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DNA and RNA
B.4.1
Nucleic acids
there are two types
- DNA- deoxyribose nucleic acids
- RNA - ribose nucleic acids
both are made of nucleotides that are made of three parts
a nitrogenous base
( C) - cytosine
(A) - adenine
( G) - guanine
(T) - thymine --- DNA only
( U)- uracil ---- RNA only
a simple (pentose) sugar
deoxyribose (DNA only)
ribose (RNA only)
a phosphate group
basic structure
DNA- contains two single chains which spiral around an imaginary axis to form
a double helix with nitrogenous bases from each strand of DNA chemically
bonded through the axis of the helix
● complimentary bases bond together
○ guanine to cytosine
○ thymine to adenine
RNA - consists of a single chain of nucleotides
● complimentary bases bond together
○ guanine to cytosine
○ uracil to adenine
DNA, Chromosomes, Genes
Protein Synthesis
the DNA carries the code for all genes in the organism
Genes are pieces of the DNA molecule that code for specific proteins
The process of making genes into proteins is called protein synthesis. Protein
assembly occurs in the ribosomes.
3 steps to protein synthesis:
1. DNA code of the gene segment is copied in the nucleus
2. the code is carried from nucleus into cytoplasm to ribosomes
3. the protein is then assembled and released from ribosome
these steps are carried out by the RNA
http://americanbookcompany.com/science/
Protein Synthesis - step 1- transcription
mRNA is made
- region of the DNA unwinds & separates (this segment is gene)
- unattached nucleotides in the nucleus are used to form a mRNA
strand
- the base uracil (U) matches the base adenine (A) instead of thymine
(T)
- the mRNA leaves the nucleus, goes into the cytoplasm, settles on the
ribosome surface
http://www.dnalc.org/view/15510-Transcription-DNA-codes-for-messenger-RNA-mRNA-3D-animation-with-basicnarration.html
transcription animation
protein synthesis- step 2- translation
mRNA is decoded and corresponding polypeptide is formed (a polypeptide is
made up amino acids) --- this happens at the ribosome
mRNA is chain of nucleotides- AUG ACA UUG CCA for example
*note that it is divided into 3’s- this is how the code is read
and each group of 3 is called a codon
each codon corresponds to a specific amino acid
tRNA (transfer RNA) brings amino acids that compliment each mRNA codon to
the surface of the ribosome where it is bound to the polypeptide chain that
forms the protein
a start codon signals the beginning of the polypeptide and when the stop codon
is reached, the ribosome releases the polypeptide chain as a protein into the
cell’s cytoplasm
translation animation
REMEMBER!
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protein synthesis begins with the manufacture of mRNA
Ribosomes are made of rRNA
proteins are made of polypeptide chains which are made of amino acids
transfer RNA (tRNA) carries amino acids to the ribosomes
the last step of protein synthesis is when the stop codon binds to the
ribosome and the polypeptide is released