Chapter 12: DNA
Terms in this set (37)
the four nitrogenous bases
adenine, thymine, guanine, and cytosine
thymine pairs with...
guanine pairs with...
what are the three parts of a nucleotide?
phosphate, deoxyribose sugar, nitrogen-containing base
what kind of sugar is found in a nucleotide?
what part(s) of the nucleotides make up the rungs of the "ladder"?
what parts of the nucleotides make up the sides (backbone) of the "ladder"?
phosphate and deoxyribose
how many hydrogen bonds connect thymine and adenine together?
how many hydrogen bonds connect cytosine and guanine together?
(example of strand) ATCCAGCGT
what rule is used to join the free nucleotides to the exposed bases of the DNA?
complementary base-pair rule
why is DNA replication called semi-conservative?
it breaks in HALF when it replicated KEEPING part of its original self
nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds
slightly acidic molecules originally identified in cell nuclei
made up or three basic components (5-carbon sugar--deoxyribose--, phosphate group, and nitrogenous base--adenine-A-thymine-T-guanine-G-cytosine-C-can be in any sequence)
avery and other scientists discovered that NUCLEIC ACID DNA STORES AND TRANSMITS GENETIC INFORMATION FROM ONE GENERATION TO THE NEXT need to understand the chemical nature of the gene to further our understanding of genetics (this began with Griffith)
only one of the strains caused pneumonia (the S strain was the disease-causing bacteria and the R strain was the harmless bacteria) he injected both into mice, the mouse injected with the S strain died and the mouse injected with the R strain lived heated disease causing strain meant the mouse lived when he mixed heat-killed S-strain bacteria with live, harmless bacteria from the R strain the mouse died (awe poor mouse)
called this TRANSFORMATION because one type of bacteria had been CHANGED PERMANENTLY into another because the ability to cause disease inherited, griffith concluded that the transforming factor had to be a gene
avery and his team extracted a mixture of various molecules from the heat-killed bacteria then treated the mixture with enzymes that destroyed PROTEIN, LIPIDS, CARBOHYDRATES, and some other molecules, including the NUCLEIC ACID RNA
the role of DNA
the DNA that makes up genes must be capable of STORING, COPYING, TRANSMITTING genetic information
the structure of DNA
erwin chargaff discovered that the percentages of adenine (A) and thymine (T) bases AND guanine (G) and cytosine (C) were almost equal in any sample of DNA the observation that A=T and G=C became known as one of "chargaff's rules" of base pairing
(1950s) rosalind franklin used a technique called x-ray diffraction to uncover information about DNA's structure an x-shaped pattern was discovered (showed that the strands in DNA are twisted around each other like the coils of spring) other clues suggest that the nitrogenous bases are near the center of the DNA molecule
watson and crick
james watson and francis crick were also trying to understand the structure of DNA early in 1953, watson was shown a copy of franklins x-ray pattern the clues in franklin's x-ray pattern enabled them to correctly build a model that explained the specific structure and properties of DNA
double helix model
the two strands run antiparallel and twist around each other like spiral staircases model explains chargaff's rule of BASE PAIRING and how the two strands of DNA are held together the double helix accounted for franklin's x-ray pattern nucleotides meet in the middle of the structure allowing each strand to carry a sequence of nucleotides
watson and crick discovered that hydrogen bonds form between nitrogenous bases, providing just enough force to hold the two DNA strands together hydrogen bonds are weak and allow the two strands of the helix to separate the ability of the two strands to separate is critical to DNA's functions
unwinds the DNA to produce the single strand (where the replication bubble and replication fork are formed)
single-strand binding proteins
hold the single strand of DNA in place while replication occurs
an enzyme that joins individual nucleotides to produce a new strand of DNA (also "proofreads" each new strand of DNA, ensuring that each molecule is a perfect copy of the original)
starts off the 5' to 3' direction on the lagging strand
extra enzyme to help replication of DNA
short DNA formed on the lagging strand during the process of DNA replication
the tips of chromosomes
copying the code
DNA replication in the S phase of interphase before mitosis
All new cells produced through mitosis must have a complete copy of the organism's DNA
The process of DNA replication is SEMI-CONSERVATICE (meaning half is original DNA--template strand--and half is "new" DNA that is laid down; remember that DNA runs antiparallel from the 5' to the 3' end--has to do with the chemical orientation of the carbon deoxyribose molecule)
Base pairing in the double helix explained how DNA could be copied, or replicated, because each base on one strand pairs with only one base on the opposite strand each strand of the double helix has all the information needed to reconstruct the other half by the mechanism of base pairing because each strand can be used to make the other strand, the strands are said to be complementary
what role do enzymes play in DNA replication?
DNA helicase unwinds the DNA to produce the single strand
Single-strand binding proteins hold the single strand of DNA in place while replication occurs
DNA polymerase can only read of 3' to 5'
The other strand is called the lagging strand because it cannot add nucleotides to the 5' end and therefore replication is much slower RNA primase is set and nucleotides attach to it, then the DNA polymerase can run in the proper direction (3'-5') Okazaki fragments are formed and new stretches of DNA are on pieces that need to be cleaned up and organized--this is completed by DNA ligase
the replication process
Before a cell divides, it duplicates its DNA in a copying process called replication
This process ensures that each resulting cell has the same complete set of DNA molecules
During replication, the DNA molecule separates into two strands and then produces two new complementary strands following the rules of base pairing each strand of the double helix of DNA serves as a template, or model, for the new strand
The two strands of the double helix separate, or "unzip," allowing two replication forks to form as each new strand forms, new bases are added following the rule of base pairing the result of replication is two DNA molecules identical to each other and to the original molecule each DNA molecule resulting from replication had one original strand and one new strand
the role of enzymes
DNA replication is carried out by a series of enzymes; they first "unzip" a molecule of DNA by breaking the hydrogen bonds between base pairs and unwinding the two strands of the molecule
Each strand then serves as a template for the attachment of complementary bases the principle enzyme involved in DNA replication is DNA polymerase
replication in living cells
Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied in eukaryotic cells, replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied
The cells of most prokaryotes have a single, circular DNA molecule in the cytoplasm, containing nearly all the cell's genetic information eukaryotic cells, on the other hand, can have up to 1000 times more DNA; nearly all of the DNA of eukaryotic cells is found in the nucleus