the molecular basis of inheritance (dna structure (dna is made up of…
the molecular basis of inheritance
dna is made up of molecules called nucleotides
nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. if you think of the double helix strcuture as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. the bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine.
each nucleotide contains a phosphate group
a sugar group and a nitrogen base
the order of nitrogen bases in a dna sequence forms genes, which in the language of the cell, tells cells how to make proteins
another type of nucleic acid, ribonucleic acid, or rna, translates genetic information from dna into proteins
four types of nitrogen bases are adenine (A), thymine (T), guanine (G), and cytosine (C).
dna molecules are long, that they can't fit into cells without the right packaging. to fit inside cells, dna is coiled tightly to form structures that are called chromosomes. each chromosome contains a single dna molecule. humans have pairs of chromosomes, which are found inside the cell's nucleus.
comparison of replication
it occurs inside the cytoplasm
there is single origin of replication
dna polymerase III carries out both initiation and elongation
dna repair and gap filling are done by dna polymerase I
rna is primer is removed by dna polmerase I
it occurs inside the nucleus
origin of replications are numerous
initiation is carried out by dna polymerase a while elongation by dna polymerase
the same are performed by dna polymerase
rna primer is removed by dna polymerase
steps of dna replication
replication fork formation - before dna can be replicated
replications begins; primer binding - the leading strand is the simplest to replicate
elongation - enzymes known as dna polymerases are responsible creating
termination - once both the continuous and discontinuous strands are formed
base substitutions - single base substitutions are called point mutations; two most common types of mutation are transition and transversion
transition - this occurs when a purine is substituted with another purine or when a pyrimidine is substituted with another pyrimidine
transversion - when a purine is substituted for a pyrimidine or a pyrimidine replaces a purine
deletion - resulting in a frameshift, results when one or more base pairs are lost from the dna. if one or two bases are deleted the translational frame is frame is altered resulting in a garbled message and nonfunctional product. a deletion of three or more bases leave the reading frame intact. a deletion of one or more codons results in a protein missing one or more amino acids.
insertions - additional base pairs may lead to frameshifts depending on whether or not multiple of three base pairs are inserted. combinations of insertions and deletions leading to a variety of outcomes are also possible
16.14 - addition of a nucleotide to a dna strand. dna polymerase catalyzes the addition of a nucleotide to the 3' end of a growing dna strand, with the release of two phosphates
16.15 - synthesis of the leading strand during dna replication. the diagram focuses on the left replication fork. dna polymerase III shaped like a cupped hand, is shown closely associated with a protein called the "sliding clamp" that encircles the newly synthesized double helix and then the sliding clamp moves dna polymerase III along the dna template strand
16.16 - synthesis of the lagging strand, which summarizes dna replication. this figure illustrates the steps in the synthesis of the lagging strand at one fork. whereas only one primer is required on the leading strand, each okazaki fragment on the lagging strand must be primed separately.
16.17 - a summary of bacterial dna replication. the left-handed replication fork of the replication bubble. viewing each daughter strand in its entirety, in the figure it shows that half of it is made continuously as the leading strand, while the other half is synthesized in fragments as the lagging strand.