Biology Chapter 12: DNA and RNA
Terms in this set (75)
Fredrick Griffith's Experiment and Transformation
1928, British Scientist looked at how bacteria caused pneumonia.
Isolated two different strains from mice and grew each in culture plates.
One caused pneumonia, one was harmless. The two strains were easy to distinguish between.
Griffith wondered if the disease-causing bacteria produced a poison.
Pneumonia-causing strain of bacteria
Cultured strain of pneumonia-causing bacteria that grew into smooth colonies on the culture plates.
When injected into the mice it caused death.
Harmless strain of bacteria
Cultured strain of harmless bacteria, that did not cause pneumonia, that produced colonies with rough edges on the culture plates.
When injected into the mice it was harmless.
Heat-killed pneumonia-causing strain of bacteria
Heat-killed cultured strain of pneumonia-causing bacteria that was harmless.
This suggested that the disease-causing bacteria did not release a chemical poison.
Process in which one strain of bacteria is changed by genes from another strain of bacteria.
Transformation of strains of bacteria
Mixture of heat-killed disease-causing bacteria with the live, harmless bacteria resulted in the live, disease-causing bacteria found in the lungs of dead mice.
Griffith hypothesized that some factors were transferred from the heat-killed cells into the live cells.
This factor must contain information that could transform bacteria. The factor may be a gene because the resulting disease-causing bacteria may have been inherited by the transformed bacteria's offspring.
Avery's Repeated Experiments and DNA
1944, Avery and group at Rockefeller Institute in New York repeated Griffith's work to determine which molecule was most important for transformation to occur.
Made an extract from heat-killed bacteria and treated with enzymes that destroyed proteins, lipids, carbohydrates, and later, RNA. Since the transformation occurred, these molecules were not responsible.
Avery and other scientists discovered that nucleic acid, DNA, stores and transmits genetic information from one generation to the next. DNA is the transforming factor.
1952, Hershey and Chase collaborated in studying viruses. Very important to understand the chemical nature of genes.
Grew viruses in cultures containing radioactive isotopes to use as markers. Phosphorus-32 for DNA injected and Sulfur-35 for protein injected. 32P was found.
Hershey and Chase concluded genetic material of bacteriophage was DNA, not protein.
Nonliving particle smaller than a cell that can infect living organisms.
Type of virus that infects bacteria. "Bacteria eater".
Composed of DNA/RNA core and a protein coat.
Enters bacteria, attaches to surface of cell, injects genetic information. Viral genes act to produce many bacteriophages and gradually destroy the bacterium. When the cell splits open, hundreds of new viruses burst out.
Radioactive markers are used to determine which part of the virus entered the infected cell, the DNA core or protein coat, to find whether genes are made up of proteins or DNA.
Components and Structure of DNA
How DNA, or any molecule, can do the three critical things of genes that makes it special: 1. Carry information from one generation to the next. 2. Put that information to work to determine inheritable characteristics of organisms. 3. It is easily copied, all of the cell's genetic information is copied every time it divides.
"Backbone" of the DNA chain is formed by sugar and phosphate groups of each nucleotide.
Make up DNA. Three parts: deoxyribose molecule, phosphate group, and a nitrogen base.
Join together in any order making any sequence of bases possible.
Four different nucleotides strung together like letters of the alphabet make it possible to carry coded genetic information.
There are four different bases in DNA, purines: adenine and guanine, and pyrimidines: cytosine and thymine.
Stick out sideways from chain.
American biochemist discovered the percentage of guanine = the percentage of cytosine and the percentage of adenine = the percentage of thymine.
"Rule" A=T (form double hydrogen bonds) and G=C (form triple hydrogen bonds).
Remains despite differences amongst various organisms, the obey the rule.
Rosalind Franklin's work
1952, Franklin studies DNA molecules using x-ray diffraction to get information about the DNA molecule by concentrating powerful x-ray beams on treated samples and recording the scattering patter of x-rays on film and worked hard to improve the results.
Alone, the x-ray pattern does not reveal the structure of DNA but provides important clues: x-shaped pattern in photograph shows the strands in DNA twisted around each other, like coils of a spring, a "helix"; the angle of the 'x' suggests two strands in the structure' other clues suggest nitrogenous bases near the center of the molecule.
