| 489322113 | Gibberellins | A growth hormone that stimulates normal elongation of stems.
What Mendel's dwarf peas lacked. | |
| 489322114 | One Gene-One Polypeptide Hypothesis | Began as the One Gene-One Enzyme Hypothesis which states that the function of a gene is to dictate the production of a specific enzyme.
It was then realized that proteins are in fact gene products and not always enzymes. Moreover, proteins are constructed from two or more different polypeptide chains, and each polypeptide i specified by its own gene, so the hypothesis turned into this.
Not completely accurate though since genes can code for RNA molecules as well. | |
| 489322115 | RNA | Chemically similar to DNA but contains ribose instead of deoxyribose as its sugar and has nitrogenous base uracil (U) rather than thymine (T) and thus each nucleotide along its strand has A, G, C, or U as its base.
Usually a single strand.
Synthesized in an antiparallel direction to the template strand of DNA, from 5' to 3'. | |
| 489322116 | Stages of DNA to Protein | Two stages: transcription and translation. | |
| 489322117 | Transcription | First stage of getting from DNA to protein.
The synthesis of RNA under the direction of DNA; the information is simply transcribed, or copied, from one molecule to the other.
Just as a DNA strand provides a template for the synthesis of a new complimentary strand during DNA replication, it provides a template for assembling a sequence of RNA nucleotides.
The resulting RNA molecule is a faithful transcript of the gene's protein-building instructions. | |
| 489322118 | Messenger RNA (mRNA) | Type of RNA molecule that carries a genetic message from the DNA to the protein-synthesizing machinery of the cell. | |
| 489322119 | Translation | The actual synthesis (following transcription) of a polypeptide, which occurs under the direction of mRNA.
The cell must translate the base sequence of an mRNA molecule into the amino acid sequence of a polypeptide.
The site of translation are ribosomes.
A polypeptide is always synthesized in one direction, from the initial methionine at the amino acid end (N-terminus) toward the final amino acid at the carboxyl end (C-terminus). | |
| 489322120 | Ribosomes (definition) | Complex particles that facilitate the orderly linking of amino acids into polypeptide chains.
Facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis.
In eukaryotes, the subunits are made in the nucleus: rRNA genes on the chromosomal DNA are transcribed, and the RNA is processed and assembled with proteins imported from the cytoplasm. The resulting ribosomal subunits are then exported via nuclear pores to the cytoplasm. | |
| 489322121 | Differences in Transcription/Translation in Pro and Eukaryotes | Because bacteria lack nuclei, their DNA is not segregated from ribosomes and the other protein-synthesizing equipment, allowing translation of an mRNA to begin while its transcription is still in progress. In contrast, the eukaryotic cell has a nucleus which separates transcription from translation but before they can leave the nucleus, eukaryotic RNA transcripts are also modified in various ways to produce the final, functional mRNA. | |
| 489322122 | RNA Processing | Process that yields the finished mRNA in the eukaryotic nucleus after transcription of a protein-coding eukaryotic gene results in pre-mRNA. | |
| 489322123 | Primary Transcript | The general name for the initial RNA transcript from any gene, including those coding for RNA that is not translated into protein. | |
| 489322124 | Triplet Code | The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three-nucleotide words.
Triplets of nucleotide bases are the smallest units of uniform length that can code for all the amino acids. | |
| 489322125 | Template Strand | The strand of DNA that is transcribed since it provides template for ordering the sequence of nucleotides in an RNA transcript.
For each gene, only one of the two strands is transcribed.
A given DNA strand can be the template strand for some genes along a DNA molecule, while for other genes in other regions, the complementary strand may function as the template. | |
| 489322126 | Codons | mRNA base triplets.
Customarily written in the 5' to 3' direction.
During translation, the sequence of codons along an mRNA molecule is decoded, or translated, into a sequence of amino acids making up a polypeptide chain.
They are read in the translation machine in the 5' to 3' direction along the mRNA. | |
| 489322127 | Termination Codons | Or stop signals.
Mark the end of translation.
UAA, UGA, and UAG are all termination codons. | |
| 489322128 | Initiation Codon | Or start signal.
Marks where translation should begin.
