Biology - Chapters 7-8 Genes and Protein Synthesis & Genetic Technologies Review

What did Beadle and Tatum’s experiments in the 1940s show?

(Genes and protein synthesis note)

a direct relationship between genes and enzymes

What is a minimal medium?

(Genes and protein synthesis note)

a medium that contains only several salts, sucrose, and a vitamin, and does not contain any of the other more complex chemicals required by cells

Describe Beadle and Tatum’s experiments

(Genes and protein synthesis note)

• grew an orange coloured bread mould (Neurospora crassa) in a minimal medium

• Neurospora crassa readily grew

  • means that the mould could use the simple chemicals in the MM to synthesize the more complex compounds it required for growth and reproduction

  • enzymes are necessary for all of these metabolic reactions

• spores of the N. crassa were exposed to X-Rays, causing random mutations in genes

• it was reasoned that some of the altered genes were responsible for essential metabolic activities

  • correct because some of the mutated spores no longer grew on the MM

What hypothesis did Beadle and Tatum put forward?

(Genes and protein synthesis note)

the one gene - one enzyme hypothesis

Explain the one gene - one enzyme hypothesis

(Genes and protein synthesis note)

each gene is unique and codes for the synthesis for a single protein

What was the one gene - one enzyme hypothesis restated as?

(Genes and protein synthesis note)

the one gene - one polypeptide hypothesis

Explain the one gene - one polypeptide hypothesis

(Genes and protein synthesis note)

each gene is unique and codes for the synthesis of a single polypeptide

Genes are essential for ______ _________

(Genes and protein synthesis note)

protein synthesis

Who named the central dogma?

(Genes and protein synthesis note)

Francis Crick in 1965

What is the central dogma?

(Genes and protein synthesis note)

the flow of information from DNA →RNA → Protein

What is transcription?

(Genes and protein synthesis note)

a mechanism by which the information coded in nucleic acids of DNA is transcribed into a complementary copy

the information in one type of nucleic acid (DNA) is copied onto another type of nucleic acid (RNA)

Where does transcription occur?

(Genes and protein synthesis note)

in the nucleus of cells as DNA cannot leave the nucleus

What is translation?

(Genes and protein synthesis note)

the information encoded in the RNA is used to assemble amino acids into polypeptides

Where does translation occur?

(Genes and protein synthesis note)

it takes place in the ribosomes in the cytoplasms

Differences between RNA to DNA

(Genes and protein synthesis note)

• DNA

  • double stranded

  • A pairs with T

  • deoxyribose sugar

• RNA

  • single stranded

  • A pairs with U

  • ribose sugar

What are the 3 major types of RNA?

(Genes and protein synthesis note)

mRNA, tRNA, and rRNA

give the characteristics and key functions of mRNA

(Genes and protein synthesis note)

• no set length (varies)

• acts as an intermediary between the DNA and the ribosomes

• is translated into protein by the ribosomes

• is the RNA version of the gene encoded by DNA

give the characteristics and key functions of tRNA

(Genes and protein synthesis note)

• transfers the appropriate amino acid to the ribosome to build a protein

• is very short (70-90 base pairs long)

give the characteristics and key functions of rRNA

(Genes and protein synthesis note)

• is a structural component of a ribosome

• no set length (varies)

the specific amino acid coded for by a particular DNA (or complementary RNA) base is determined by…

(Genes and protein synthesis note)

the bases (A, T, C, and G)

What is a codon?

(Genes and protein synthesis note)

a 3 base letter code

What order are codons in?

(Genes and protein synthesis note)

the 5’ to 3’ order in the mRNA and subsequently in the amino acid sequence of a polypeptide

What is a ‘sense codon’?

(Genes and protein synthesis note)

a codon that codes for amino acids

What is the ‘start’ codon?

(Genes and protein synthesis note)

AUG, which codes for MET (methionine)

What are ‘nonsense’ codons?

(Genes and protein synthesis note)

• codons that do not code for any amino acid

• also known as stop codons

• VAA, VAG, and VGA

What is the wobble hypothesis/redundancy?

(Genes and protein synthesis note)

the 3rd base in a codon changes/wobbles while still producing the same amino acid

The genetic code is __________

(Genes and protein synthesis note)

universal

• the same codons specify for almost all living organisms, suggesting that it was established very early on during evolution

What are the 3 stages of transcription?

(transcription note)

1. initiation

2. elongation

3. termination and post-transcriptional modifications

Explain the first stage of transcription

(transcription note)

initiation:

• Promoter Binding: RNA polymerase binds to the promoter region of the gene, with the help of transcription factors in eukaryotes.

• DNA Unwinding: RNA polymerase unwinds a short stretch of the DNA double helix to expose the template strand.

• RNA polymerase knows where to attach when it recognizes a promoter

What is a promoter?

(transcription note)

a specialized sequence on one of the DNA strands located just upstream from the beginning of the gene.

what is a promoter known as in Eukaryotes?

