DNA & Proteins: Foundations and Discoveries

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Questions and Answers

What was the primary goal of Frederick Griffith's experiments in 1928?

To discover the genetic patterns in plants

To find a vaccine for Streptococcus pneumoniae (correct)

To prove the existence of DNA

To identify the specific structure of R cells

Which strain of bacteria was found to be pathogenic in Griffith's experiments?

Live S strain (correct)

Dead R strain

Heat-killed S strain

Live R strain

What was the outcome of the fourth experiment where live R cells were mixed with heat-killed S cells?

The mice developed pneumonia and died (correct)

The mice survived without any symptoms

No S cells were found in their blood

The R cells transformed into S cells

Why did Griffith conclude that R cells did not mutate during the experiments?

The first experiment resulted in healthy mice Signup and view all the answers

Which scientist is known for studying the patterns of genetics with plant phenotypes prior to Griffith's work?

Gregor Mendel Signup and view all the answers

What type of bond connects the nucleotides in the DNA backbone?

Phosphodiester bonds Signup and view all the answers

Which base pairs specifically bind together in DNA?

Adenine and Thymine Signup and view all the answers

Which of the following correctly identifies a difference between RNA and DNA?

DNA has deoxyribose, while RNA has ribose Signup and view all the answers

What effect does the incorrect pairing of two purines have on the structure of DNA?

It creates a bulge in the double helix Signup and view all the answers

What role does RNA serve in protein formation?

It acts as the foreman and construction workers Signup and view all the answers

What process involves the migration of genes from the S strain to the R strain?

Bacterial conjugation Signup and view all the answers

Which method did Rosalind Franklin utilize to study DNA structure?

X-ray crystallography Signup and view all the answers

What was a significant finding from experiments involving dead cells of infectious strains?

They indicated DNA can transform inert strains. Signup and view all the answers

What happens to cells when enzymes that digest DNA are added?

Cells stop functioning. Signup and view all the answers

Which of the following components are nucleotides in DNA made of?

Adenine, Thymine, Guanine, Cytosine Signup and view all the answers

Which statement about nucleic acids in viruses is true?

The majority of the virus remains outside the cell during infection. Signup and view all the answers

Why was Rosalind Franklin not awarded a Nobel Prize?

Nobel prizes are not awarded posthumously. Signup and view all the answers

What is the term for a sequence of three nucleotides that encodes one amino acid?

Codon Signup and view all the answers

What is the outcome of a frameshift mutation?

A change in the entire DNA sequence Signup and view all the answers

Which of the following is NOT considered a common mutagen?

Oxygen Signup and view all the answers

What significant observation was made regarding biodiversity in surface oceans?

60-70 million new species were discovered Signup and view all the answers

How do mutations contribute to evolution?

By leading to variation which allows for population changes Signup and view all the answers

What was the result of the single point mutation in the fruit fly?

The fly developed a leg in place of an antenna Signup and view all the answers

What can result from the replication of genes within the genome?

Multiple copies of the same gene Signup and view all the answers

What role do mutations play in organism adaptation?

They create new metabolic processes Signup and view all the answers

Why do birds lack teeth?

Teeth weigh too much for effective flight Signup and view all the answers

What role does the tRNA play in protein synthesis?

It has an anticodon that corresponds to the mRNA codon. Signup and view all the answers

Which of the following describes the function of ribosomes during translation?

They ensure that the amino acids are connected in the right order. Signup and view all the answers

What happens during the initiation stage of translation?

A tRNA carrying the start anticodon binds with the mRNA. Signup and view all the answers

Which process concludes when a stop codon is encountered during translation?

Termination occurs with the release of the protein. Signup and view all the answers

What is a silent mutation in the context of protein formation?

A mutation that does not affect protein synthesis. Signup and view all the answers

What type of mutation occurs when one or more base pairs are added to the DNA sequence?

Base insertion mutation. Signup and view all the answers

How do ribosomes facilitate the binding of mRNA and tRNA molecules?

They provide an active site that mimics enzyme activity. Signup and view all the answers

What can result from point mutations in the genetic code?

They can create variations in protein structure. Signup and view all the answers

What is the main role of RNA Polymerase II?