AUG is a start codon and codes for the amino acid methionine (Met)--as a result, polypeptide chains begin with Met when they are synthesized but an enzyme may come and remove this started amino acid from the chain. | |
| 489322129 | RNA Polymerase | An enzyme that pries the two strands of DNA apart and hooks together the RNA nucleotides as they base-pair along the DNA template.
Can only assemble a polynucleotide in its 5' to 3' direction.
No primer is needed for it to begin.
Bacteria have a single type that synthesizes not only mRNA but also other types of RNA that function in protein synthesis.
Eukaryotes though have 3 types in their nuclei, numbered I, II, and II. The one used for mRNA synthesis is RNA polymerase II while he other two transcribe RNA molecules that are not translated into protein. | |
| 489322130 | Promoter | The DNA sequence where RNA polymerase attaches and initiates transcription.
A crucial promoter DNA sequence is the TATA box in eukaryotes.
Prokaryotic RNA polymerase specifically recognized and binds the promotor by itself. | |
| 489322131 | Terminator | The sequence that signals the end of transcription in prokaryotes. | |
| 489322132 | Transcription Unit | The stretch of DNA that is transcribed into an RNA molecule. | |
| 489322133 | The 3 Stages of Transcription | Initiation, elongation, and termination. | |
| 489322134 | Transcription Factors | In eukaryotes, a collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.
Only after certain transcription factors are attached to the promoter does RNA polymerase II bind to it. | |
| 489322135 | Transcription Initiation Complex | The completed assembly of transcription factors and RNA polymerase II bound to the promote on a DNA molecule.
Crucial for the initiation of transcription. | |
| 489322136 | TATA Box | A crucial promoter DNA sequence in forming the initiation complex in eukaryote. | |
| 489322137 | Termination of Transcription | In prokaryotes, transcription proceeds through a terminator sequence in the DNA. The transcribed terminator (an RNA sequence) functions as the termination signal, causing the polymerase to detach from the DNA and release the transcript, which is available for immediate use as mRNA.
In eukaryotes, however, the pre-mRNA is cleaved from the growing RNA chain while RNA polymerase II continues to transcribe the DNA. The polymerase transcribes a sequence on the DNA called the polyadenylation signal sequence which codes for a
polyadenylation signal (AAUAAA) in the pre-mRNA. Proteins associated with the growing mRNA strand cut it free from the polymerase a couple nucleotides downstream from the AAUAAA signal, releasing the pre-mRNA. Polymerase continues transcribing though until it falls off the DNA. The pre-mRNA is then modified during RNA processing. | |
| 489322138 | Alterations Done to Pre-mRNA | The 5' end (transcribed first) is capped off with a modified form of guanine (G) nucleotide after transcription of the first 20 to 40 nucleotides, forming a 5' cap.
The 3' end gets 50-250 adenine (A) nucleotides added to it, forming the poly-A tail.
There are also untranslated regions of the RNA (UTRs) found on the inner sides of the 5' cap and poly-A tail. They have functions such as helping in ribosome binding.
The alterations help by facilitating the export of the mature mRNA from the nucleus, helping protect the mRNA from degradation by hydrolytic enzymes, and helping the ribosomes attach to the 5' end of the mRNA once in the cytoplasm. | |
| 489322139 | 5' Cap | The modified 5' end of pre-mRNA where a modified form of guanine (G) nucleotide is placed after for the first 20-40 nucleotides are transcribed.
Facilitates the export of the mature mRNA from the nucleus, helps protect the mRNA from degradation by hydrolytic enzymes, and helps the ribosomes attach to the 5' end of the mRNA once in the cytoplasm. | |
| 489322140 | Poly-A Tail | The modified tail of the 3' end of pre-mRNA before it is release out of the nucleus.
Is altered by the addition of 50-250 adenine (A) nucleotides to it.
Facilitates the export of the mature mRNA from the nucleus, helps protect the mRNA from degradation by hydrolytic enzymes, and helps the ribosomes attach to the 5' end of the mRNA once in the cytoplasm. | |
| 489322141 | RNA splicing | The removal of a large portion of the RNA molecule that is initially synthesized since most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides, regions that will not be translated.
The introns are cut out from the RNA molecule while the exons are joined together, forming an mRNA molecule with a continuous coding sequence. | |
| 489322142 | Introns | The noncoding segments of nucleic acid that lie between coding regions.