(transcription note)

the TATA box

What is the TATA box in Eurkaryotes?

(transcription note)

a section of DNA with a high percentage of thymine and adenine bases

Explain the second stage of transcription

(transcription note)

Elongation:

• the RNA polymerase begins to build the single stranded RNA molecule

• RNA is made in the 5’ to 3’ direction using the 3’ to 5’ direction

• the growing RNA molecule elongates and eventually extends from the RNA polymerase as a single nucleotide chain. As the RNA polymerase passes, the DNA double helix reforms

What is the coding strand?

(transcription note)

The opposite DNA strand that is not being copied

Explain the third stage of transcription

(transcription note)

Termination

• RNA polymerase continues until it reaches the terminator sequence.

• The RNA strand is released, and RNA polymerase detaches from the DNA.

Explain post-transcriptional modifications (Eukaryotes only)

(transcription note)

• 5' Capping: A 5’ cap, consisting of 7 Guanine bases, is added. Ribosomes recognize this site and use it as the site of initial attachment

• Polyadenylation: A poly-A tail (a long chain of adenine nucleotides) to the 3' end to protect the mRNA from degradation due to enzymes in the cytosol

• Splicing: Removal of introns (non-coding regions) and joining of exons (coding regions) by the spliceosome.

Exons:

(transcription note)

sequences of RNA or DNA that codes for part of a gene

Introns:

(transcription note)

non-coding sequences of DNA or RNA

__________ includes both exons and introns

(transcription note)

pre-mRNA

Why can’t introns be left in?

(transcription note)

They would alter the sequence of the protein that needs to be made

What are introns removed by?

(transcription note)

an enzyme-protein complex called spliceosome

Where does transcription occur in prokaryotes?

(transcription note)

Throughout the cell

Where does transcription occur in Eukaryotes?

(transcription note)

in the nucleus

What types of enzymes are present in prokaryotes?

(transcription note)

a single type of RNA polymerase transcribes all types of genes

What types of enzymes are in eukaryotes?

(transcription note)

different RNA polymerases are used to transcribe genes that encode protein (RNA polymerase II) and genes that do not encode protein (RNA polymerase I)

How are bases added in prokaryotes?

(transcription note)

bases are added quickly (15-20 nucleotides per second)

how are bases added in eukaryotes?

(transcription note)

bases are added slowly (5-8 nucleotides per second)

complexity of promoters in prokaryotes

(transcription note)

less complex than eukaryotes

complexity and location of promoters in eukaryotes

(transcription note)

located immediately upstream of protein-coding genes, and they are more complex than prokaryotes

describe termination in prokaryotes

(transcription note)

a protein binds to the mRNA and cleaves it, or the mRNA binds with itself

describe termination in eukaryotes

(transcription note)

nuclear proteins bind to the polyuracil site and terminate transcription

introns and exons in prokaryotes

(transcription note)

no introns, only exons

introns and exons in eukaryotes

(transcription note)

both introns and exons

product in prokaryotes

(transcription note)

transcription results in mRNA ready to be translated into proteins by ribosomes

product in eukaryotes

(transcription note)

transcription results in pre-mRNA, which must be modified to protect the final mRNA from degradation in the cytosol and to remove the introns

the information encoded in the ____ is used to assemble ______ ____ into __________. this takes place in the _______ in the ________

(translation note)

mRNA, amino acids, polypeptides, ribosomes, cytoplasm

tRNA:

(translation note)

transfer RNA is a carrier molecule that binds to a specific amino acid and adds that amino acid to the growing polypeptide chain

where do each tRNA molecule carry an amino acid?

(translation note)

at one end. at the other end there is a specific anticodon

what are ribosomes made up of?

(translation note)

made up of 2 different sized parts: a large subunit an a small subunit, both made up of ribosomal RNA and ribosomal proteins

the mRNA threads between the subunits of the ________

(translation note)

ribosomes

incoming _____ molecules join up to the mRNA codon by matching their anticodon

(translation note)

tRNA

3 major stages

(translation note)

1. initiation

2. elongation

3. termination

how is the production of crucial proteins increased?

(translation note)

multiple ribosomes can translate the same mRNA molecule at the same time

this happens in both Eurkaryotes and Prokaryotes

what happens when multiple ribosomes translate the same mRNA molecule at the same time?

(translation note)

it results in a complex called polysome

where is mRNA translated in prokaryotes?

(translation note)

in the cytosol

where is mRNA transcribed in eukaryotes?

(translation note)

• mRNA can only be translated after exiting the nucleus to interact the ribosomes in the cytosl

• some translation occurs in the mitochondria and chloroplasts

describe initiation in prokaryotes:

(translation note)

• mRNA bases pair directly with a ribosomal binding site, just upstream of the start codon

• mRNA 5’ cap is involved

describe initiation in eukaryotes:

(translation note)

complex of Met-tRNA, with small ribosomal subunits, binds to an mRNA 5’ cap and scans it until it encounters the start codon

how many elongation cycles per second in prokaryotes?

