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Questions and Answers
What is the main function of helicase during DNA replication?
What is the main function of helicase during DNA replication?
Which of the following correctly represents the pathway of gene expression?
Which of the following correctly represents the pathway of gene expression?
What distinguishes genotype from phenotype?
What distinguishes genotype from phenotype?
Which of the following components is NOT part of the basic structure of DNA?
Which of the following components is NOT part of the basic structure of DNA?
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Which statement about DNA replication is correct?
Which statement about DNA replication is correct?
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What role do single-strand binding proteins (SSB) play in DNA replication?
What role do single-strand binding proteins (SSB) play in DNA replication?
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Which type of RNA is synthesized during the transcription phase of gene expression?
Which type of RNA is synthesized during the transcription phase of gene expression?
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What component links the nucleotide subunits to form a new DNA strand during replication?
What component links the nucleotide subunits to form a new DNA strand during replication?
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What is the role of RNA polymerase in transcription?
What is the role of RNA polymerase in transcription?
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In the genetic code, what does the AUG codon signify?
In the genetic code, what does the AUG codon signify?
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What is the main purpose of transfer RNA (tRNA) during translation?
What is the main purpose of transfer RNA (tRNA) during translation?
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Which of the following components is NOT part of ribosomes?
Which of the following components is NOT part of ribosomes?
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Which process does not occur during transcription?
Which process does not occur during transcription?
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What signifies the end of the translation process?
What signifies the end of the translation process?
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During the elongation step of transcription, which direction does RNA polymerase synthesize the mRNA?
During the elongation step of transcription, which direction does RNA polymerase synthesize the mRNA?
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What is the significance of a polyribosome during protein synthesis?
What is the significance of a polyribosome during protein synthesis?
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Study Notes
Genetics
- Study of genes
- Genome holds all genetic information
- Genes are DNA fragments
- DNA is a double helix
- DNA is composed of nucleotides containing A, T, C, and G bases
- DNA contains a ribose (deoxyribose) group and phosphate group linked by hydrogen bonds
Chromatin
- Chromatin is the complex of DNA, RNA, and proteins found in the nucleus of eukaryotic cells
- It condenses during cell division to form chromosomes
Genotype & Phenotype
- Genotype: The sum of all genes that encode for the characteristics of an organism
- Phenotype: Refers to expressed properties and is the manifestation of the genotype
DNA Replication
- Each daughter double helix has an original strand from the parent and a newly synthesized complimentary strand
- Replication occurs when the two strands of the double helix unwind
- Each strand serves as a template for forming a new complementary strand
DNA Replication Enzymes
- Helicase: Opens the double helix by disrupting hydrogen bonds
- Single-strand binding protein: Prevents the helix from reforming before replication
- DNA polymerase: Links nucleotide subunits to form a new DNA strand from a DNA template
Nucleic Acids and Proteins
- Genes are converted into messenger RNA (mRNA)
- mRNA is transcribed into proteins
- Genes can also be converted to ribosomal RNA (rRNA) or transfer RNA (tRNA) which then produce proteins
Gene Expression
- Gene expression is the process by which DNA is expressed into proteins
- The two stages of gene expression are transcription and translation
Transcription
- Only one strand of DNA is translated into mRNA
- This strand is called the DNA template strand
- RNA bases include C, G, U, and A (U replaces T in DNA)
Translation
- The synthesized mRNA is read in a sequence of triplets
- Every three nucleotides form one amino acid
- Amino acids are joined together to form a protein
Codons
- The table includes 64 codons
- 61 codons encode amino acids
- Codons are read in the 5’→ 3’ direction
- The AUG codon codes for methionine, acting as the start codon for translation
- UAA, UAG, and UGA are stop codons, indicating the end of the translation process
Transcription Components
- RNA polymerase: The enzyme for transcription
- Transcription factors: Proteins needed for transcription
- Promoter and terminator: DNA sequences that control transcription
Transcription steps
- Initiation: Beginning of transcription
- Elongation: RNA polymerase moves down the DNA template strand, building mRNA
- Termination: Stop codons signal the end of transcription
Translation components
- Messenger RNA: Carries the genetic code
- Transfer RNA: Carries specific amino acids
- Ribosomes: Organelle responsible for protein synthesis
- Amino Acids: Building blocks of proteins
Transfer RNA (tRNA)
- tRNA pairs a complementary anticodon with a codon
- tRNA links the codon to a corresponding amino acid
- The anticodon is read in the 3’→ 5’ direction
Ribosomes
- Ribosomes consist of two subunits:
- A large subunit with three binding sites for tRNA
- A small subunit with a binding site for mRNA
Poly Ribosomes
- Poly Ribosomes allow multiple ribosomes to translate a single mRNA at a time
- This creates a functional protein
- Microscopic observation shows polyribosomes
Eukaryotic Cell
- In eukaryotic cells, translation and transcription occur at different locations
- Transcription takes place in the nucleus
- Translation takes place in the cytoplasm
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