Also known as the intervening sequences. | |
| 489322143 | Exons | The regions of nucleic acid that will eventually be expressed by being translated into amino acid sequences. | |
| 489322144 | How RNA Splicing is Carried Out | A signal for RNA splicing is a short nucleotide sequence at each end of an intron and is recognized by snRNPs. | |
| 489322145 | snRNP | Or small nuclear ribonucleoproteins.
Recognize the sequences at the end of introns which signal splicing.
Located in cell nucleus and are composed of RNA (specifically snRNA) and protein molecules. | |
| 489322146 | snRNA | Or small nuclear RNA.
The RNA found in snRNPs.
About 150 nucleotides long and several join with additional proteins to form an even larger assembly called a spliceosome. | |
| 489322147 | Spliceosome | Made up of assembled snRNA (which locate the sequence at the end of introns that signal splicing) and protein molecules.
About the size of a ribosome.
Interacts with certain sites along an intro, releasing the intron and joining together the two exons that flanked the intron. | |
| 489322148 | Ribozymes | RNA molecules that function as enzymes.
In a type of protozoan (and some other organisms), the intro RNA molecules functions as ribozymes and catalyze their own excision. Self-splicing occurs in the production of ribosomal RNA (rRNA); the pre-rRNA actually removes its own introns. | |
| 489322149 | Alternative Splicing | A process by which the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing. The resulting different mRNAs may be translated into different protein isoforms; thus, a single gene may code for multiple proteins. | |
| 489322150 | Transfer RNA (tRNA) Function | Interprets the message from a series of codons along an mRNA molecule during translation.
Transfers amino acids from the cytoplasmic pool of amino acids to a ribosome.
As a tRNA molecule arrives at a ribosome, it bears a specific amino acid at one end; at the other end is a nucleotide triplet called an anticodon, which base-pairs with a complementary codon on mRNA.
Is a translator because it can read a nucleic acid word (the mRNA codon) and interpret it as a protein word (the amino acid).
In eukaryote, it is made in the nucleus and must travel from the nucleus to the cytoplasm, where translation occurs.
In both eu and prokaryotes, the tRNA is used repeatedly, picking up its designated amino acid in the cytosol, depositing its cargo at the ribosome, and then leaving the ribosome to pick up another amino acid. | |
| 489322151 | Anticodon | One end of a tRNA molecule that base-pairs with a complementary codon on mRNA; a specific amino acid is found on the other end.
A nucleotide triplet. | |
| 489322152 | tRNA Structure | Consists of a single RNA strand that is only about 80 nucleotides long.
Has complementary stretches of bases that can hydrogen-bond to each other, allowing the single strand to fold back upon itself, forming a molecule with a 3D structure.
Folds roughly into an L shape.
The loop protruding from one end of the L includes the anticodon, the special base triplet that binds to a specific mRNA codon. | |
| 489322153 | Aminoacyl-tRNA synthetase | An enzyme that joins the correct tRNA to the correct amino acid.
The active site of each type fits only a specific combination of amino acid and tRNA.
There are 20 different types, one for each amino acid.
Catalyzes the covalent attachment of the amino acid to its tRNA in a process driven by hydrolysis of ATP. | |
| 489322154 | Wobble | The relaxation of the base-pairing rules seen in the tRN anticodon and mRNA codon matching.
There are 45 tRNAs which means that some must be able to bind to more than one codon: versatility in the base pairing between the third base of a codon and the corresponding base of a tRNA anticodon are not as strict as those for DNA and mRNA codons.
(e.g. the base U at the 5' end of a tRNA anticodon can pair with either A or G in the third position of an mRNA codon). | |
| 489322155 | Ribosome (form) | Made up of two subunits, called the large and small subunits--they are each constructed of proteins and RNA molecules called ribosomal RNA, or rRNA.
In both pro and eukaryotes, the large and small subunits join to form a functional ribosome only when they attach to an mRNA molecule.
In addition to the binding site for mRNA, each has 3 binding sites for tRNA: the P site, the A site and the E site.
The ribosome holds the tRNA and mRNA in close proximity and positions the new amino acid for addition to the carboxyl end of the growing polypeptide. It then catalyzes the formation of the peptide bond. When complete, the polypeptide is released to the cytosol through the exit tunnel. | |
| 489322156 | rRNA | Ribosomal RNA.