To synthesize messenger RNA Signup and view all the answers

What is a key difference between DNA and RNA in the context of nucleotides?

RNA contains Uracil, while DNA contains Thymine Signup and view all the answers

Which of the following statements about exons and introns is correct?

Exons code for proteins while introns do not. Signup and view all the answers

What is the function of mRNA in the cell?

To carry gene information from DNA for protein synthesis Signup and view all the answers

Where does transcription start in the DNA structure?

At the promoter region Signup and view all the answers

Which of the following is true about ribosomal RNA (rRNA)?

It constitutes a significant portion of ribosome mass. Signup and view all the answers

During translation, which type of RNA carries specific amino acids?

tRNA Signup and view all the answers

What role does the 5' cap serve in the final structure of mRNA?

Binds mRNA to ribosomes Signup and view all the answers

What is the function of stop codons in translation?

They indicate the end of the protein synthesis. Signup and view all the answers

What occurs during the process of translation?

Proteins are formed based on mRNA sequence. Signup and view all the answers

Study Notes

DNA & Proteins

DNA and proteins are fundamental to life.
Early theories proposed a hereditary agent, but concrete macromolecules weren't identified.
Darwin studied heredity, but lacked the mathematical tools to interpret his findings.
Mendel's experiments on plant phenotypes exposed patterns of heredity.

Discovery of DNA's Purpose

Frederick Griffith (1928) experimented with bacteria (streptococcus pneumoniae).
He experimented with two types of bacterial cells:
- S strain bacteria (smooth): pathogenic
- R strain bacteria (rough): non-pathogenic
A key finding was when heating-killed S strain bacteria and mixing it with live R bacteria, the R bacteria transformed into S bacteria.
This suggested a transfer of genetic material.

Designed and ran 4 Experiments

Four key experiments were conducted.
Live R cells did not cause pneumonia
Live S cells did cause pneumonia
Killed S cells did not cause pneumonia
Killed S cells plus live R cells DID cause pneumonia

What happened?

The possibility of R cells mutating was discussed.
The possibility of some S cells surviving was discussed.
It was concluded that DNA transferred and changed the R cells.

Later Studies

Further experiments used non-lethal forms of strains to infectious ones.
Early belief was that proteins were hereditary.
Biochemical experiments showed strains with protein digesting enzymes still developed more proteins.
Experiments with DNA digesting enzymes showed cell functionality stopping.
These affirmed DNA as the hereditary molecule.

Viruses

In 1952, molecular biologists studied bacteriophages (viruses that infect bacteria).
Electron micrographs showed viruses had protein coats and nucleic acids inside.
When viruses infect cells, the protein coat remained outside, while nucleic acids entered.

The structure of DNA

Rosalind Franklin used X-ray crystallography to study DNA structure.
X-ray diffraction patterns revealed the DNA molecule's structure.
Watson and Crick used Franklin's data and made significant deductions.

Fame and Fortune

Watson and Crick received the Nobel Prize.
Rosalind Franklin, who did much of the foundational work, was not recognized.

DNA

DNA is a very stable molecule with a double helix structure that's more stable than RNA.
Each gene codes for one protein.
Genes are composed of 4 nucleotides: adenine, thymine, guanine, and cytosine.
The sequence of nucleotides is the genetic code, determining protein structure.
Nucleotides form codons of three, each specifying specific amino acids.

DNA Structure

DNA is double-stranded and helical, adding stability.
Base pairs (A-T, G-C) are complementary.
Two hydrogen bonds link A and T.
Three hydrogen bonds link G and C.
The sugar-phosphate backbone forms the DNA’s structure.

Nucleotides

Pyrimidines are single rings.
Purines are double rings.
DNA's structure is like a ladder — a pyrimidine pair bonded to a purine.

DNA Backbone Structure

Nucleotides are bonded together via phosphodiester bonds.
The phosphate groups of nucleotides form the DNA backbone.
Phosphate groups are negatively charged, so the backbone aligns on opposite sides.

RNA

DNA is the blueprint. RNA is the worker.
Three main types of RNA:
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
All RNA is manufactured in the nucleus of eukaryotes or the nucleoid region of prokaryotes.

