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ArianaMejiaCh16-17 DNA and RNA molecule (DNA Replication (Prokaryotes…
ArianaMejiaCh16-17 DNA and RNA molecule
Dna
Structure
is made up of molecules called nucleotides.
Each nucleotide contains a phosphate group, a sugar group and a nitrogen base.
is a molecule that contains the instructions an organism needs to develop, live and reproduce.
stores instructions for making other large molecules, called proteins. These instructions are stored inside each of your cells, distributed among 46 long structures called chromosomes.
Components
A nucleotide contains adenine
T nucleotide contains thymine
G nucleotide contains guanine
C nucleotide contains cytosine
DNA Mutations
A mutation is a change in DNA, the hereditary material of life.
There are three types of DNA Mutations: base substitutions, deletions and insertions.
Base Substitution
Single base substitutions are called point mutations, recall the point mutation Glu -----> Val which causes sickle-cell disease. Point mutations are the most common type of mutation and there are two types.
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.
Deletions
A deletion, resulting in a frameshift, results when one or more base pairs are lost from the DNA (see Figure above). If one or two bases are deleted the translational 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. This may be deleterious or not.
3.Insertions
The insertion of additional base pairs may lead to frameshifts depending on whether or not multiples of three base pairs are inserted. Combinations of insertions and deletions leading to a variety of outcomes are also possible.
RNA
Structure
made up of a repeating strand of nucleotides, contains all 3 parts similar to DNA (sugar, phosphate, nitrogen base)
The sugar in RNA is called Ribose.
contains nitrogen base Uracil instead of Thymine. Uracil will bind to Adenine
RNA is single strand
RNA Splicing
is a process that removes the intervening, non-coding sequences of genes (introns) from pre-mRNA and joins the protein-coding sequences (exons) together in order to enable translation of mRNA into a protein.
The signal recognition particle (SRP)
is a ribonucleoprotein particle essential for the targeting of signal peptide-bearing proteins to the prokaryotic plasma membrane or the eukaryotic endoplasmic reticulum membrane for secretion or membrane insertion.
Polyribosome
a complex of ribosomes strung along a single strand of messenger RNA that translates the genetic information coded in the messenger RNA during protein synthesis.
tRNA and Structure
is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein.
tRNAs function at specific sites in the ribosome during translation, which is a process that synthesizes a protein from an mRNA molecule.
Transcription and Translation
Transcription
Transcription takes place in the nucleus. It uses DNA as a template to make an RNA (mRNA) molecule. During transcription, a strand of mRNA is made that is complementary to a strand of DNA.
Step 1: Initiation
Initiation is the beginning of transcription. It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands.
Step 2: Elongation
Elongation is the addition of nucleotides to the mRNA strand. RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs. There is a brief time during this process when the newly formed RNA is bound to the unwound DNA. During this process, an adenine (A) in the DNA binds to an uracil (U) in the RNA.
Step 3: Termination
Termination is the ending of transcription, and occurs when RNA polymerase crosses a stop (termination) sequence in the gene. The mRNA strand is complete, and it detaches from DNA.
Translation
Translation involves “decoding” a messenger RNA (mRNA) and using its information to build a polypeptide, or chain of amino acids. For most purposes, a polypeptide is basically just a protein (with the technical difference being that some large proteins are made up of several polypeptide chains).
Step 1: Initiation ("beginning"): in this stage, the ribosome gets together with the mRNA and the first tRNA so translation can begin
Step 2: Elongation ("middle"): in this stage, amino acids are brought to the ribosome by tRNAs and linked together to form a chain.
Step 3:Termination ("end"): in the last stage, the finished polypeptide is released to go and do its job in the cell.
DNA Replication
is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules.
Replication is an essential process because, whenever a cell divides, the two new daughter cells must contain the same genetic information, or DNA, as the parent cell.
Prokaryotes
occurs in the cytoplasm
only one replication fork is formed
only origin of replication per molecule of DNA
only have one origin of replication
replication occurs at the one point in each chromosome
Eukaryotes
occurs inside the nucleus
has multiple origins of replication
each origin of replication is formed of about 150 nucleotides
have many origins of replication in each chromosome
multiple replication forks
Steps
replication fork- the point where the DNA is opened up
enzyme DNA helicase opens one short segment of helix at a time.
-exposing its nitrogen bases
Double helix unwinds from histones
DNA polymerase molecules move along each strand
read the exposed bases
-matches complementary free nucleotides
5.the two separated strands of DNA are copied by separate polymerase molecules proceeding in opposite directions
Telomeres
They function to protect the ends of chromosomes from sticking to each other. They also protect genetic information during cell division because a short piece of each chromosome is lost every time DNA is replicated. Cells use a special enzyme called telomerase to keep dividing, which lengthens their telomeres.