Watson and Crick's work
1953, Watson and Crick develop double-helix model of the structure of DNA by using a copy of Franklin's x-ray pattern, photo 51, which explained the puzzle of how DNA could carry genetic information and how it could be copied.
Watson and Crick's model of DNA was a double-helix in which two strands were wound around each other, similar to a twisted ladder or staircase.
The structure accounts for many of the features in the x-ray pattern, but did not explain what forces held the two strands together.
Discovered hydrogen bonds could form between certain nitrogenous bases and provide just enough force to hold the strands together.
Principle that shows that hydrogen bonds can only form between certain base pairs: adenine and thymine / guanine and cytosine.
This explained Chargaff's rule because it is the reason A=T and G=C, for every one base pair on the double-helix there is its base pair.
DNA is easy to extract and analyze, it is present in large amounts in many tissues.
DNA is very long.
DNA in Prokaryotic Cells
In prokaryotic cells, the DNA is known as the "cell's chromosome" as it is a single circular DNA molecule found in the cytoplasm and contains nearly all of the cell's genetic information.
DNA in Eukaryotic Cells
In eukaryotic cells, the DNA is more complicated. It contains up to 1,000 times the amount of DNA as prokaryotes, it is not found free in the cytoplasm but in the nucleus in the form of a number of chromosomes. The number of chromosomes vary by organism.
Chromosome (DNA) of E. Coli
E Coli is a prokaryote that lives in the human colon, the large intestine. It has 4,639,221 base pairs and has a length of 1.6mm, all of which fits within the bacterium. For the DNA to fit inside the typical bacterium, it must be folded into a space 1/1000th of its length.
Chromosome Structure in Eukaryotic Cells
DNA in eukaryotic cells is packed more tightly. The human cell contains 1,000 times the number of base pairs of DNA as a bacterium. The DNA of a human cell is one meter long and fits within the nucleus because of the composition of eukaryotic chromosomes. Chromosomes contain DNA and histones, a protein. During mitosis, fibers of each individual chromosome are drawn together to form tightly packed chromosomes, visible in all dividing cells using a light microscope. The tightly packed nucleosomes may help separate the chromosomes during mitosis. Mistakes in DNA foldings could harm the cell's ability to reproduce.
Substance formed by tightly packed DNA and histones, a protein. The DNA is tightly coiled around histones to form a beadlike structure, a nucleosome. Nucleosomes pack with one another to form a thick fiber, shortened through loops and coils. During most of the cell cycle, the fibers are dispersed throughout the nucleus and individual chromosomes are not visible. Some evidence supports that changes in chromatin structure and histone-DNA binding is associated with changes in gene activity and expression.
A beadlike structure formed from DNA tightly coiled around histones. The function of the nucleosome is to fold enormous lengths of DNA into the tiny space available inside the nucleus.
Histones are a protein. The function of histones has changed little during evolution.
Watson and Crick's discovery of the double-helix structure of DNA explained how DNA could be replicated. Each strand of DNA has all of the information needed to reconstruct the other half by the mechanism of base pairing, making the strands complimentary to one another. If separated, the rules of base paring allow one to reconstruct the base sequence of the other strand.
DNA replication in prokaryotic cells
In most prokaryotes, DNA replication begins at a single point a the chromosomes and often proceeds in two directions until the entire chromosome has been replicated.
DNA replication in eukaryotic cells
In eukaryotic chromosomes, larger than that of a prokaryote, DNA replication occurs at hundreds of places at once and proceeds in both directions until each chromosome is completely copied.
The sites where separation and replication occur.
The process of duplicating DNA:
The two strands separate and replication forks form.
As each new strand forms, new bases are added, following the rules of base pairing.
The result is two DNA molecules identical to each other and the original. Each resulting DNA molecule has one original strand and one new one.
The copying process of DNA before a cell divides. Replication ensures that each resulting cell will have a complete set of DNA molecules.
During DNA replication, the DNA molecules separate into two strands, then produce two new complementary strands following the rules of base pairing. Each strand of the double-helix of DNA serves as a template for the new strand.
