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Chapter 17 Bio Study Guide Cheat Sheet by

-biology

Gene to Protein

inherited DNA leads to specific traits by dictating the synthesis of proteins

From Gene to Protein (cont.)

Gene expres­sion
process by which DNA directs protein synthesis (2 stages)
Trans­cri­ption
the synthesis of RNA using a DNA template
Trans­lation
the synthesis of a polype­ptide using the genetic inform­ation encoded in mRNA. (nucle­otides to amino acids)

Achibald Garrod

inborn errors of metabo­lism
inherited diseases when a person can't make a specific enzyme (no gene for enzyme bc of mutation)
ex.
alkapt­onura
 
pee is black because no enzyme exists to break down alkapton

Beadle and Tatum

one gene-one polype­ptide hypoth­esis
gene dictates the specific production of an enzyme
 
(gene codes for a polype­ptide aka protein aka enzyme)

DNA vs. RNA

 
DNA
RNA
strands
double and anti-p­arallel
single
3 part of nucleo­tides: 5-C sugar:
deoxyr­ibose
ribose
phosphate group:
present
present
nitrog­enous base
C, G, A, T
C, G, A, U

3 Types of RNA

mRNA
synthe­sized using DNA template, attaches to ribosome in cytoplasm and specifies the primary structure of protein
rRNA
molecu­les...and proteins make up the ribos­omes
tRNA
translates between nucleic acid (DNA) and protein lang. by carrying specific amino acids to ribosome, where they recognize the approp­riate codons in the mRNA
PROTEINS ARE ASSEMBLED ON RIBOSOMES
 

TRANSC­RIPTION is DNA-di­rected synthesis of RNA

eukaryotes
nucleus (where DNA is)
prokar­yotes
cytop­lasm
RNA polymerase II
binds to DNA and separates DNA strands
 
pastes compli­mentary RNA nucleo­tides to one side of DNA strand
 
= messenger RNA
RNA polymerase DOES NOT need a primer

Transc­ription (cont.)

prom­oter
DNA sequence where RNA polymerase II starts transc­ribing
term­ina­tor
DNA sequence where RNA polymerase II stops transc­ribing
tran­scr­iption unit
the entire stretch of DNA transc­ribed in mRNA

3 Stages of Transc­rip­tion:

init­iat­ion
after RNA polymerase binds to the promo­ter, the DNA unwinds and initiates RNA synthesis
 
proka­ryotes do this themse­lves
 
eukar­yotes use proteins called tran­scr­iption factors to assist bind of RNA polymerase to strand
 
TATA box helps position mRNA polymerase
Elon­gat­ion
RNA polymerase moves downst­ream, unwinding and elongating
Term­ina­tion
polymerase transc­ribes a sequence in DNA signaling end, RNA transcript is released, polymerase detaches from DNA

Modifying mRNA after Transc­ription

ends of pre-mRNA molecule are modified before leaving the nucleus
GTP cap
5' end receives guanine tripho­sphate cap
poly-A tail
3' end gets adenine nucleo­tides
RNA is made of :
exons (expresses code) and introns from DNA
 
INTRONS are cut out, while EXONS are spliced together by RNA splicing
RNA splicing signals are at both ends of an INTRON
protein spli­ceo­some snips out intron from transcript
 
enzyme of protein = ribo­zymes
 

Genetic Code

DNA and RNA
polymers of nucle­otides
nucleo­tides differ in bases
A,T,C,G vs. A,U,C,G
Genetic code
'language' of mRNA instru­ctions
codon
mRNA, 3-letter word
 
3 nucleotide that code for an amino acid
UCG =
amino acid methi­onine
prot­eins
amino acids join in polype­ptide
ALL proteins have a start (AUG) and terminator codon

Transl­ation

prokar­yotes & eukaryotes
cytoplasm on the ribosome
mRNA
left nucleus, now in cytoplasm, binds to ribosome
rRNA
ribosome composed of rRNA and protein; adds amino acids to polype­ptide chain
- 3 binding sites:
A site: holds the tRNA that carries the next amino acid
 
P site: holds the tRNA that carries the growing polype­ptide chain
 
E site: exit site for tRNA
tRNA
transfers amino acids to ribosome
 
other end of tRNA has anti­-co­don
- reference drawing for explan­ation -

_

poly­rib­oso­mes
mRNA can be translated simult­ane­ously by several ribosomes
transc­ription / transl­ation of BACTERIA cells occurs at same time because they're both in the CYTOPLASM

Mutations

alteration in the genetic inform­ation of a cell
point mutation - affects one nucleotide pair
nucl­eot­ide­-pair substi­tut­ion - replac­ement of one nucleotide and it's comple­mentary base pair in DNA
1. silent mutati­ons do not change amino acid transl­ation
2. missense mutation substi­tution when a codon still codes for an amino acid
3. nonsense mutati­ons - substi­tutions when a regular amino acid codon is changed into a stop codon, ending transl­ation

Mutations (cont.)

inse­rtion and deletion - addition / loss of nucleotide pairs, can cause frame­shift, mRNA read wrong
muta­gens - forces that interact with DNA in ways that cause mutation
ex. x-rays
REMEMBER:
- most genes only contain instru­ctions for assembling proteins
- many proteins = enzyme
- can control color of a flower

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