CHAPTER 9 DNA RNA MOLECULAR BIOLOGY

What is the role of DNA?

Store, copy, & transmit information.

What is storing information in relation to DNA?

Main job; molecule of heredity; controls patterns of development.

How does DNA copy information?

Before cells division (interphase & s phase); copies every gene.

How does DNA transmit information?

Each daughter cell must receive a complete set of DNA; careful sorting is important; if any is lost during meiosis, valuable information may be removed from one generation to the next.

What makes up DNA?

Nucleic acid (macromolecule) made of nucleotides joined into long chains by covalent bonds.

What is nucleic acid?

Slightly acidic molecule identified in the nucleus, which is made of long chains (polymer) of nucleotides (monomers).

What is nucleic acid made up of?

Deoxyribrose (5-C sugar), a phosphate group, and a nitrogenous base.

How are DNA chains formed?

By covalent bonds between the sugar of one nucleotide and the phosphate group of another.

What are the four kinds of nitrogenous bases that DNA possesses?

Adenine, Guanine, Cytosine, Thymine

How do nitrogenous bases sit on DNA?

They stick out sideways from the sugar and phosphate, and they can be arranged in ANY order.

What are purines, and which two nitrogenous bases are under this category?

They are two rings of N & C, and adenine (A) and guanine (G) belong to this category.

What are pyrimidines, and which two nitrogenous bases are under this category?

They are one ring of N & C, and cytosine (C) and thymine (t) belong to this category.

What is Chargaff’s Rule?

Discovered the % of A and T are almost equal, same goes for C & G. Therefore, A=T and C=G

What was the significance of Franklin’s X-Ray?

It revealed a twisted shape, which suggests TWO strands. It also shows how the nitrogenous bases are near the center.

Overall explanation of DNA.

Two strands are anti-parallel, which means the formation is a double helix. They are anti-parallel since the strands run in opposite directions, which allows bases to come into contact with eachother at the center.

What are nitrogen bases connected by?

Hydrogen bonds, which is represented by a dash between the letter. Example: A - T

Why are nitrogen bases connected by hydrogen bonds?

Because they provide just enough force to hold two strand together but weak enough to allow separation. Separation is necessary for replication during S phase, and hydrogen bonds are critical for DNA functioning.

Copying the code for DNA.

Each strand has all the information needed to reconstruct the other strand; based on base-pairing rules; strands are complementary.

What is the replication process for DNA?

Duplication of the DNA before cell division (S phase of interphase), which ensures daughter cells have a complete set of chromosomes. DNA is separated into two strands and produces two complementary strands.

What is step 1 for DNA replication?

2 strands unwind & are unzipped by a replication enzyme (DNA Helicase). This breaks H (hydrogen) bonds, which forms a replication fork.

What is step 2 for DNA replication?

Free nucleotides are added to each complementary strand. What is added is the enzyme : DNA polymerase. Also proofreads the new strand to ensure perfect copies.

What is the significance of the ending “ase”?

It tells you that you are dealing with an enzyme.

What is step 3 for DNA replication?

As nucleotides are added, DNA zips and rewinds back into a double helix. Each molecule has one new (complementary) strand and one old (parent strand; original).

Why can mistakes happen in DNA replication?

Because the tips of the chromosomes, which are known as telomeres, are difficult to copy. Therefore, DNA can be lost from telomeres over time.

What compensates for the problem of DNA being lost from telomeres over time?

The enzyme telomerase. This enzyme adds short repeating DNA sequences to telomeres, which lengthens the chromosome slights. Therefore, it makes it less likely that important sequences will be lost.

What is the difference between eukaryotic and prokaryotic replication?

Firstly, eukaryotic cells have a nucleus, whereas prokaryotic cells do not. In eukaryotic cells, DNA replication starts from multiple points, whereas prokaryotic DNA replication starts from a single point. Both cells DNA occurs in 2 directions. Lastly, in eukaryotic cells 2 copies remain close together until mitosis, whereas in prokaryotic cells 2 copies attach to the membrane for division.

What are the differences between DNA and RNA?

Both DNA and RNA are made of 5-carbon sugar, phosphate, and nitrogen base. However, DNA’s sugar is deoxyribrose, and RNA’s sugar is ribose. DNA is also a double strand helix, whereas RNA is a single strand. One of DNA’s nitrogenous bases is thymine, and in RNA instead of thymine, it’s uracil. Lastly, DNA is the master plan, whereas RNA is the blueprint.

