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Questions and Answers

What are the components of DNA and its three-dimensional structure?

The components of a DNA molecule are nucleotides, composed of a deoxyribose sugar bonded to a phosphate and a nucleotide base (adenine, thymine, cytosine, or guanine). The three-dimensional structure of DNA is a double helix.

What evidence enabled Watson and Crick to decipher the structure of DNA?

The evidence included Rosalind Franklin's X-ray diffraction photo of a crystal of DNA, plus Erwin Chargaff's work that showed that DNA contains equal amounts of adenine and thymine and equal amounts of cytosine and guanine.

Identify the 3′ and 5′ ends of a DNA strand.

The 5' end has the 5th numbered carbon in deoxyribose facing out with a phosphate group attached, and the 3' end has the 3rd numbered carbon leading with an OH group attached.

What is the relationship between a gene and a protein?

A gene is a strand of DNA that encodes a protein. Signup and view all the answers

What are the two main stages in protein synthesis?

Transcription and translation. Signup and view all the answers

What are the three types of RNA, and how does each contribute to protein synthesis?

Messenger RNA (mRNA) carries DNA instructions for building protein, transfer RNA (tRNA) carries appropriate amino acids to the ribosome, and ribosomal RNA (rRNA) is a major component of ribosomes. Signup and view all the answers

What happens during each stage of transcription?

The steps of transcription are initiation, elongation of the RNA molecule, and termination. Signup and view all the answers

Where in the cell does transcription occur?

Transcription occurs in the nucleus. Signup and view all the answers

What is the role of RNA polymerase in transcription?

RNA polymerase uses the DNA template to bind additional RNA bases into the growing RNA chain. Signup and view all the answers

What are the roles of the promoter and terminator sequences in transcription?

The promoter signals the start of a gene, and the terminator signals the end of a gene. Signup and view all the answers

How is mRNA modified before it leaves the nucleus of a eukaryotic cell?

A cap is added to the 5' end, a poly A tail is added to the 3' end, and introns are removed while exons are spliced together. Signup and view all the answers

How did researchers determine that the genetic code is a triplet?

Researchers reasoned that the genetic code could not reflect 1-base or 2-base 'words' due to insufficient combinations for 20 amino acids, finding that a triplet code could encode for 64 possible combinations. Signup and view all the answers

What happens in each stage of translation?

The steps of translation are initiation, elongation of the polypeptide, and termination. Signup and view all the answers

Where in the cell does translation occur?

Translation occurs at ribosomes, which can be found free in the cytoplasm or attached to the rough ER. Signup and view all the answers

How are polypeptides modified after translation?

Polypeptides must be folded into proteins; sometimes amino acids are cut out, and sometimes multiple polypeptides join together. Signup and view all the answers

What are some reasons that cells regulate gene expression?

Cells regulate gene expression to avoid unnecessary protein production, saving energy. Signup and view all the answers

How do proteins determine whether a bacterial operon is expressed?

A repressor protein binds to an operator and prevents the genes in the operon from being transcribed. Signup and view all the answers

How do enhancers and transcription factors interact to regulate gene expression?

Transcription factors bind to certain DNA sequences to regulate transcription, while enhancers are sequences that help transcription factors enhance gene expression. Signup and view all the answers

What is an operon?

An operon is a stretch of DNA found in bacteria that controls gene regulation, comprising a promoter, an operator, and structural genes. Signup and view all the answers

What are some other ways that a cell controls which genes are expressed?

Cells can keep DNA coiled, attach methyl groups, splice out different introns, or degrade mRNA and proteins. Signup and view all the answers

What is a mutation?

A mutation is a change in the DNA sequence of a cell. Signup and view all the answers

What are the types of mutations, and how does each alter the encoded protein?

Point mutations change one or a few base pairs; include substitutions, insertions, and deletions, each potentially altering the encoded protein. Signup and view all the answers

What causes mutations?

Mutations are caused by DNA replication errors, errors in meiosis, chromosome inversions and translocations, or exposure to chemicals or radiation. Signup and view all the answers

What is the difference between a germline mutation and a somatic mutation?

