Download DNA and Protein Synthesis

DNA and Protein Synthesis
CHAPTER 10
Biology and Society:
Mix-and-Match Viruses


In 2009, a cluster of unusual flu cases broke out around
Mexico City.
In June 2009, the World Health Organization (WHO)
declared H1N1 a pandemic (global epidemic) and
 unveiled a massive effort to contain it.


Scientists soon determined that H1N1 was a hybrid flu strain,
made when a known flu virus mixed with an Asian swine flu
virus.



The hybrid H1N1 flu strain had a combination of genes that
infected young, healthy people instead of the elderly or people
who were already sick.
Many countries produced a coordinated response, and the
WHO declared the pandemic over in August 2010.
What are genes made of?
DNA




was known to be a chemical in cells by the end of the nineteenth
century,
has the capacity to store genetic information, and
can be copied and passed from generation to generation.
The discovery of DNA as the hereditary material ushered in the
new field of molecular biology, the study of heredity at the
molecular level.
I. DNA & the genetic code
A. Definitions
1. Gene
a. segment of DNA
b. codes for a certain
trait (protein)
c. Ie. Hair color gene
causes cell to make brown hair
B. Structure of DNA
deoxyribonucleic acid
1. STRUCTURE DISCOVERED BY
WATSON AND CRICK
2. Many nucleotides joined together
a. What is a nucleotide
Three part molecule
a-deoxyribose sugar
a- phosphate
a-nitrogen base
3. SHAPED INTO A DOUBLE HELIX
(SPIRAL)
-- LOOKS LIKE A TWISTED LADDER
4.
5.
NITROGEN BASES MAKE UP THE STEPS
OF THE LADDER
10 - 1,000 STEPS FOR ONE GENE
6. Four nitrogen bases make up the steps
- adenine A-double ring structure
- thymine T-single ring structure
- guanine G-double ring structure
- cytosine C-single ring structure
7. Bases always match with its compliment
A—T
G—C
II. Two functions of DNA
 1. replication
 2. protein synthesis
REPLICATION- in cell nucleus
 Purpose: when cells or organisms reproduce, a
complete set of genetic instructions passes to next
generation-DNA doubles
1. Hydrogen bonds b/w nitrogen bases break
2. DNA unzips
3. New nucleotides come in & join w/complimentary
bases
- uses enzyme DNA polymerase
4. 2 identical strands of DNA are present
DNA Replication
DNA replication cont.
 DNA replication ensures that all the body cells in multicellular
organisms carry the same genetic information.
 DNA can be damaged by X-rays and ultraviolet light.

DNA replication in eukaryotes
begins at specific sites on a double helix (called origins of
replication) and
 proceeds in both directions.

Origin of
replication
Parent
strand
bubble
Parent
strands
Daughter
strand
THE FLOW OF GENETIC INFORMATION FROM
DNA TO RNA TO PROTEIN

DNA provides instructions to
a cell and
 an organism as a whole.

How an Organism’s Genotype Determines Its
Phenotype


An organism’s genotype is its genetic makeup, the sequence of
nucleotide bases in DNA.
The phenotype is the organism’s physical traits, which arise
from the actions of a wide variety of proteins.
How an Organism’s Genotype Determines Its Phenotype

DNA specifies the synthesis of proteins in two stages:
1.
2.
transcription, the transfer of genetic information from DNA
into an RNA molecule and
translation, the transfer of information from RNA into a
protein.
transcription
DNA
transcription
RNA
nucleus
cytoplasm
translation
protein
Transcription: From DNA to RNA

Transcription
makes RNA from a DNA template,
 uses a process that resembles the synthesis of a DNA strand during
DNA replication, and
 substitutes uracil (U) for thymine (T).
 RNA nucleotides are linked by the transcription enzyme RNA
polymerase.

RNA polymerase
DNA- colors represent genes
RNA polymerase
RNA
nucleotides
RNA
DNA
template
RNA
Steps of transcription
1.
2.
3.
4.
5.
6.
DNA unzips by breaking hydrogen bonds
One strand is active, one is inactive
RNA nucleotides join to active strand
Controlled by RNA polymerase
mRNA is ready for processing
Original DNA strands rejoin
RNA processing

RNA processing includes
adding a cap and tail consisting of extra nucleotides at the ends of
the RNA transcript,-this protects RNA from cell enzymes
 removing introns (noncoding regions of the RNA), and
 RNA splicing, joining exons (the parts of the gene that are
expressed) together to form messenger RNA (mRNA).

DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed Tail
Exons spliced together
mRNA
Coding sequence
Nucleus
Cytoplasm
Translation
 Translation is the conversion from the nucleic acid language to
the protein language.
 Translation requires
mRNA,
 ATP,
 enzymes,
 ribosomes, and
 transfer RNA (tRNA).

How translation occurs
1. mRNA attaches to ribosome to be decoded
- code is read in pieces called codons
- codon – 3 nucleotides
AUG CCU GGA
- each codon codes for one amino acid
2.
A new kind of RNA brings in the correct amino
acid.
- transfer RNA (tRNA) see diagram
one end has the a.a. on it
the other end has an anticodon
 Anticodon 3 nucleotides on tRNA that base pair with
nucleotides on mRNA
- see diagram of tRNA
This is how the correct a.a. is brought in
Steps of translation
1. Correct tRNA (carrying it’s specific a.a.)base pairs
w/M-RNA (called initiation)
1st codon is always AUG (start codon)
2. Another tRNA base pairs w/the next codon (called
elongation)
3. Peptide bond is formed b/w the a.a’s
4.
1st tRNA releases it’s a.a and leaves
5.
mRNA moves over & process continues
Process continues until a stop codon is reachedthe stop codon signals termination (3rd step)
Protein is released –ribosome splits into its 2
subunits
6.
7.
mutations


Mutations can change the amino acids in a protein.
Mutations can involve
large regions of a chromosome or
 just a single nucleotide pair, as occurs in sickle-cell disease.


A mutation is any change in the nucleotide sequence of DNA.

Mutations within a gene can be divided into two general
categories:
1.
2.

nucleotide substitutions (the replacement of one base by
another) and
nucleotide deletions or insertions (the loss or addition of a
nucleotide).
Insertions and deletions can


change the reading frame of the genetic message and
lead to disastrous effects.
Single base substitution- sickle cell anemia
Deletions,insertions
Causes of mutations
What causes mutation?
1. Mutagen – substance that causes DNA to change
-- drugs, X-rays, UV rays
2. Unknown - during replication DNA can make a
mistake