What is the function of RNA?

Protein synthesis, which assembles amino acids into proteins.

What are the three types of RNA?

mRNA, rRNA, and tRNA

What is mRNA?

Messenger RNA; it carries copies of instruction to ribosomes, and it is a link between DNA + RNA in cytoplasm.

What is rRNA?

Ribosomal RNA; it makes up ribosomes along with 80 different proteins.

What is tRNA?

Transfer RNA; it transfers each amino acid to the ribosome as instructed by the mRNA.

Where does prokaryotic transcription take place?

In the cytoplasm.

Where does eukaryotic transcription take place?

In the nucleus and then moves to the cytoplasm.

What is RNA synthesis?

Segments of DNA serve as templates for complementary RNA (mRNA).

What is the first step of transcription?

RNA polymerase (ase-enzyme) binds to DNA at promoter and separates the DNA strands.

What is the promoter in DNA?

Regions of DNA that have specific base sequences; have a signal that shows RNA polymerase where to begin, with similar signals to indicate a stop.

What is the second step in transcription?

RNA polymerase uses one strand of DNA to assemble a complementary RNA strand.

Why is RNA edited?

Some portions of RNA are not used and need to be cut out before RNA can work properly.

What are introns?

Portions of the RNA that are cutout and discarded; they are removed before RNA leaves the nucleus.

What are exons?

Portions that are spliced back together for final mRNA strand; scientists are not 100% sure why this happens.

In editing RNA, different parts can be cut out to make

Different proteins.

RNA editing plays a role in

Evolution. This is because small changes have dramatic effects on how genes affect cellular function.

Prokaryotic gene regulation.

Proteins regulate genes by controlling transcription, and they do this by switching some genes on and other genes off. Genes are organized into operons, which are groups of genes that are regulated together.

What is the lac operon?

The three genes that must be turned on together before bacteria can use lactose. It is a compound made of two sugars (glucose and galactose).

If bacteria is in a medium where lactose is the only food source, what must it do?

It must transcribe the lac operon and produce these proteins. However, if another food source grows in, the lac operon is turned off.

On 1 side of operon are 2 regulatory regions. What are these two regions?

1st is a promoter (P), and it is the site where RNA polymerase binds to begin transcription. 2nd is an operator (O), which is the side where repressor protein binds to stop transcription.

Eukaryotic gene regulation.

Regulated at a number of levels; DNA-binding proteins regulate genes a transcription level, and are called transcription factors.

What are the different ways for eukaryotic gene regulation?

Some enhance transcription by opening chromatin. Some activate many genes at once. Some have multiple binding sites. Others form only in response to chemical signals. Others attract RNA polymerase. Others block access to genes. Each way influences the way a gene is transcribed.

Why is gene regulation important?

It shapes the development of multicellular organisms, which allows cells to differentiate and become specialized in structure and function.

What are homeotic genes?

They are a special group of genes that control the identity of body parts during the development of embryos. They are expressed in certain regions of the body.

What is the name of the very similar 130-base sequence that homeotic genes share?

Homeobox

What are the specific groups that identifies specific segments of the body called?

Hox genes, and they tell the body how to develop.

Environmental influence on gene regulation.

Factors such as temperature, salinity, and nutrition availability can influence gene expression. Metamorphosis can also moody expression responde to environment.

What is metamorphosis?

Involves a series of transformations from one life stage to another. It is regulated by internal and external factors.

What is the first step to decoding the genetic code?

Transcribe gene from DNA to mRNA (nucleus). DNA is then read in groups of three which are called codons. Each codon codes for a specific amino acid or stop/start.

What is the 2nd step to decoding the genetic code?

Codons are translated into proteins (macromolecules). Proteins are formed by joining amino acids together in long chains, called polypeptides. Specific amino acids & the order in which they are joined determines the properties of the protein, which influences the shape and determines the function.

Using the RNA bases, there are … possible codons.

64; the possible combinations consist of A, C, G, and U

Most, but not all, amino acids are specified by

More than one codon.

Why are there start and stop codons?

Because each gene has a starting and stopping point. RNA polymerase will continue to read codons until it reach 1 of 3 stop codons- UAA, UAG, UGA. These codons end translation.

AUG, codon with methionine amino acids is the

start codon for protein synthesis.

