Upload
minna
View
44
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Chapter 12 Protein Synthesis. Central Dogma: DNA RNA Protein (the flow of genetic information). Gene Segment of a DNA molecule, which codes for specific messenger RNA (mRNA) molecule and controls a specific trait mRNA protein (enzyme which produces a trait) . B. DNA - PowerPoint PPT Presentation
Citation preview
Chapter 12Protein Synthesis
Central Dogma: DNA RNA Protein(the flow of genetic information)
A. Gene • Segment of a DNA
molecule, which codes for specific messenger RNA (mRNA) molecule and controls a specific trait
• mRNA protein (enzyme which produces a trait)
B. DNA• Nucleic acid molecule• Controls cell activities
(cytoplasm) by determining the types of proteins (enzymes), a cell synthesizes
• Genes “make a specific protein”
2 Processes Essential to Protein Synthesis
1. Transcription – “Making a blueprint”– Synthesis of
messenger RNA from a segment of DNA (gene)
– Occurs in the nucleus– Controlled by RNA
polymerase
RNA Processing: pre-mRNA mature RNA1. RNA splicing introns removed and exons joined
together (NOW: mRNA is a continuous coding sequence)a. INTRONS- non-coding segments of nucleic acids (lie b/t exons)b. EXONS- coding segments of DNA (will be translated into AA during translation)
2. 5’ cap added to 5’ end of mRNA addition of modified form of guanine nucleotide
3. Poly-A tail added 3’ end of mRNA 50-250 A nucleotides
RNA Processing
RNA Splicing
Cont. 2 Processes Essential to Protein Synthesis
2. Translation– “Reading the blueprint” – Process at the ribosome where by genetic code
is made into a specific protein– Involves mRNA ,the tRNAs and rRNAs
(Write this Down in Notes:Steps in Translation
1. mRNA attaches to ribosome2. tRNA carries a specific AA to ribosome
(anticodon on tRNA base-pairs with codon on mRNA)* At P site3’ UAC 5’ tRNA 5’ AUG 3’ mRNA (*start codon)
3. The next tRNA enters A site and peptide bond forms (via peptide transferase) with that AA and the growing polypeptide chain- tRNA at P site leave via E site
4. Protein synthesis continues on until stop codon is read
5. After translation has ended, polypeptide is released
Steps in Translation
a. Ribosomes “factory” for protein synthesisb. mRNA “blueprint” for protein (codon)c. tRNA carry a specific a amino acid (anticodon)d. Amino Acids 20 different types (raw materials)e. ATP energy to form peptide bondsf. Peptide transferase ribosomal enzyme, which forms peptide bonds between amino acids in specific tRNA g. Activating enzymes20 different type of enzymes which link the appropriate amino acid to specific tRNA
Translation
Cont. 2 Processes Essential to Protein Synthesis
• Genes in the nucleus control enzymes and other cell proteins
• Enzyme determines the cell type and all its chemical reactions
Translation
3 Kinds of RNA
• All RNA’s are made (transcribed) from DNA templates in nucleus
1. mRNA (messenger RNA) (RNA processing occurs before they leave the nucleus)a. Found in both nucleus and cytoplasmb. Transcribes (copies) DNA codes into mRNA codes (CODONS- triplets/ 64 total that codes for 20 AA)c. Leaves the nucleus and carries the message to the ribosomes out into the cytoplasmd. May attach to several ribosomes (polysome) e. Exists as a short single-stranded moleculef. Processing occurs in nucleus (cut/splice-cap/tail)
Polysomes
The Genetic Code
The Genetic Code
Questions?
1. How many codons would it take to code 5 amino acids?
2. How many nucleotides would it take to code 5 amino acids?
Cont. 3 Kinds of RNA2. tRNA (transfer RNA)
a. Found only in the cytoplasmb. Specific amino acid attached to one end of
tRNAc. 3 letter ANTICODON found at other end of
tRNAd. Anticodon of tRNA will match codes of
mRNAe. Brings specific amino acids into position at
ribosomef. Exists as a single strand cloverleafg. Processing occurs in cytoplasm (charging
needs ATP, activating enzymes specific amino acid)
***NOTE: mRNA & tRNA have
similar structure, but have different functions
Cont. 3 Kinds of RNA3. rRNA (ribosomal RNA)
a. Found only making up structure of ribosomes
b. Is the largest of all RNA molecules
c. mRNA will attach to rRNA of ribosome and begin process of building protein
d. Composed of RNA and proteine. Comes in 2 pieces 50s (larger)
and 30s (small)f. Processing occurs in the
nucleolus
Overview of Protein Synthesis
Chapter 12: Mutations
Mutations changes in the DNA code due to:A. Point mutations: changes in the gene such as:
1. Substitution of one base to another - May have NO EFFECT on encoded protein 2. Insertion addition of an extra base in the code3. Deletion removal of a base from the sequence
*** #2 and #3 disastrous effect on resulting protein due to changes in reading frame
Point Mutation: Substitution
*** May have NO EFFECT on encoded protein!
Point Mutation: SubstitutionOR occasionally may cause detrimental effects sickle call anemia
Cont. MutationsB. Chromosomal Mutations: chromosome
rearrangements/ aberrations1. Deletion pieces of, or whole chromosome
missing2. Inversion piece of chromosome breaks off and
reattaches upside down3. Duplication extra piece of, or whole extra
chromosome4. Translocation piece of chromosome breaks off
and reattaches to nonhomologous chromosome
Mutagenic Agents any substance/ factor which causes either gene (point) or chromosomal mutations
1. Ultraviolet rays2. Gamma rays uncontrolled doses 3. X-rays cause formation of ions4. Chemicals w/in a cell
• Ions may interfere with:a. Normal pairing of one base with anotherb. Causes 2 bases that ordinarily do not combine, to form a pair ex) thymine may pair with guanine
• How would this affect DNA in cell replication? In protein synthesis?
Operona. Operon a group of genes
that operate togetherb. Promoter RNA polymerase
binding sitec. Operator (O) a regulatory
region where repressor binds to
d. Repressor enzyme that binds to O region/ turns operon “off” by preventing the transcription of genes
e. Regulatory gene synthesizes repressors (action of this protein determines whether genes are turned on/ off)
lac operon- w/o presence of lactose
In the absence of lactose, repressor switches off the operon by binding to the operator.
lac operon- w/ presence of lactose
• Inducible operon- usually turned off but can be INDUCED when lactose interacts w/ repressor protein• Repressor releases itself from operator- transcription starts!• Inducer- inactivates repressor (lactose)
trp operon• REPRESSIBLE OPERON- usually on, but can be inhibited (repressed) when tryptophan (trp) binds to repressor- Repressor binds to operator- transcription stops!- Corepressor- small mol (trp) that cooperates w/ repressor to switch off operon