DNA is made up of repeated subunits of nucleotides. Each nucleotide has a five-carbon sugar, a phosphate, and a nitrogenous base.
The name of the pentagon-shaped sugar in DNA is deoxyribose. Hence, the name deoxyribonucleic acid. Notice that the sugar is linked to two things: a phosphate and a nitrogenous base. A nucleotide can have one of four different nitrogenous bases:
Prokaryotes and eukaryotes can also contain plasmids, which are small double-stranded, circular DNA molecules. The nucleotides can link up in a long chain to form a single strand of DNA
The nucleotides themselves are linked together by phosphate bonds between the sugars and the phosphates. This is called the sugar-phosphate backbone of DNA and it serves as a scaffold for the bases.
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The ones you’ll need to know for the AP Biology Exam are DNA helicase, DNA polymerase, DNA ligase, topoisomerase, and RNA primase:
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DNA - mRNA via transcription - protein via translation
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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 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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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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Addition of amino acids is called elongation and when many amino acids link up, a polypeptide is formed.
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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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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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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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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:
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.
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