A germline mutation occurs in cells that will become sperm or egg cells; a somatic mutation occurs in a non-germline body cell. Signup and view all the answers

How are mutations important?

Mutations are used to learn how genes function, develop new crop varieties, trace virus evolution, and are important for evolution. Signup and view all the answers

How can the number of proteins encoded in DNA exceed the number of genes in the genome?

The genome can make 400,000 proteins from about 25,000 genes by changing which introns are removed prior to splicing together mRNA. Signup and view all the answers

List some functions of the 98.5% of the human genome that does not specify protein.

It encodes rRNA, tRNA, regulatory sequences, contains pseudogenes, transposons, and tandem repeats. Signup and view all the answers

What is recombinant DNA?

Recombinant DNA is the combined DNA from two or more organisms. Signup and view all the answers

Put the following in order from smallest to largest: nucleotide, genome, nitrogenous base, gene, nucleus, cell, codon, chromosome.

The order from smallest to largest is nitrogenous base, nucleotide, codon, gene, chromosome, nucleus, and cell. Signup and view all the answers

List the differences between RNA and DNA.

RNA has ribose sugar, uracil as a nitrogenous base, can be single-stranded, and can catalyze reactions; DNA has deoxyribose, thymine, is double-stranded, and cannot catalyze reactions. Signup and view all the answers

Define and distinguish between transcription and translation. Where in a eukaryotic cell does each process occur?

Transcription copies DNA into mRNA in the nucleus, while translation translates mRNA into proteins at ribosomes in the cytoplasm. Signup and view all the answers

List the three major types of RNA and their functions.

mRNA carries genetic information, rRNA forms the ribosome, and tRNA carries amino acids to the ribosome. Signup and view all the answers

A mouse's genome has 1500 olfactory genes encoding proteins that enable the animal to detect odors. List all of the ways that a mouse cell might silence the unneeded genes.

The cell can keep DNA coiled, attach methyl groups, splice out different introns, or degrade mRNA and proteins. Signup and view all the answers

Explain how a mutation in a protein-encoding gene, an enhancer, or a gene encoding a transcription factor can all have the same effect on an organism.

A mutation can lead to a non-functional protein, regardless of its location, blocking the expression of relevant traits. Signup and view all the answers

How can a mutation alter the sequence of DNA bases in a gene but not produce a noticeable change in the gene's polypeptide product?

A mutation may change a codon but result in the same amino acid due to codon redundancy. Signup and view all the answers

How do researchers create recombinant DNA and transgenic organisms, and what are some applications of this technology?

Restriction enzymes cut DNA at specific sites; fragments are joined by DNA ligase to create recombinant DNA, resulting in transgenic organisms. Signup and view all the answers

Why is protein production essential to cell function?

Cell structure and function depend on proteins, which are necessary for metabolic processes. Signup and view all the answers

Study Notes

DNA Structure and Components

DNA is composed of nucleotides, which include a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).
The three-dimensional structure of DNA is a double helix, resembling a twisted ladder.

Evidence for DNA Structure

Rosalind Franklin's X-ray diffraction provided crucial data about DNA's helical structure.
Erwin Chargaff's findings indicated equal amounts of adenine to thymine and cytosine to guanine.

DNA Strand Orientation

The 5’ end features the 5th carbon of deoxyribose with a phosphate group, while the 3’ end has the 3rd carbon leading with an OH group.

Genes and Proteins

A gene encodes the instructions to produce a protein.

Stages of Protein Synthesis

Protein synthesis involves two main stages: transcription (copying DNA to RNA) and translation (decoding RNA to synthesize proteins).

Types of RNA

Messenger RNA (mRNA) carries DNA's instructions.
Transfer RNA (tRNA) brings amino acids to ribosomes.
Ribosomal RNA (rRNA) forms a major part of ribosomes and helps in assembling amino acids.

Transcription Process

In transcription:
- Initiation begins with DNA unwinding and RNA polymerase binding.
- Elongation involves RNA polymerase synthesizing RNA by adding complementary nucleotides.
- Termination occurs when RNA synthesis completes and DNA reforms.

