthesis factory with multiple proteins
Ribosomal RNA (rRNA)
associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains.
Transfer RNA (tRNA)
is the key to deciphering the code words in mRNA. Each type of amino acid has its own type of tRNA, which binds it and carries it to the growing end of a polypeptide chain if the next code word on mRNA calls for it.
What are the three steps of Transcription?
- Initiation
- Elongation
- Termination
Promoter
Is a special DNA sequence to which the RNA polymerase binds very tightly. They are control sequences that “tell” the RNA polymerase where to start transcription and which of the two DNA strands to transcribe
What direction does transcription begin?
It goes from the 5’ to 3’ direction in which the 5’ is the coding strand and the 3’ on the template strand
Elongation
This is where RNA nucleotides supply appropriate nitrogenous base pairings. For example, if the DNA sequence consists of the bases adenine, thymine, guanine, adenine, cytosine, thymine (TGACT)
Initiation
RNA polymerase (an enzyme) attaches to a ‘promotor’ sequence which indicates the start of the section of gene that is to be copied. Bound to the promotor, RNA polymerase severs the weak hydrogen bonds between each nitrogenous base pair and essentially unzips the double DNA strand
Termination
is the end of the process. Guided by a terminator sequence on the DNA, the strand of newly manufactured RNA detaches from the DNA.
Coding Regions
Are sequences within a DNA molecule that are eventually translated as proteins
Introns
Introns are noncoding sequences that interrupt the coding region. They are removed by the time the mature mRNA leaves the nucleus
Exons
Exons are made up of stretches of DNA that will ultimately be translated into amino acids and proteins. In the DNA of eukaryotic organisms, exons can be together in a continuous gene or separated by introns in a discontinuous gene
Pre-mRNA (precursor RNA)
When the gene is transcribed into pre-mRNA the transcript contains both introns and exons and the pre-mRNA is then processed and the introns are spliced out of the molecule
RNA Splicing
It removes the introns and splices the exons together by spliceosomes that are made of 5 nuclear RNAs and 80 proteins
What are the modification at both ends of pre-mRNA?
- A 5’ Cap
2. A poly A tail
What is a 5’ Cap?
It’s a chemically modified molecule of guanosine triphosphate (GTP) and facilitates the binding of mRNA to the ribosome for translation and protects the mRNA from being eaten by ribonucleases
What is a Poly A tail?
It is added to the 3’ end at the end of transcription and assists in export from the nucleus and aids stability
What is a Poly A tail?
It is added to the 3’ end at the end of transcription and assists in export from the nucleus and aids stability
Start Codon
The start codon is AUG which is Methionine
Stop Codons
Stop codons are used to terminate signals for translation. The three stop codons are UAA UAG and UGA
Point Mutation
Are changes in single nucleotides within a sequence
What are the types of point mutations?
- silent mutations (doesn’t cause any change in aa sequence
- Missense mutations (change in amino acids)
- Nonsense Mutation (premature stops a codon
- Frame-shift mutations (inserting/deleting one or more base pairs)
What are the three functions of tRNA?
- tRNAs bind to particular amino acids (specific)
- tRNAs bind to mRNA
- tRNAs interact with ribosomes
Where does Translation occur?
It occurs at the ribosome, which is the molecular workbench where the translation of mRNA by tRNA is accomplished
On a large subunit of the ribosome, where are the three sites to which a tRNA can bind to?
- The A (amino acid) site
- The P (polypeptide) Site
- The E (exit) site
What are the three steps of Translation?
- Initiation (Initiation complex)
- Elongation
- Termination
Initiation Complex of translation?
It consists of a charged tRNA and a small ribosomal subunit, both bound to the mRNA
Elongation of translation?
Where a charged tRNA whose anticodon is complementary to the second codon of the mRNA now enters the open A site of the large ribosomal subunit and catalyzes two reactions
What are the two reactions of the large ribosomal subunit?
- It breaks the bond between the methionine and its tRNA in the P site
- It catalyzes the formation of a peptide bond between methionine and the amino acid attached to the tRNA in the A site
