Module 9 : Study Guide

DNA (deoxyribonucleic acid)

double-stranded, made of nucleotides (sugar: deoxyribose, phosphate group, nitrogenous base: A, T, C, G)

RNA (ribonucleic acid)

single-stranded, sugar is ribose, bases are A, U C, G (U = uracil replaces T)

DNA pairs

A (adenine) pairs with T (thymine)

C (cytosine) pairs with G (guanine)

RNA pairs

A pairs with U (Uracil)

C pairs with G

what is the double helix and its discovery?

• DNA is a twisted ladder (double helix)

• discovered by james watson and francis crick

• strands are antiparallel (run in opposite directions : 5’ to 3’ and 3’ to 5’)

• held together by hydrogen bonds between bases

DNA replication (semi-conservative)

each new DNA molecule has one old strand + one new strand

helicase

unzip DNA

primase

lays down RNA primer

DNA polymerase

adds new nucleotides

ligase

joins DNA fragments (especially on the lagging strand)

gene

a section of DNA that codes for a protein

genotype

two alleles an individual has for a specific trait

phenotype

trait is expressed in the individual; appearance on the outside

transcription (DNA → mRNA)

• occurs in the nucleus

• DNA is used as a template to make mRNA

RNA polymerase

builds mRNA strand from DNA

promoter

start site for transcription

post-transcriptional modification

happens in eukaryotic cells (5’ cap added, poly-a tail added)

splicing

introns removed, exons joined

intron

non-coding region (removed)

exon

coding region (kept)

codon

3 mRNA bases = 1 amino acid

anticodon

3 tRNA bases that match the codon

start codon

AUG (codes for mathionine)

stop codons

UAA, UAG, UGA

structure of a ribosome:

ribosomal RNA (rRNA) and proteins

two subunits for ribosomes:

• large subunit (60 in euk, 50 in prok)

• small subunit (40 in euk, 30 in prok)

A site (aminoacyl)

accepts incoming tRNA with amino acid

P site (peptidyl)

holds tRNA with growing polypeptide chain

E site (exit)

releases empty tRNA

mRNA

carries genetic code from DNA

tRNA

brings amino acids to ribosome

ribosome

reads the mRNA and builds the protein

initiation

small ribosomal subunit binds to mRNA. start codon (AUG) is recognized. first tRNA (carrying methionine) binds

elongation

ribosome moves along mRNA, tRNAs bring amino acids, and peptide bonds form

termination

stop codon (UAA, UAG, or UGA) is reached. ribosome releases the completed polypeptide

where is the post-translational protein modifications?

golgi apparatus or endoplasmic reticulum (ER)

how does the post-translational protein modification?

folding, cleaving, adding chemical groups (phosphate, sugar, lipids)

mutation

a change in the DNA sequence that can affect protein production

point mutation

one base is substituted

frameshift mutation

base is inserted or deleted. shifting the reading frame

silent mutation

no change in amino acid

missense mutation

changes one amino acid

nonsense mutation

changes a codon to a stop codon

spontaneous

errors in DNA replication

induced of mutations:

radiation, chemicals, viruses

mutation in sickle cell anemia type:

missense point mutation

DNA change in sickle cell anemia:

GAG → GTG

mRNA codon in sickle cell anemia:

GAG → GUG

amino acid change in sickle cell anemia:

glutamic acid → valine

how the mutation affects hemoglobin?

clump together, distorted red blood cells (sickle shape), block blood flow and reduced oxygen delivery