RNA and DNA Comparison

DNA: Deoxyribose sugar, contains thymine, double-stranded double helix, genetic material for most organisms.
RNA: Ribose sugar, contains uracil, instead of thymine, single-stranded, genetic material for some viruses.

Basic DNA to Protein Scheme

DNA—Transcription—RNA—Translation—Protein

Transcription

DNA information is converted into RNA information.
The "alphabet" is the same -- just the "letters" (nucleotides) differ (Thymine → Uracil)

Translation

mRNA's information is converted to protein.
Codons on mRNA are converted into amino acids form the protein by translating the genetic alphabet.

mRNA

Messenger RNA carries genetic information from DNA to ribosomes
Accounts for 5-10% of the total RNA in a cell at any given point
Consists of a chain of nucleotides
Used for protein production but is temporary.

rRNA

Used in constructing ribosomes.
Ribosomes contain primarily rRNA and some proteins;
rRNA makes up 60-65% of the ribosome mass and proteins make up roughly 35-40%.
rRNA constitutes 75-80% of the total RNA in a cell at any given moment.

Ribosome Structure

Ribosomes have a small and a large subunit
Involved in assembling amino acids according to mRNA instructions.

Promoter

Transcription begins at a region called a promoter
RNA polymerase recognizes the specific promoter region to start transcription
Promoters are found upstream (before) the gene to be transcribed.

RNA Polymerase

Responsible for mRNA synthesis, based on a DNA template
There are specific RNA polymerases for different RNA types: -RNA Polymerase I (rRNA) -RNA Polymerase II (mRNA)
-RNA Polymerase III (tRNA)

Construction of RNA

RNA polymerase uses a DNA template and environmental nucleotides to build RNA molecules.
The template is a particular strand of DNA, selected with a promoter.

mRNA

Post-transcriptional processing adds a "cap" and "tail" to the finished mRNA.
This modified mRNA is transported outside the nucleus toward ribosomes for protein synthesis.
"Tail" protects the mRNA from enzymatic degradation.

Junk DNA

DNA contains portions that are not coding for protein.
Exons code for proteins.
Introns are non-coding regions that are spliced out.
Introns can create alternative mRNA versions allowing for many proteins from a single gene.

Genetic Code

The genetic code uses triplets of nucleotides (codons) to specify amino acids.
AUG codes for methionine (start codon).
UAA, UAG, and UGA are stop codons.

tRNA

tRNA molecule carries amino acids to the ribosome.
They contain specific anti-codons that recognize mRNA codons.
The anticodon sequence determines which amino acid is attached to the tRNA.

Ribosomes

Ribosomes are the protein synthesis machinery, binding mRNA and tRNA molecules
The ribosome functions to orient the mRNA and tRNA in relation to one another so they can bond effectively, effectively acting as an enzyme.

Translation (Stages)

Initiation: start codon, mRNA and tRNA, assembly of ribosomal units.
Elongation: tRNA brings in amino acids to each codon on mRNA.
Termination: stop codon reached, release of amino acid chain.

Mutations and Proteins

Changes in DNA sequences (mutations) may affect protein formation.

Point Mutations

Changes in one or a few base pairs.
Substitution mutations: replacing one nucleotide with another.
Insertion/deletion mutations: adding or removing nucleotides, which causes a major structural change.

Mutagens

External factors causing mutations (U/V light, chemicals).
Recent research shows high diversity in surface oceans and organisms.
Limited diversity in deep-earth organisms, suggestive of a slower rate of evolution in such an environment.

Mutations important for evolution

Mutations introduce variation, which allows organisms to adapt over generations and develop useful metabolic processes and body structures.
Gene replication in the genome allows for multiple copies of genes to evolve over generations without interfering with the primary function.

Some Examples of Mutations

Single base-pair changes can lead to significant differences, as evidenced in the evolution of birds' beaks and fruit flies' development.

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Description

Explore the fundamentals of DNA and proteins, and how early theories of heredity evolved over time. Learn about key experiments by Frederick Griffith that unveiled the role of DNA in genetic material transfer and its implications for understanding heredity.