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Chapter 17
From gene to protein
| Term | Definition |
|---|---|
| Gene | Segment of DNA whose sequences of nucleotides typically specifies a sequence of amino acids. each chromosome contain 1 long DNA molecule composed of many thousands of genes |
| one gene, one polypeptide (protein) hypothesis | one gene encodes a single protein. there are exceptions. |
| one gene, one polypeptide hypothesis exceptions | sometimes 2 genes code for 2 different polypeptides that interact to make 1 protein. some genes code for RNA molecules and not proteins. Eukaryotic genes can code for more than one protein via alternative splicing. |
| Protein synthesis location | on ribosomes in the cytoplasm. carried out of the nucleus via RNA. |
| RNA structure | usually single stranded. contains the sugar ribose, a phosphate group and a nitrogenous base. contains the bases guanine, adenine, cytosine and uracil. coded for by DNA |
| RNA importance | DNA translation into a protein. |
| Types of RNA | mRNA, rRNA, tRNA |
| Gene Expression | Process by which DNA directs protein or RNA synthesis |
| Transcription | Info contained in DNA is copied into mRNA. Base sequence in mRNA carries info about the amino acid sequence from nucleus to ribosomes. |
| Translation | tRNA and rRNA convert base sequences information in mRNA into a specific amino acid sequences (protein). occurs on ribosomes. |
| Genetic Code | Series of nucleic acids that can be translated into a series of amino acids (proteins). |
| Problem of Genetic Code | Only 4 bases in DNA and 4 RNA, but 20 amino acids |
| Triplet code | 1 base can not code for 1 amino acid so, each amino acid is coded for by a sequence of 3 nucleotides |
| Triplet Codon | 3 mRNA bases that code for an amino acid |
| Start Codon | indicates the beginning of an amino acid (AUG) |
| stop Codon | indicates the end of an amino acid sequence (UAG, UAA, UGA) |
| 60 Codons for 20 amino acids | each amino acid can have 1+ codon. but each codon codes for only 1 amino acid. DNA message is read as a series of non-overlapping 3-letter words and must start at the correct point. |
| Details of Transcription:DNA to RNA | only part of the DNA of a chromosome is transcribed at 1 time. |
| Template strand | Typically, only one of the DNA strand in a helix codes for a protein; used as a template to make complementary RNA strand. But both DNA strands may serve as templates for different proteins |
| Gene regions | Promoter Body Terminator |
| Promotor | short sequence of DNA bases that marks the beginning of a gene; includes a transcription start point |
| Body | DNA bases that code for amino acids in the protein to be synthesized |
| Terminator | signal found at the end of the gene. |
| Transcription steps | Initiation, Elongation, Termination |
| Initiation in bacteria (transcription) | RNA polymerase opens up the DNA strand as a template. transcribed genes are based in conditions inside and outside the cell that signal for protein production. RNA first binds w/ pro motor in a specific orientation. |
| Initiation in Eukaryotes (transcription) | factors bind to promoter 1st then RNA polymerase 2 binds to for a complex; respective sequence containing TATA |
| TATA Box location | in the Promoter |
| During Initiation the DNA unwinds when | RNA polymerase binds with the gene's promotor, changing its shape, forcing the DNA Double Helix to unwind at the beginning of the gene |
| Elongation beginning (transcription) | RNA polymerase travels along template strand using free RNA nucleotides in the nucleus to make a single strand of RNA in a 5' to 3' direction complementary to the template DNA. RNA polymerase untwists the DNA and exposes 10-20 nucleotides at a time. |
| elongation middle (transcription) | After abt 10 nucleotides from the DNA template chain,the chain detaches from the promoter region and the DNA helix reforms. |
| Elongation end(transcription) | As the RNA continues to elongate it forms a long tail that drifts away from the DNA. |
| How many polymerase can RNA transcribe? | many RNA can polymerase can transcribe a single gene simultaneously(move like trucks in a convoy),so large amounts can be made at one time |
| Termination in Bacteria (transcription) | RNA polymerase continues along the template strand until it reaches the termination signal. RNA polymerase detaches from the DNA template strand |
| Termination signal in bacteria (transcription) | Single triggers mRNA transcript to separate from the DNA and RNA polymerase. |
| Termination in Eukaryotes (transcription) | RNA polymerase 2 continues up to 10-35 nucleotides past a polyadenylation single,then proteins cut the mRNA free.RNA polymerase continues along the DNA for a few hundred extra nucleotides, then is released. |
| Polyadenylation single | AAUAAA |
| RNA processing in Eukaryotes (transcription) | mRNA transcript must be altered before translation. |
| RNA processing (eukaryotes) 1ST Step (transcription) | mRNA carries the code for protein amino acid sequence. Pre-mRNA is synthesized in the nucleus, then modified to form functional mRNA |
| RNA processing (eukaryotes) 2nd Step (transcription) | Pre-mRNA is synthesized in the nucleus, then modified to form functional mRNA. |
| RNA processing (eukaryotes) 3rd Step (transcription) | Processed mRNA leaves the nucleus through the nuclear pores and enters the cytoplasm, where it binds to ribosomes |
| Pre-mRNA modification | a nucleotide "5' cap" and "poly-A tail" are added at the ends of the Pre-mRNA |
| Pre-mRNA funcion | facilitate movement of mRNA out of the nucleus.protect mRNA from degeneration by enzymes.Help ribosomes attach to 5' end of mRNA. |
| RNA splicing | Most eukaryotic genes have 1 or more introns |
| Introns | regions of bases that do not get translated into an amino acid sequence |