Location of Transcription

Transcription takes place in the nucleus of eukaryotic cells.

RNA Polymerase Function

RNA polymerase synthesizes RNA strands using the DNA template.

Promoter and Terminator Sequences

Promoters signal where transcription begins; terminators indicate where transcription ends.

mRNA Modification

Before leaving the nucleus, mRNA receives:
- A 5’ cap.
- A poly A tail at the 3’ end.
- Introns removed, with exons spliced together.

Genetic Code

The genetic code is a triplet code, with three nucleotides coding for one amino acid, allowing for 64 possible combinations.

Translation Process

Translation stages include:
- Initiation involves ribosomal subunits binding to mRNA.
- Elongation entails amino acids being added to the growing polypeptide chain.
- Termination ends with the release of tRNA upon reaching a stop codon.

Location of Translation

Translation occurs at ribosomes in the cytoplasm or on the rough endoplasmic reticulum.

Polypeptide Modification

After translation, polypeptides need folding, and may undergo cuts or combine with other polypeptides.

Gene Expression Regulation

Cells regulate gene expression to conserve energy and avoid unnecessary protein production.

Operon Regulation

Repressor proteins inhibit transcription by binding to operators in bacterial operons.

Enhancers and Transcription Factors

Transcription factors prepare promoters for RNA polymerase binding, while enhancers are sequences that facilitate or regulate transcription.

Definition of Operon

An operon consists of a promoter, an operator, and structural genes that control gene expression in bacteria.

Additional Gene Regulation Mechanisms

Gene expression can be controlled through DNA compaction, methylation, intron splicing, and mRNA degradation.

Mutation Overview

A mutation is a change in a DNA sequence, which can affect protein synthesis.

Mutation Types and Effects

Point mutations change one or a few bases, leading to missense (amino acid change), nonsense (stop codon), or silent mutations (no change).
Insertions and deletions can cause frameshift mutations, altering multiple amino acids.

Mutation Causes

Mutations may arise from DNA replication errors, meiotic crossing over mistakes, environmental factors, or radiation exposure.

Germline vs. Somatic Mutations

Germline mutations occur in reproductive cells affecting offspring, while somatic mutations happen in non-reproductive body cells.

Importance of Mutations

Mutations help understand gene functions, lead to crop varieties, trace evolutionary lineage, and are vital for evolution and diversity.

Protein Coding and Genes

Approximately 25,000 genes can produce around 400,000 proteins through alternative splicing of RNA.

Non-Coding DNA Functions

Non-coding regions encode regulatory RNA, pseudogenes, transposons, and repetitive sequences involved in genetic regulation.

Recombinant DNA Defined

Recombinant DNA combines DNA from two or more organisms for research or biotechnological applications.

DNA Structures by Size

The hierarchy of DNA structures: nitrogenous base, nucleotide, codon, gene, chromosome, nucleus, cell.

RNA vs. DNA Differences

RNA contains ribose and uracil; DNA has deoxyribose and thymine. RNA is single-stranded; DNA is double-stranded.

Transcription vs. Translation

Transcription creates mRNA from DNA in the nucleus; translation converts mRNA to protein at ribosomes in the cytoplasm.

Functions of Major RNA Types

mRNA specifies proteins; rRNA helps form ribosomes; tRNA transports amino acids to ribosomes.

Gene Silencing in Mice

Mice silence unneeded olfactory genes through DNA coiling, methylation, intron splicing, and mRNA degradation.

Effects of Mutations

Mutations in protein-coding genes, enhancers, or transcription factors can lead to the same loss of function by hindering translation.

Mutation and Gene Expression

Mutations can alter the nucleotide sequence without affecting protein function due to redundancy in genetic coding.

Recombinant DNA Technology

Researchers utilize restriction enzymes and DNA ligase to create recombinant DNA, facilitating the generation of transgenic organisms for various applications.

Importance of Protein Production

Proteins perform essential roles in cell structure, function, catalyzing reactions, and forming new membranes during cell division.

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