How replication occurs
Replication is carried out by a series of enzymes that "unzip" the molecule of DNA, which occurs when the hydrogen bonds are broken and the two strands of the double-helix structure unwind. Each strand serves as a template for the attachment of complementary bases.
The double-helix structure of DNA explains how it can be copied but is not how a gene works.
DNA polymerase is the principal enzyme involved in DNA replication. It joins individual nucleotides to produce a DNA molecule, a polymer. It "proofreads" each new strand of DNA to maximize the odds of each molecule being a perfect copy of the original.
A gene is coded DNA instructions and controls the production of proteins with a cell. Decoding genes (genetic messages): It copies part of a nucleotide sequence from DNA into RNA.
Genes contain nothing more than instructions for assembling proteins.
The gene that codes for the enzyme to produce pigment or production of red blood cells can control the skin color or blood type.
RNA contains the coded information for making proteins. The RNA molecule is the disposable copy of a segment of DNA. RNA is the working segment of a single gene. The ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds or thousands of RNA molecules.
Structure of RNA
RNA is similar to DNA, it is a long chain of nucleotides. It is made up of a 5-carbon sugar, a phosphate group, and nitrogenous bases.
Differences between RNA and DNA
Sugar: the sugar in RNA is ribose and the sugar in DNA is deoxyribose, containing one less sugar.
Structure: RNA is single stranded and DNA is a double-helix.
Nitrogenous Base: RNA contains uracil in place of thymine found in DNA.
Types of RNA
The function of the majority of RNA molecules is protein synthesis. RNA controls the assembly of amino acids into proteins. The three main types of RNA are mRNA, rRNA, and tRNA.
mRNA carries copies of instructions for assembling amino acids into proteins. It serves as a "messenger" from DNA to the rest of the cell.
rRNA, along with several dozen other proteins, makes up ribosomes, where proteins are assembled.
tRNA transfers each amino acid to the ribosome as it is specified by coded messages in the mRNA during the construction of a protein.
Transcription is the first step in gene expression in which a particular part of the nucleotide sequence DNA is copied into a complementary sequence in RNA by the enzyme, RNA polymerase.
Transcription produces RNA molecules and occurs in the nucleus.
The process: RNA polymerase binds to DNA and separates its strands. RNA polymerase uses one strand as a template from which nucleotides are assembled into a strand of RNA.
RNA polymerase is the enzyme required for transcription and is similar to DNA polymerase.
Prompters are the region DNA by which RNA polymerase binds to. It has signals in the DNA that indicate to the enzyme where to bind to in order to produce RNA. Similar signals in DNA cause transcription to stop when the new RNA molecule is complete.
The RNA molecule is produced by copying DNA. Introns and exons are sequences of nucleotides. When the RNA molecules form, both introns and exons are copied from the DNA. Introns are cut out of the RNA molecules while it is still in the nucleus. The remaining exons are cut and spliced back together to form the final mRNA.
Introns and exons allow for very small changes in the DNA sequence which can have dramatic effects on gene expression, playing a role in evolution.
The remaining question is why cells use the energy to make a large mRNA and throw away parts of it.
Introns are sequences of nucleotides in the DNA of eukaryotic cells that are not involved in coding for proteins. Introns are cut out of the copied RNA while still in the nucleus.
Exons are sequences of nucleotides in the DNA that code for proteins. Exons are "expressed" in the synthesis of proteins. In the copied RNA, exons are cut and spliced back together to form the final mRNA. Some exons are cut and spliced in different ways in different tissues which makes it possible for a single gene to produce several different forms of RNA.
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product, often proteins.
Proteins are made by joining amino acids into long chains called polypeptides. The properties of proteins are determined by the order in which the different amino acids are joined together to produce polypeptides.
Proteins have everything to do with genes.
Many proteins are enzymes that catalyze and regulate chemical reactions.
Proteins are microscopic tools, each specifically designed to build and operate components of a living cell.
