intro to genetics

A collection of flashcards summarizing key concepts from the lecture on DNA, RNA, PCR, and translation processes.

What is the function of the primers in PCR reactions?

Primers provide a starting point for DNA synthesis during PCR by annealing to the template DNA strands and allowing DNA polymerase to begin synthesizing a new strand.

What is gel electrophoresis used for?

Gel electrophoresis is used to separate DNA fragments based on their size and charge, typically by applying an electric current that moves the fragments through a gel matrix.

What is the difference between homologous ALU fragments in the PV92 region and no ALU repeats?

Homologous ALU fragments in the PV92 region indicate the presence of the ALU gene on both chromosomes (homozygous for the insertion), whereas no ALU repeats show its absence (homozygous for the absence), or heterozygous condition if one chromosome has it and the other doesn't.

What are the different forms of RNA?

The primary forms of RNA are:

• mRNA (messenger RNA): Carries genetic information from DNA to ribosomes for protein synthesis.
• tRNA (transfer RNA): Transports specific amino acids to the ribosome during translation, matching them to codons on mRNA.
• rRNA (ribosomal RNA): A structural and catalytic component of ribosomes, essential for protein synthesis.

How do you calculate the amounts of nitrogenous bases in DNA?

The amounts of nitrogenous bases in DNA are calculated by applying Chargaff's rules, which state that in double-stranded DNA, the concentration of adenine (A) is approximately equal to thymine (T), and the concentration of cytosine (C) is approximately equal to guanine (G). Thus, (A=T) and (C=G).

What is the role of topoisomerase in DNA replication?

Topoisomerase is an enzyme that relieves the torsional strain and supercoiling ahead of the replication fork, which is caused by the unwinding of the DNA double helix during replication. It does this by cutting, unwinding, and rejoining DNA strands.

What are SSB proteins and what do they do?

SSB proteins are Single-Strand Binding proteins. They bind to and stabilize the separated single DNA strands after helicase unwinds the double helix, preventing them from re-annealing or being degraded during DNA replication.

What is the leading strand in DNA replication?

The leading strand in DNA replication is the new DNA strand that is synthesized continuously in the 5' to 3' direction, moving towards the replication fork with only one primer.

What is the lagging strand in DNA replication?

The lagging strand in DNA replication is the new DNA strand that is synthesized discontinuously, in the direction away from the replication fork. It forms short segments called Okazaki fragments, each requiring a new primer.

What type of bonds are present in DNA?

DNA contains two main types of bonds:

• Covalent bonds: Form the strong sugar-phosphate backbone of each strand.
• Hydrogen bonds: Weaker bonds that form between complementary nitrogenous bases (A with T, C with G) joining the two strands of the double helix.

What are the different parts of a DNA molecule?

A DNA molecule is a double helix composed of repeating monomer units called nucleotides. Each nucleotide consists of three parts:

• A five-carbon deoxyribose sugar.
• A phosphate group.
• One of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T).

What are the steps of DNA replication?

The main steps of DNA replication are:

1. Initiation: Unwinding of the DNA double helix at the origin of replication.
2. Elongation: Synthesis of new DNA strands by DNA polymerases, guided by the template strands.
3. Termination: Completion of DNA synthesis and release of the two new DNA molecules.

What are Okazaki fragments?

Okazaki fragments are short DNA segments (100-200 nucleotides in eukaryotes, 1000-2000 in prokaryotes) synthesized discontinuously on the lagging strand during DNA replication. These fragments are later joined together by DNA ligase to form a continuous strand.

What are the roles of different DNA polymerases?

DNA polymerases are enzymes that synthesize new DNA strands by adding nucleotides, complementary to a template strand, primarily during DNA replication and repair. In prokaryotes, DNA Pol III is the main replicative enzyme, while DNA Pol I replaces RNA primers with DNA. Eukaryotes have multiple DNA polymerases with specialized roles during replication and repair.

Where does transcription take place?

In eukaryotic cells, transcription primarily takes place in the nucleus, where the DNA template is located. In prokaryotic cells, transcription occurs in the cytoplasm.

Where is the promoter located in a gene?

The promoter is a DNA sequence located upstream (towards the 5' end) of the coding region of a gene. It acts as a binding site for RNA polymerase and transcription factors, indicating where transcription should begin.

What is the TATA box?

The TATA box is a conserved promoter sequence (typically 5' -TATAAT- 3' or 5' -TATAAA- 3') found in the promoter regions of many eukaryotic genes, usually located approx. 25-35 base pairs upstream of the transcription start site. It serves as a key recognition site for general transcription factors, facilitating the binding of RNA polymerase II to initiate transcription.

What is a 3' polyA tail?

A polyA tail is a stretch of about 50-250 adenine nucleotides that is added post-transcriptionally to the 3' end of most eukaryotic messenger RNA (mRNA) molecules. Its main functions include protecting the mRNA from enzymatic degradation, aiding in the export of mRNA from the nucleus, and promoting the initiation of translation.

How do you transcribe a strand of DNA to mRNA?

To transcribe a strand of DNA to mRNA, RNA polymerase reads the template DNA strand in the 3' to 5' direction and synthesizes a complementary RNA strand in the 5' to 3' direction. During this process, adenine (A) in DNA pairs with uracil (U) in RNA, thymine (T) in DNA pairs with adenine (A) in RNA, guanine (G) pairs with cytosine (C), and cytosine (C) pairs with guanine (G).

How many codons code for amino acids?

Out of the 64 possible codons in the genetic code, 61 codons specify one of the 20 standard amino acids. The remaining three codons (UAA, UAG, UGA) are stop codons, which signal the termination of translation and do not code for any amino acid.

What are the steps of transcription?

The main steps of transcription are:

1. Initiation: RNA polymerase binds to the promoter sequence, DNA unwinds, and RNA synthesis begins.
2. Elongation: RNA polymerase moves along the DNA template, synthesizing a complementary RNA strand.
3. Termination: RNA polymerase reaches a terminator sequence, causing the release of the RNA transcript and detachment of the polymerase from DNA.

What is degeneracy in the genetic code?

Degeneracy (or redundancy) in the genetic code refers to the fact that most amino acids are specified by more than one codon. For example, six different codons encode for the amino acid leucine. This redundancy provides some protection against the effects of point mutations.

What is the difference between a codon and an anti-codon?

A codon is a three-nucleotide sequence on an mRNA molecule that specifies a particular amino acid or a stop signal during protein synthesis. An anti-codon is a complementary three-nucleotide sequence located on a tRNA molecule that base-pairs with a specific codon on the mRNA during translation, ensuring the correct amino acid is delivered to the ribosome.

What are the jobs of the A site, E site, and P site during translation?

During translation, within a ribosome:

• A site (Aminoacyl-tRNA site): Holds the incoming aminoacyl-tRNA, which carries the next amino acid to be added to the polypeptide chain.
• P site (Peptidyl-tRNA site): Holds the tRNA attached to the growing polypeptide chain.
• E site (Exit site): Is where deacylated tRNAs (tRNAs that have delivered their amino acid) exit the ribosome.

How do you translate a strand of mRNA to a polypeptide?

Translating a strand of mRNA to a polypeptide involves ribosomes reading the mRNA codons (three-nucleotide sequences). Starting from the start codon (usually AUG), transfer RNA (tRNA) molecules, each carrying a specific amino acid and a complementary anti-codon, bind to the mRNA codons. The ribosome catalyzes the formation of peptide bonds between the amino