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Chapter 14: Gene Expression From Gene to Protein
Terms in this set (32)
What is a reading frame?
- A reading frame is a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets.
- Once a gene has been sequenced, it is important to determine the correct open reading frame (ORF). Every region of DNA has six possible reading frames, three in each direction.
- The reading frame that is used determines which amino acids will be encoded by a gene.
How does information flow from gene to protein?
The sequence of nucleotides in DNA holds the instructions for making proteins but must first be transcribed into RNA nucleotides. RNA then takes the message out of the nucleus to the ribosomes, the site of protein synthesis. At the ribosomes, RNA is translated into amino acids to form a polypeptide that later folds to become a protein.
Whats the difference between transcription and translation?
Transcription is the copying of DNA nucleotides to RNA nucleotides. Translation is the conversion of RNA nucleotides (codons) into amino acids.
Describe function and structure of ribosomes.
- Ribosomes facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis.
- RIbosome is made up of two subunits; large and small subunits
- Each ribosome has three binding sites of tRNA
- P site: holds the tRNA carrying the growing polypeptide chain
- A site: holds the tRNA carrying the next amino acid to be added to the chain
- E site: is where the discharged tRNAs leave the ribosome
Explain why sex-linked diseases are more common in human males.
- Since males have only one locus, the terms homozygous and heterozygous lack meaning for describing their sex-linked genes; the term hemizygous is used in such cases. Any male receiving the recessive allele from his mother will express the trait.
Where does transcription and translation occur in prokaryotes and eukaryotes?
Transcription occurs in the nucleus and mRNA is transported to the cytoplasm, where translation occurs.
Compare protein synthesis in prokaryotes and eukaryotes?
Eukaryotic DNA has sections called introns that don't code for anything. They are transcribed into mRNA, but they must be removed from mRNA before translation can occur. This is accomplished by complexes of snRNPs, or small nuclear ribonucleoproteins. The mRNA therefore has to undergo processing before it can be translated.
Prokaryotic DNA lacks introns, so mRNA can be translated
after transcription. Ribosomes often line up along a strand of mRNA to being translating it, much like beads on a string, even while the mRNA is still being transcribed. That rapid-fire change from gene to mRNA to protein could never happen in eukaryotes.
During the act of translation itself, eukaryotes use ribosomes that are slightly larger and more complex than prokaryotic ribosomes. Each type of ribosome has a sedimentation number which describes when and where it settles in a centrifuge. Eukaryotic ribosomes are 80S while prokaryotic ribosomes are only 70S.
What is gene?
Gene is the sequence of nucleotides in DNA encoding for one mRNA molecule or one polypeptide chain.
What is the structure of a gene?
- Eukaryotic gene structure: most eukaryotic gene in contrast to typical bacterial genes, the coding sequence (exons) are interrupted by noncoding DNA (introns)
- Gene must have (exon; start signals; stop signals; regulatory control elements)
What is a promoter?
In genetics, a promoter is a region of DNA that initiates transcription of a particular gene. Promoters are located near the transcription start sites of genes, on the same strand and upstream on the DNA (towards the 5' region of the sense strand).
What is a transcription unit?
A transcription unit is the distance between sites of initiation and termination by RNA polymerase; may include more than one gene.
What is the process of mRNA that occurs that occurs in Eukaryotes?
Enzymes modify the two ends of a eukaryotic pre-mRNA molecule. The modified ends promote export of mRNA from nucleus , and they help to protect the mRNA from degradation. When mRNA reaches cytoplasm, the modified ends, in conjunction with certain cytoplasmic proteins, facilitate ribosome attachment. The 5' cap and poly-A tail are not translated into protein, nor are the regions called the 5' untranslated region and 3 untranslated region.
What types of RNA are there?
There are 4 types of RNA, each encoded by its own type of gene: mRNA - Messenger RNA: Encodes amino acid sequence of a polypeptide. tRNA - Transfer RNA: Brings amino acids to ribosomes during translation. rRNA - Ribosomal RNA: With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA.
What function do modifications have?
What are the differences between introns and exons?
INtrons stay IN the Nucleus (to keep the DNA safe) and EXons EXit the nucleus to be made into a protein. During RNA processing (after Transcription) introns are spliced out while the Exons remain and go to the ribosome to make a protein. Other parts of RNA processing include the addition of a Poly-A Tail to the 3' end and a guanine cap to the 5' end.
What is splicing?
Removal of Introns
What determines the primary structure of a protein?
The primary structure for protein is made of amino acids, called a polypeptide.
Each amino acid has an R group which is arranged in a long sequence when linked with other amino acids, to form the polypeptide aka primary structure of protein.
What happens to a polypeptide/protein after its amino acids are assembled?
What determines whether a ribosome will be free in the cytosol or attached to the rough ER?
Membrane-bound ribosomes make endomembrane and secreted proteins
Amino-terminal signal peptide is bound by signal-peptide recognition particle
Complex binds to rough ER
Signal peptide is removed from finished protein
What are point mutations?
Changes in a single nucleotide pair of a gene.
What is a base-pair substitution?
- The replacement of one nucleotide and its partner with another pair of nucleotides.
- Some substitution have no effect on the encoded protein, owing to the redundancy of the genetic code.
Ex: if 3' CCG 5' mutated to 3' CCA 5' the mRNA codon used to be GGC would become GGU, but glycine would still be inserted at proper location in protein.
What is a base- pair insertion?
Addition of nucleotide pairs in a gene.
What are mutagens? How do they cause mutations?
Changes that are responsible for the huge diversity of genes found among organisms because mutations are the ultimate source of new genes.
What is the genetic code? What's unambiguous about it?
- Encoding DNA.
- The language of A C G and U
- Groups of three bases form codons, and each codon stands for one amino acid (or start or stop). The codons are read in sequence following the start codon until a stop codon is reached. The genetic code is universal, unambiguous, and redundant.
- Redundant: Some amino acids can be specified by more than one codon.
- Unambiguous: Each codon specifies a particular amino acid and only that amino acid.
Why is Methionine (AUG) special?
It functions as a "START" signal for ribosomes to begin translating the mRNA at that point.
What does the STOP codon signal?
"STOP" codon marks where ribosomes end translation
What are the consequences for alterations in chromosome number?
What are the consequences for alterations in inversions?
What are the consequences for alterations in translocation?
What are the consequences for alterations in duplications?
What are the consequences for alterations in deletions?
Explain the reasoning that led scientists to connect genes and phenotypes to proteins and enzymes? How has this concept changed over time?
Garrod was an MD
Focused on rare and unusual birth defects; inborn errors of metabolism
Urine turns black; contains alkapton
Hypothesized a missing enzyme for brealing down alkapton
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