Untitled Flashcards Set

Central Dogma

• The first step of DNA expression is to turn it into RNA. The RNA is then sent out into the cell and often gets turned into a protein.

• These proteins, in turn, regulate almost everything that occurs in the cell.

• The process of making an RNA from DNA is called transcription, and the process of making a protein from an RNA is called translation.

DNA - mRNA via transcription - protein via translation

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RNA

1.RNA is single-stranded.

2. The 5-carbon sugar in RNA is ribose instead of deoxyribose.

3. Uracil replaces thymine as adenine’s partner.

• Messenger RNA (mRNA) is a temporary RNA version of a DNA recipe that gets sent to the ribosome.

• Ribosomal RNA (rRNA), makes up part of the ribosomes.

• Transfer RNA (tRNA) brings amino acids to the ribosomes. It brings the brings a specific amino acid into place at the appropriate time by matching anticodons to codons. It does by reading the message carried by the mRNA.

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Transcription

• Transcription involves making an RNA copy of a bit of DNA code.

• In replication we end up with a complete copy of the cell’s DNA, in transcription we end up with only a tiny specific section copied into an mRNA.

• Transcription begins at special sequences of the DNA strand called promoters.

• The official starting point is called the start site.

• We copy only one of the two DNA strands.

• The strand that serves as the template is known as the antisense strand.

• The other strand that lies dormant is the sense strand, or the coding strand.

• RNA polymerase builds RNA by adding nucleotides only to the 3′ side, therefore building a new molecule from 5′ to 3′

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RNA Processing

• The regions that express the code are exons.

• The noncoding regions in the mRNA are introns.

• Prokaryotes will transcribe a recipe that can be used to make several proteins. This is called a polycistronic transcript.

• Eukaryotes tend to have one gene that gets transcribed to one mRNA and translated into one protein. Our transcripts are monocistronic.

• The introns must be removed before the mRNA leaves the nucleus. This process, called splicing, is accomplished by an RNA-protein complex called a spliceosome.

• In addition, a poly(A) tail is added to the 3′ end

• And, a 5′ GTP cap is added to the 5′ end.

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Translation

• mRNA —> protein

• Process occurs on ribosomes in cytoplasm and on the rough endoplasmic reticulum

• 3 nucleotides is called a codon. Each codon corresponds to a particular amino acid.

• One end of the tRNA carries an amino acid. The other end, called an anticodon, has three nitrogenous bases that can complementarily base pair with the codon in the mRNA.

• The third position is said to experience wobble pairing. Things that don’t normally bind will pair up, like guanine and uracil.

• Translation also involves three phases: initiation, elongation, and termination.

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Initiation

• It begins when a ribosome attaches to the mRNA.

• Ribosomes contain three binding sites: an A site, a P site, and an E site. The mRNA will shuffle through from A to P to E. As the mRNA codons are read, the polypeptide will be built.

• The start codon is A–U–G, which codes for the amino acid methionine.

• The tRNA with the complementary anticodon, U– A–C, is methionine’s personal shuttle; when the AUG is read on the mRNA, methionine is delivered to the ribosome.

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Elongation

• Addition of amino acids is called elongation and when many amino acids link up, a polypeptide is formed.

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Termination

The synthesis of a polypeptide is ended by stop codons. There are three that serve as a stop codon. Termination occurs when the ribosome runs into one of these three stop codons.

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Regulation of Zene Expression and Cell Specialization

• Regulation of gene expression can occur at different times. The largest point is before transcription, or pre-transcriptional regulation.

• Transcription factors can encourage or inhibit this from happening.

• Sometimes changes to the packaging of DNA will alter the ability of the transcription machinery to access a gene, this is called epigenetic changes.

• In bacteria, a cluster of genes can be under the control of a single promoter; these functioning units of DNA are called operons.

• The operon consists of four major parts:

structural genes, promoter genes, the operator, and the regulatory gene:

• Structural genes code for enzymes needed in a chemical reaction. These genes will be transcribed at the same time to produce particular enzymes.

• The promoter gene is the region where the RNA polymerase binds to begin transcription.

• The operator is a region that controls whether transcription will occur; this is where the repressor binds.

• The regulatory gene codes for a specific regulatory protein called the repressor. The repressor is capable of attaching to the operator and blocking transcription.