Polypeptides are the polymer of the monomers amino acids. Polypeptides contain combinations of any or all of the twenty different types of amino acids. Polypeptides determine the properties of the proteins they produce by the order which the different amino acids join together. The particular order of nitrogenous bases in DNA and RNA is translated into a particular order of amino acids in the polypeptide.
The genetic code is the "language" of mRNA instructions. It is written through the four "letters" of the four different nitrogenous bases. The code with four letters carries the instructions for the twenty different amino acids. The code is read three letters at a time, making each "word" three letters long.
A codon consists of three consecutive nucleotides that specify a single amino acid that is added to the polypeptide. Codons represent the different amino acids. The four bases make 64 possible three base codons (4 cubed).
Some amino acids are specified by more than one codon.
AUG specifies methionine, which serves as the initiation codon for protein synthesis.
There are three different "stop" codons, that act as a period at the end of a sentence and signify the end of a polypeptide.
Translation is the decoding of mRNA into a polypeptide chain.
Translation takes lace on the ribosome.
During translation, the cell uses information form mRNA to produce proteins.
Process of translation
1. The mRNA is transcribed in the nucleus, once it enters the cytoplasm and attaches to the ribosome, translation begins. 2. Each tRNA has an anticodon, and the ribosome positions the start codon to attracts its anticodon. The ribosome also binds the the next codon to its anticodon. 3. The ribosome joins two amino acids and breaks the bond between them and its tRNA floats away, from ribosome to ribosome to bind another tRNA. The ribosome moves along mRNA, binding to new tRNA and amino acids. 4. The process continues until the ribosome reaches one of three stop codons, resulting in a complete polypeptide.
Roles of DNA and RNA
DNA is the "master plan", and remains safely within the nucleus, and used to prepare the RNA "blueprints", which go to the protein-building sites, the ribosomes.
Mutations are changes in genetic material and are a mistake in the copying of DNA.
Gene mutations produce changes in a single gene. Types of gene mutations include: point mutations, substitutions, insertions, deletions, and frameshift mutations.
Chromosomal mutations cause changes in a the number or structure of whole chromosomes. The location of genes on a chromosome change the number of copies of some genes.
Types of chromosomal mutations include: deletions, duplications, inversions, and translocations.
Point mutations (genetic mutation)
Genetic point mutations are a gene mutation involving changes in one or few nucleotides. They occur at a single point in the DNA sequence. They include substitutions, insertions, and deletions.
Substitutions (genetic mutation)
Genetic substitutions occur when one base is changed to another. They usually affect no more than a single amino acid.
Insertions (genetic mutation)
Genetic insertions occur when an extra base is inserted to a sequence. The effects are more dramatic because the genetic code is read in three-base codons and one extra base causes every codon that follows to be shifted.
Deletions (genetic mutation)
Genetic deletions occur when a base is removed from a sequence. The effects are more dramatic because the genetic code is read in three-base codons and one less base causes every codon that follows to be shifted.
Frameshift mutations are caused by indels (insertions or deletions) and shift the "reading frame" of a genetic message because every amino acid that follows the point of mutation is shifted. They can alter a protein so much that it is unable to perform its normal function.
Deletions (chromosomal mutation)
Chromosomal deletions involve the loss of all or part of a chromosome.
Duplications (chromosomal mutation)
Chromosomal duplications produce extra copies of parts of a chromosome.
Inversions (chromosomal mutation)
Chromosomal inversions reverse the direction of parts of a chromosome.
Translocations (chromosomal mutation)
Chromosomal translocations occur when part of one chromosome breaks off and attaches to another.
Significance of Mutations
Most mutations are neutral although some are dramatic.
Mutations are the source of genetic variability in a species and may be beneficial or harmful.
Neutral mutations have little or no effect on the expression of genes or the function of proteins for which they code.
Dramatic mutations include changes in protein structure or gene activity and are often harmful because defective proteins disrupt normal biological activities.
Harmful mutations are the causes of genetic disorders, cancers, etc.
Beneficial mutations produce proteins with new or altered activities and can be useful to organisms in different or changing environments.
Polyploidy (chromosomal mutation)
Polyploidy is a condition in which an organism has extra sets of chromosomes. In plants, it can make them larger and stronger than a diploid.