(translation note)

15-20 elongation cycles per second

how many elongation cycles per second in eukaryotes?

(translation note)

1-3 elongation cycles per second

describe termination in prokaryotes and eukaryotes:

(translation note)

stop codon appears and a release factor binds so that the polypeptide is released

can mRNA strands in prokaryotes be translated by multiple ribosomes simultaneously?

(translation note)

yes, even as it is being transcribed from DNA

can mRNA strands in prokaryotes be translated by multiple ribosomes simultaneously?

(translation note)

mRNA strands can be translated by multiple ribosomes simultaneously, but only in the cytosol

what is a genetic mutation?

(Textbook Worksheet - Genetic Mutation)

changes in the DNA sequence, caused by various mechanisms

What is a point mutation?

(Textbook Worksheet - Genetic Mutation)

a change in a single nucleotide within a gene

What increases a smoker’s risk of developing lung cancer?

(Textbook Worksheet - Genetic Mutation)

Mutation in a region on chromosome 15 can increase lung cancer risk by 30-80% in smokers, depending on the number of copies of the 15q24 susceptibility locus.

Substitution:

(Textbook Worksheet - Genetic Mutation)

the replacement of one base pair in a DNA sequence by another base pair

Insertion:

(Textbook Worksheet - Genetic Mutation)

the addition of a base pair (small-scale mutation) or larger coding region (large-scale muttion) to a DNA sequence

Deletion:

(Textbook Worksheet - Genetic Mutation)

the removal of a base pair (small-scale mutation)or larger coding region (large-scale mutation) to a DNA sequence

Inversion:

(Textbook Worksheet - Genetic Mutation)

two adjacent bases trading places (small-scale mutation) or the reversal of a sequence of DNA (large-scale mutation)

What are SNP’s?

(Textbook Worksheet - Genetic Mutation)

a difference in the DNA between individuals caused by point mutatons

When does a missense mutation occur?

(Textbook Worksheet - Genetic Mutation)

occurs when a change of a single base pair or group of base pairs results in the code for a different amino acid

What happens to the protein structure that is synthesized when a missense mutation occurs?

(Textbook Worksheet - Genetic Mutation)

it will have a different sequence or structure, and it may be non-functional or function differently

When does a nonsense mutation occur?

(Textbook Worksheet - Genetic Mutation)

occurs when the change of a single base pair or group of base pairs results in a premature stop code in the gene

What happens to the polypeptide in a nonsense mutation?

(Textbook Worksheet - Genetic Mutation)

it is cut shot, and will most likely be unable to function

When does a silent mutation occur?

(Textbook Worksheet - Genetic Mutation)

occurs when the change in one or more base pairs does not affect the functioning of the gene

What is the effect of a silent mutation on the resulting protein?

The resulting protein is not altered, as the mutated DNA sequence codes for the same amino acid as the non-mutated sequence

When does a frameshift mutation occur?

(Textbook Worksheet - Genetic Mutation)

occurs when one or more nucleotides are inserted into or deleted from a DNA sequence, causing the reading frame of codons to shift in one direction or the other

What do frameshift mutations result in?

(Textbook Worksheet - Genetic Mutation)

they result in multiple missense and/or nonsense mutations

Describe how a framework mutation occurs

it “shifts” the reading frame by one or more steps, and every amino acid coded for after this mutation is affected

When is a frameshift mutation not caused?

(Textbook Worksheet - Genetic Mutation)

any deletion or insertion of base pairs in multiples of 3 do not cause any frameshifts because the reading frame is unaltered

What is Tay-Sachs disease a result of?

(Textbook Worksheet - Genetic Mutation)

It is a result of the insertion of 4 base pairs

What are large-scale mutations?

(Textbook Worksheet - Genetic Mutation)

mutations that involve multiple nucleotides, entire genes, or whole regions of chromosomes

What is chromosomal translocation?

(Textbook Worksheet - Genetic Mutation)

the movement of entire genes or sequences of DNA from one chromosome to another

Differences between spontaneous mutations and induced mutations

• spontaneous mutations:

  • a mutation that is caused by an error in DNA replication

• induced mutations:

  • a mutation that is caused by an environmental agent

What is a mutagen?

(Textbook Worksheet - Genetic Mutation)

an environmental agent that directly alters the DNA within a cell (eg. chemicals and radiation)

What is a genome?

Genomes, Gene Organization, and Viruses

a complete set of an organism’s hereditary information

What does the genome of eukaryotes contain?

Genomes, Gene Organization, and Viruses

• coding regions

• non-coding regions made up of introns (within genes)

• repeating sequences (between genes)

What are the different types of repeating sequences?

Genomes, Gene Organization, and Viruses

• VNTRs (variable number tandem repeats)

• LINEs (long interspersed nuclear elements)

• SINEs (short interspersed nuclear elements)

What are VNTRs?

Genomes, Gene Organization, and Viruses

repeating sequences of base pairs of varying lengths (eg. TAGTAGTAGTAG)