• Post-transcriptional regulation occurs when the cell creates an RNA, but then decides that it should not be translated into a protein. This is where RNAi comes into play.

• RNAi molecules can bind to an RNA via complementary base pairing. This creates a double-stranded RNA

• Post-translational regulation can also occur if a cell has already made a protein, but doesn’t yet need to use it.

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Gene Regulation in Embryonic Development

• The cell changes shape and organization many times by going through a succession of stages. This process is called morphogenesis.

• Fertilization triggers the zygote to go through a series of cell divisions.

• The early genes that turn certain cells in the early embryo into future-this or future-that are called homeotic genes. A subset of homeotic genes are called Hox genes.

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Mutations

• A mutation is an error in the genetic code.

• Mutations can occur because DNA is damaged caused by chemicals or radiation and cannot be repaired or because DNA damage is repaired incorrectly.

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Base Substitution

• Base substitution (point) mutations result when a single nucleotide base is substituted for another. There are three different types of point mutations:

• Nonsense mutations cause the original codon to become a stop codon, which results in early termination of protein synthesis.

• Missense mutations cause the original codon to be altered and produce a different amino acid.

• Silent mutations happen when a codon that codes for the same amino acid is created and therefore does not change the corresponding protein sequence.

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Gene Rearrangements

1. Insertions and deletions result in the gain or loss, respectively, of DNA or a gene. Introduction or deletion of bases often results in a change in the sequence of codons used by the ribosome (called a frameshift mutation) to synthesize a polyprotein.

2. Duplications can result in an extra copy of genes and are usually caused by unequal crossing-over during meiosis or chromosome rearrangements. This may cause a new trait

3. Inversions can result when changes occur in the orientation of chromosomal regions

4. Translocations occur when two different chromosomes break and rejoin in a way that causes the DNA sequence or gene to be lost, repeated, or interrupted.

5. Transposons are gene segments that can cut/paste themselves throughout the genome. Its presence can interrupt a gene and cause errors in gene expression.

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• Bacteria are prokaryotes that come in many shapes and sizes.

• Bacteria divide by fission; however, this does not increase their genetic diversity. Instead, they can perform conjugation with other bacterial cells and swap some of their DNA.

• Viruses are nonliving agents capable of infecting cells since they require a host cell’s machinery in order to replicate.

• A virus has two main components:

  • a protein shell (the capsid)

  • genetic material made of DNA or RNA.

  The thing infected by a virus is called a host.

• Bacteriophages undergo two different types of replication cycles, the lytic cycle and the lysogenic cycle.

• In the lytic cycle, the virus immediately starts using the host cell’s machinery to replicate the genetic material and create more capsid proteins.

• The transfer of DNA between bacterial cells using a lysogenic virus is called transduction.

• Viruses with a lipid envelope are called enveloped viruses.

• Retroviruses like HIV are RNA viruses that use an enzyme called reverse transcriptase to convert their RNA genomes into DNA so that they can be inserted into a host genome.

Biotechnology

• Recombinant DNA is generated by combining DNA from multiple sources to create a unique DNA molecule that is not found in nature.

• A common application of recombinant DNA technology is the introduction of a eukaryotic gene of interest into a bacterium for production for research and to cure diseases

• This technology that produces new organisms or products by transferring genes between cells is called genetic engineering.

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Polymerase Chain Reaction (PCR)

• PCR is a laboratory technique that is used to create billions of identical copies of genes within hours.

• The process of creating many copies of genes is known as amplification.

• The process of giving bacteria foreign DNA is called transformation.

• A technique that is alike, is transfection, which is putting a plasmid into a eukaryotic cell, rather than a bacteria cell.

• DNA fragments can be separated according to their molecular weight and charge with gel electrophoresis. Since DNA and RNA are negatively charged, they go through a gel toward the positive pole of the electrical field.

• When restriction fragments between individuals of the same species are compared, the fragments differ in length because of polymorphisms, which are differences in DNA sequences.

• These fragments are called restriction fragment length polymorphisms, or RFLPs.

• DNA sequencing allows scientists to determine the order of nucleotides in a DNA molecule. Scientists could design their own DNA plasmid and use it to study a gene of interest.

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