Prentice Hall Biology Chapter 12
DNA & RNA
Terms in this set (50)
what did Oswald Avery's experiments show?
The nucleic acid DNA stores and transmits genetic information.
virus that eats other bacteria cells
How did the Hershey-Avery experiment conclude that genetic material was DNA and not protein?
Traces of phosphorus marker were found inside the bacteria which were mixed with the viruses grown in the radioactive phosphorus and sulphur mix.
what are the three critical things that genes are known to do?
1. carry information from one generation to the next
2. put that information to work by determining the heritable characteristics of organisms
3. had to easily be copied because all of a cell's genetic information is replicated every time the cell divides
DNA is made up of what units
what is a nucleotide made up of?
1. a 5-carbon sugar called deoxyribose
2. a phosphate group
3. nitrogenous (nitrogen containing) base
what kinds of nitrogenous bases exist in DNA?
1. adenine and guanine - both belong to group of compounds called purines
2. cytosine and thymine - both belong to a group of compounds called pyrimidines
what is the main difference between purines and pyrimidines
purines have two rings in their structures; pyrimidines have one ring in their structures
what is the structure of a nucleitide
1. a deoxyribose molecule or more generally a 5-carbon sugar
2. a phosphate group
3. a nitrogenous base
What are Chargaff's Rules?
In any sample of DNA from any organism
1. percentage of adenine and thymine bases are almost equal
2. percentage of guanine and cytosine bases are almost equal
what is base pairing
the principle that bonds in DNA can only form between
1. adenine and thymine bases
2. guanine and cytosine bases
This explains Chargaff's rules
what is structure of DNA
Double helix in which two strands are wound around each other.
Each strand is made up of nucleotides
The two strands are held together by hydrogen bonds between adenine and thymine and between guanine and cytosine.
What do nucleosomes do?
Seem to be able to fold enormous lengths of DNA into the tiny space available in the cell nucleus.
Protein molecule around which DNA is tightly coiled inside chromatin.
Why are DNA strands said to be complementary?
Because each strand can be used to make the other strand. The rules of base pairing allow the base sequence of one strand to be used to create the other strand.
What is replication?
Process of duplicating DNA before a cell divides.
What are the steps of replication?
1. A DNA molecule separates into two strands.
2. Each of the two strands produces a new complementary strand following rules of base pairing.
What is the result of replication?
Two new DNA molecules, both identical to each other and to the original molecule.
What carries out replication?
A series of enzymes that 'unzips' the original DNA molecule, breaking the hydrogen bonds which connect the complementary base pairs.
What is the principal enzyme involved in DNA replication.
Where does prokaryotic and eukaryotic DNA reside inside the cell?
Prokaryotic - in cytoplasm, eukaryotic - in the nucleus
What is chromatin?
DNA molecules that are tightly coiled around proteins call histones.
What are Nucleosomes?
DNA and histone molecules which together form a bead-like structure.
How are nucleosomes organized?
Packed together to form a thick fiber shortened by a system of loops and coils.
What do nucleosomes do?
Seem to be able to fold enormous amounts of DNA into the tiny space available in the cell nucleus.
What are genes?
Coded DNA instructions that control the production of proteins within a cell.
List how RNA differs from DNA.
1. RNA has single strand.
2. Sugar used in RNA is ribose vs. deoxyribose in DNA.
3. RNA contains uracil instead of thimine.
What can an RNA molecule be thought of as?
A disposable working copy of a DNA segment, often a single gene.
Main job of RNA molecules.
Protein synthesis - the assembly of amino acids into proteins.
What are the 3 main types of RNA?
1. Messenger RNA
2. Ribosomal RNA
3. Transfer RNA
Messenger RNA (mRNA)
RNA molecule that carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell
Ribosomal RNA (rRNA)
type of RNA that makes up the major part of ribosomes, onto which proteins are assembled.
Transfer RNA (tRNA)
type of RNA molecule that transfers amino acids to ribosomes as it is specified by coded messages in mRNA during protein synthesis
How are RNA molecules produced?
Through a process called transcription.
What is transcription?
Process that produces RNA molecules by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA
What enzyme is used in transcription?
Describe what RNA polymerase do during transcription?
Binds to DNA and separates the DNA strands. It then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.
What is a promoter?
A region of DNA that indicates to an enzyme like RNA polymerase, where to bind to make RNA.
How does transcription stop when a new RNA molecule is complete?
When a signal, or specific base sequence similar to a promoter is found in the DNA sequence being copied.
sequences of nucleotides in DNA that are not involved in coding for a protein.
Sequences of nucleotides in DNA that are code for protein. They are called exons because they express the code for protein.
The removal of introns from newly synthesized RNA before the RNA can function. In addition the remaining exons are spliced together and caps are placed at each end of the new RNA molecule.
Possible functions of introns and exons
1. Splicing of a single gene in different ways for use in different tissues.
2. Evolution - small changes in DNA sequences causing big changes in gene expression.
A sequence of 3 nucleotides in an mRNA molecule. A codon specifies a single amino-acid that is to be added to the polypeptide chain.
decoding of a mRNA message into a polypeptide chain.
How many possible codons exist?
Since there exist 4 possible nitrogenous bases in DNA, and each codon consists of 3 nitrogenous bases, we have 4x4x4=64 possible codons.
What is the relationship between a gene and a codon?
A gene is a sequence of nucleotides in DNA which corresponds to a protein. During transcription, an mRNA molecule is generated with a sequence of nitrogenous bases which are complements of the ones in the original DNA nucleotides. The mRNA sequence of bases are grouped in sets of 3 bases, each set called a codon. Each codon corresponds to one of the amino-acids which will make up the polypeptide (or protein) through translation.
What is the start codon? What is its bases code.
The codon in mRNA which defines where translation will begin. Translation begins with the next codon. The start codon's bases code is AUG.
What is a stop codon? How many possible stop codons exist? What are their bases codes?
The codon in mRNA which defines where translation will end. The stop codon is not translated. Three possible stop codons exist. Their bases codes are UAA, UAG, UGA.
Describe the process of translation.
1. mRNA attaches to the ribosome and translation begins with the start codon.
2. Beginning with the start codon, a complementary (anti-codon) tRNA molecule, carrying an amino-acid is brought to the ribosome and attached to that codon. This releases the amino-acid, to be used in constructing a new polypeptide (protein). Then this tRNA molecule is released.
3. The ribosome advances through the mRNA molecule's codons, one by one, repeating the process above and attaching the new amino-acid to the chain of the previous ones.
4. Once it reaches the stop codon the process is ended, and the completed amino-acid chain, which is the new polypeptide, or protein, is released to the cell.