Together with proteins, make up a ribosome. | |
| 489322157 | P site | One of the three binding sites for tRNA on the ribosome--located between the A and E sites.
Holds the tRNA carrying the growing polypeptide chain.
On the large subunit of the ribosome. | |
| 489322158 | A site | One of the three binding sites for tRNA on the ribosome.
Holds the tRNA carrying the next amino acid to be added to the chain at the P site.
On the large subunit of the ribosome. | |
| 489322159 | E site | One of the three binding sites for tRNA on the ribosome.
Discharged tRNAs leave the ribosome from this site.
On the large subunit of the ribosome. | |
| 489322160 | Three Stages of Translation | (Analogous to transcription) Initiation, elongation, and termination. | |
| 489322161 | Initiation of Translation | First a small ribosomal subunit binds to both mRNA and a specific initiator tRNA, which carries the amino acid methionine.
The small subunit then moves downstream along the mRNA until it reaches the start codon AUG, which signals the start of translation and establishes the codon reading frame.
The initiator tRNA, already associated with the complex, then hydrogen bonds the start codon. This is followed by the attachment of a large ribosomal subunit, completing the translation initiation complex.
Initiation factors are required in order to bring all these components together--this requires energy in the form of GTP.
Once the initiation complex has formed, the initiator tRNA sits in the P site of the ribosome with the vacant A site ready for the next aminoacyl tRNA | |
| 489322162 | Initiation Factors | Required in order to bring all the components of the initiation complex together.
The initiation complex includes the small and large ribosomal subunits, the mRNA, the initiator tRNA (with amino acid methionine) and energy from GTP. | |
| 489322163 | Elongation Factors | Several proteins required for the elongation stage of translation.
In this stage, amino acids are added one by one to the preceding amino acid--each addition occurs in a 3 step cycle with energy expenditure in the first and last steps. | |
| 489322164 | Elongation Stage of Translation | Requires elongation factors.
Energy is expended in the first and third (last) steps.
Starts by codon recognition where the anticodon of an incoming tRNA base-pairs with the complementary mRNA codon in the A site, requiring the hydrolysis of 2 GTP to GDP.
Then, an rRNA molecule of the large subunit catalyzes the formation of a peptide bond between the new amino acid in the A site and the carboxyl end of the growing polypeptide in the P site, attaching the polypeptide to the tRNA in the A site.
The ribosome then translocates the tRNA in the A site to the P site while the empty tRNA in the P site moves to the E site where it is released. This process takes hydrolysis of 1 GTP. | |
| 489322165 | Termination of Translation | Elongation continues until a stop codon in the mRNA reaches the A site of the ribosome.
A protein called release factor binds directly to the stop codon in the A site, causing the addition of a water molecule instead of an amino acid to the chain. | |
| 489322166 | Release Factor | A protein that directly binds the stop codon in the A site during the termination phase of translation by causing the addition of a water molecule instead of an amino acid to the polypeptide chain. This hydrolyzes the completed polypeptide from the tRNA in the P site, releasing the polypeptide through the exit tunnel of the large subunit.
The translation assembly comes apart. | |
| 489322167 | Polyribosomes | Or polysomes.
Typically a single mRNA is used to make many copies of a polypeptide simultaneously because several ribosomes can translate the message from one mRNA at the same time.
Once a ribosome moves past the start codon, a second one can attach to the mRNA, ultimately making a trail along on mRNA molecule called the polyribosomes. | |
| 489322168 | Chaperone Protein | A protein that helps the polypeptide fold correctly.
During its synthesis, a chain begins to coil and fold spontaneously but sometimes requires this help. | |
| 489322169 | Post-translational Modifications | Steps that may be required before a protein can begin doing its particular job in a cell, directly after its translation.
Certain amino acids, for example, can be chemically modified by the attachment of sugars, lipids, phosphate groups, or other additions. Enzymes can also remove one or more amino acid from the leading end of the chain or can cleave a chain into two or move chains. In other cases, chains come together to become subunits of a protein with a quaternary structure. | |
| 489322170 | Signal Peptide | A peptide that marks proteins for the endomembrane system or for secretion, targeting the protein to the ER.