Where does translation occur?

Occurs in the cytoplasm on the ribosomes (rRNA). Uses the sequence of codons in the mRNA strand to assemble the polypeptide chain.

What is the first step of translation?

Begins when a ribosome attaches to an mRNA strand. Ribosome then reads each codon & signals a tRNA to bring the corresponding amino acid.

What is the 2nd step of translation?

Each tRNA has unpaired bases called anticodons, which are complementary to mRNA codons. Anticodons attach to the codon on the mRNA & deposit the amino acid to the growing chain.

What is step 3 of translation?

The ribosome moves down the mRNA strand to read the next codon & continue the process. At the same time, 1 bond is broken between codons and anticodons releasing the tRNA.

What is the 4th step of translation?

Chain continues to grow until ribosome reaches the stop codon. This releases the polypeptide chain, which completes translation.

What is the 5th step of translation?

mRNA strands are disassembled & nucleotides return to the nucleus.

Molecular basis of heredity.

Information in DNA is transferred to RNA then to proteins. Many proteins are enzymes that catalyze and regulate chemical reactions. Tools specifically designed to build or operate components of a living cell.

What is the universal code?

Genetic code. Although there are slight variations in amino acids assigned to specific codons, the code is always read as three bases in the same direction. Despite the enormous diversity in form and function, living organisms are remarkably united at the most basic level.

What are mutations?

Heritable changes in DNA, that are made by mistakes while copying DNA.

What are the two main categories of mutations?

Gene mutations, which are changes in a single gene. Chromosomal mutations, which are changes in a whole chromosome.

What occurs in gene mutations?

Changes in one or a few nucleotides (bases). Point mutation occurs at a single point in DNA sequence. It occurs during replication (S phase), and can be passed to every cell that develops from the original.

What is a substitution mutation?

When one base is changed into another. It affects a single amino acid, and can cause silent mutation. Can cause a missense mutation. And Lastly, can cause a nonsense mutation.

What affect does silent mutation have?

None at all.

What affect does missense mutation have?

Changes to new codon.

What affect does a nonsense mutation have?

Changes to a STOP codon.

What occurs in insertion and deletion mutations?

One base is inserted or deleted from DNA sequence, which shifts the reading frame. This is called a frame shift mutation, which changes every amino acid that follows and alters protein so much it cannot function properly.

What occurs in chromosomal mutations?

Changes in the number or structure of chromosomes, which changes both the location of genes on chromosomes and the number of copies of chromosomes.

What are the four types of chromosomal mutations?

Deletion, duplication, inversion, and translocation.

What occurs during deletion chromosomal mutation?

The loss of all or part of a chromosome.

What occurs during duplication chromosomal mutation?

Extra copy of all or part of a chromosome.

What occurs during inversion chromosomal mutation?

Reverses the direction of part of a chromosome, which is more common in insects.

What occurs during translocation chromosomal mutation?

One part of a chromosome breaks off and attaches to another non-homologous chromosome.

What are the effects of mutations?

Some have little to no effect, some are beneficial, and some negatively effect gene function.

What causes mutations?

Natural or artificial means. Natural is when there are errors in genetic process, or a stressful environment. Small changes in genes can accumulate over time and change the species. Artificial is mutagens, which are chemical or physical agents in the environment.

What are mutagens?

Chemical mutagens include pesticides, plant alkaloids, tobacco smoke, and environmental pollutants. Physical mutagens include electromagnetic radiation such as X-Rays and UV Rays.

What are the mutagen effects?

Can produce mutations at high rates. Can interfere with base-pairing, which increases error rate during replication. Can weaken DNA strands, causing breaks & inversions to produce chromosomal mutations. Cells can sometimes, however, repair damage, but if they don’t, the changes are permanent.

Are mutations harmful or helpful?

Depends on how DNA changes relative to each situation. Can be harmful due to disruption to normal function, but without mutations, organisms cannot evolve.

Mutations are the source of what?

Genetic diversity among species.

Large scale genetic changes for meiosis.

Recombination, non-disjunction, and polyploidy.

What is recombination?

Results from crossing over, and provides genetic diversity.

What is non-disjunction?

Occurs when homologous chromosomes or sister chromatids fail to separate during Meiosis.

What is polyploidy?

Nondisjunction of a full set of chromosomes, which results in triploid (3N) or tetraploid (4N).