| exons | regions that do get translated. often longer than introns ** exons exit the nucleus |
| Intron and exon placement | introns are spaced between exons in the mRNA |
| snRNP enzymes | snip out introns and put exons back together before mRNA leaves the nucleus. |
| Different proteins are formed based on: | which pre-mRNA regions are cut out, different proteins may be formed from the same pre-mRNA |
| Due to RNA Splicing | humans can have fewer genes but still make many proteins |
| Introns increase the probability of what? | of cross over between exons which may lead to beneficial new proteins being formed. |
| 3 steps to translation | 1.Intiation 2. Elongation 3. Termination |
| Ribosomes | Composed of 1 large and 1 small subunit which contains proteins and RNAs. the two subunits remain separate unless actively synthesizing proteins. |
| Ribosome binding sites | one for mRNA. three for tRNA |
| Ribosomes and tRNA | A site holds the tRNA carrying the next amino acid to be added to the chain |
| Psite | holds the tRNA carrying the new polypeptide chain. |
| Esite | (exit) where "empty" tRNAs leave |
| Transfer RNA location | Circulate in the cytoplasm |
| tRNA function | binds to free amino acids in the cytoplasm and deliver them to the ribosomes according to the codon sequence of the mRNA. |
| Anticodon | each tRNA carries a specific amino acid and a sequence of 3 nucleotides complementary to the mRNA. |
| Initiation 1st step (translation) | indicator tRNA carries a start anticodon and binds with the small ribosomal subunit |
| Initiation 2nd step (translation) | small subunit binds to mRNA molecule |
| Initiation 3rd step (translation) | indicator tRNA start anticodon binds with mRNA start codon |
| Initiation 4th step (translation) | Large ribosomal subunit attaches to small subunit and binds with initiator and RNA |
| Elongation 1st step (translation) | an assembled ribosome (2 subunits) can encompass 2mRNA codons |
| Elongation 2nd step (translation) | anticodon of a second tRNA recognizes the second mRNA codon and moves to the ribosome |
| Elongation 3rd step (translation) | The large ribosome subunit has a catalytic site that breaks the bond holding the first amino acid to its tRNA and forms a peptide bond between the 2 adjacent amino acids. creates an empty tRNA and a protein of 2AA. |
| the growing chain in elongation | leaves the ribosome and the ribosome moves to the next codon. another tRNA is brought in and its AA is added to the growing chain. |
| Termination 1st step (translation) | near the enf of the mRNA,a stop codon is reached which codes for a release factor. |
| Termination 2nd step (translation) | the release factor cause water to be added to the polypeptide and the completed chain is released from the ribosome through the exit tunnel |
| Termination 3rd step (translation) | typically several ribosomes will attach to the same mRNA |
| Polyribosome | the array of ribosomes that attach to the same mRNA. |
| mRNA formation | RNA nucleotides bind with the template DNA |
| pre-mRNA formation | by eukaryotes is modified to mRNA by splicing |
| Amino acids combination | are linked together following the mRNA sequence to form a ptotein |
| protein modification after translation includes | the addition of sugars, lipids, phosphates. the peptide chain may be cut. 2 or more polypeptides may cut come together to form a protein with quaternary |
| Targeting polypeptides | some polypeptides have a special nucleotide sequence near the beginning called a signal peptide. |
| Recognizing the signal peptide | by special particles in the cytosol that take the ribosome to a protein receptor in the RER. |
| After the signal peptide is recognized | the polypeptide is secreted into the RER. The ribosome detaches from the RER after synthesis is complete. |
| Mutation | change in sequence of DNA bases. occurs when there is a mistake in base-paring during DNA replication. some chemicals and radiation may cause changes in the DNA. can be made during transcription or translation. |
| Faulty genes can cause serious problems because | cell may just have 1 or 2 copies of the gene and may make lots of faulty proteins based on it. |
| Point mutation | change in s single nucleotide pair. sometimes corrected by proofreading enzymes. |
| nucleotide pair substitution | replacement of 1 nucleotide with another pair. example sickle cell anemia |
| insertion mutation (frame shift mutation) | 1 or more extra nucleotide pairs are inserted into a gene; can alter reading frame of the genetic message |
| Deletion mutation (frame shift mutation) | 1 or more nucleotide pairs are removed from a gene |
| translocation | nucleotides are removed from one chromosome and moved to another chromosome |
| wild type | normal not mutated gene |
| Inversion | nucleotides are removed and reinserted in reverse order in the same place |
| Effect of mutations | the protein can remain unchanged. the new protein is equivalent. |
| Silent mutation | even with the presence of a mutation the function of the protein does not change |
| Neutral mutation (missense mutation) | amino acid sequence of the protein may be changed, but overall function remains the same. |
| If the protein function is changed by an altered amino acid sequence result can be | severe illness ex: cystic fibrosis- triplet codon deletion on chromosome 7 |
| if protein function is destroyed by a stop codon | inappropriate stop codon will cut short the translation of mRNA before the protein is finished. could be lethal if protein is important. |
| mutation in gametes | if nonlethal may be passed from generation to generation. |
| Mutations are necessary because | they create evolution and genetic variation. |
| if a beneficial mutation is passed to offspring | that mutation may eventually become common in all organisms of the species. |
Created by:
ejohnson17
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