Seen at or near the leading end of the chain and is recognized by a protein-RNA complex called a signal-recognition particle (SRP).
Polypeptide synthesis always begins in the cytosol, when a free ribosome starts to translate the mRNA. It is not until the growing polypeptide itself cues the ribosome to attach to the ER through this signal peptide that the ribosome will become bound.
Polypeptide synthesis continues at the ER membrane and the growing polypeptide snakes across the membrane into the ER lumen via a protein pore. The polypeptide will either remain in the membrane or go into the lumen once translation is complete. | |
| 489322171 | Signal-recognition Particle (SRP) | Recognizes a signal peptide found at or near the leading end of a polypeptide chain. Recognition of this signal peptide targets the protein and ribosome translating it to the ER.
Brings the ribosome to a receptor protein built into the ER membrane. | |
| 489322172 | Small Nucelolar RNA (snoRNA) | A type of RNA that aids in processing pre-rRNA transcripts in the nucleolus, a process necessary for ribosome function. | |
| 489322173 | SRP RNA | A component of the signal-recognition particle (SRP), the protein-RNA complex that recognizes the signal peptides of polypeptides targeted to the ER. | |
| 489322174 | Type of RNA Involved in Regulation of Gene Expression | Small interfering RNA (siRNA) and microRNA (miRNA). | |
| 489322175 | 3 Important Properties that Allow RNA to Perform So Many Different Functions | 1. It can hydrogen-bond to other nucleic acids (RNA or DNA).
2. IT can assume a specific 3D shape by forming hydrogen bonds between bases in different parts of its own polynucleotide chain.
3. It has functional groups that allow it to act as a catalyst (ribozyme). | |
| 489322176 | Mutations | Changes in the genetic material of a cell.
Can be spontaneous or the result of mutagens. | |
| 489322177 | Point Mutations | Chemical changes in just one base pair of a gene.
If this occurs in a gamete or a cell that gives rise to a gamete, it may be transmitted to offspring an future generations. | |
| 489322178 | Types of Point Mutations | Base-pair substitutions, base-pair insertions, and base-pair deletions. | |
| 489322179 | Base-pair Substitutions | Type of point mutation.
The replacement of one nucleotide and its partner with another pair of nucleotides.
Some, but not all, cause a readily detectable change in a protein whether it be an improvement or it worsens the activity of the protein.
Usually missense mutations but can also be nonsense mutation. | |
| 489322180 | Silent Mutations | Some base-pair substitutions that occur owing to the redundancy of the genetic code.
They have no effect on the encoded protein. | |
| 489322181 | Missense Mutations | A substitution mutation in which the altered codon still codes for an amino acid and thus makes sense, although not necessarily the right sense. | |
| 489322182 | Nonsense Mutations | A substitution mutation in which the altered codon changes to a stop codon, causing translation to be terminated prematurely.
Causes the polypeptide to be shorter than the one that was supposed to be encoded.
Usually all lead to nonfunctional proteins. | |
| 489322183 | Base-pair Insertions | Type of point mutation.
Addition of nucleotide pairs in a gene.
Usually more disastrous than substitutions.
Usually results in frameshift mutation. | |
| 489322184 | Base-pair Deletions | Type of point mutation.
Loss of nucleotide pairs in a gene.
Usually more disastrous than substitutions.
Usually results in frameshift mutation. | |
| 489322185 | Frameshift Mutation | Often the result of base-pair insertions and deletions.
Occurs when the number of nucleotides inserted or deleted is not a multiple of 3, altering the reading frame of the genetic message. | |
| 489322186 | Spontaneous Mutations | Mutations that result during DNA replication, repair, or recombination which can lead to base-pair substitution, insertion or deletion as well as mutations affecting longer strands of DNA. | |
| 489322187 | Mutagens | Physical and chemical agents that interact with DNA in ways that cause mutations.
Most are carcinogens.
E.g. X-rays, other forms of high-energy radiation, and UV light. | |
| 489322188 | Carcinogens | Cancer-causing chemicals.
Usually mutagenic. | |
| 489322189 | Another Definition of a Gene | A gene is a region of DNA whose final product is either a polypeptide or an RNA molecule. | |
