DNA stores
genetic material
______ encodes the information to make polypeptides and RNA molecules
DNA (1)
________ is packaged in chromosomes and stored in the __________
DNA; nucleus
DNA ------> mRNA
transcription
mRNA------>protein
translation
The 5 levels of organization in DNA structure are
nucleotides, 2. single strand, 3. double helix, 4. chromosome, 5. genome
Chromosomes are composed of
chromatin
chromatin
DNA wound around histone proteins
Humans have how many chromosomes?
46 (23 pairs)
DNA nucleotide
phosphate group, sugar (deoxyribose), base
What are the bases of DNA?
Adenine, Thymine, Guanine, Cytosine
RNA nucleotides
phosphate group, sugar (ribose), base
What are the RNA bases?
Adenine, Uracil, Cytosine, Guanine
Nucleotide numbering system
Sugar carbons are 1' to 5' Hydroxyl group (-OH) attached to 3' carbon on sugar Phosphate attached to 5' carbon on sugar Base attached to 1' on carbon sugar
single strand
phosphodiester bonds link nucleotides forms sugar-phosphate backbone bases project away from backbone has directionality-5' to 3'
In a nucleotide single strand
sugars and phosphates alternate 5' has free phosphate group 3' has free sugar group
double helix
-double stranded helix -strands run antiparallel -bases project toward the center
complementary base pairing rules
A always pairs with T G always pairs with C
purines
Adenine and Guanine
Pyrimidines
Cytosine and Thymine
more characteristics of the double helix
-uses base pairing rules -antiparallel strands (3' to 5' with 5' to 3')
Chromosomes
consists of chromatin which is highly compacted DNA wrapped around histone proteins
To compact DNA and package into chromosomes:
double helix is wound into nucleosomes
nucleosomes to chromatin
30 nm fiber
radial loop domain
compacted radial loop domain
2 broad forms of chromatin
euchromatin (less compacted DNA, active genes) and heterochromatin (highly compacted DNA, inactive genes)
genome
all of an organism's genetic material
autosomal chromosomes
non-sex chromosomes 22 pairs in humans
sex chromosomes
Chromosomes that determine the sex of an individual 1 pair in humans
DNA replication
the process of making a copy of DNA for cell division
gamete production, cell renewal/growth, embryogenesis
DNA replication
DNA replication follows the __________ rule
AT/GC
during DNA replication
parental/original strands sperate and serve as template for the synthesis of a new/daughter strand
True or False: DNA replication is semi-conservative
True
Replication proceeds in _______ directions from an ________________________
both; origin of replication
origin of replication
Site where the replication of a DNA molecule begins.
replication fork
A Y-shaped region on a replicating DNA molecule where new strands are growing.
steps of the formation and movement of the replication fork
DNA helicase unwinds DNA at replication fork
Single-strand binding proteins bound to prevent reforming double helix
DNA topoisomerase prevents tangling of DNA ahead of replication fork
DNA polymerase links nucleotides together to form DNA strands
DNA polymerase
Enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule
DNA polymerase adds nucleotides to which prime end?
3'
A ______ primer is needed to start DNA replication
RNA
DNA primase
synthesizes short RNA primers
DNA replication process
On a strand 3' to 5':
RNA primer is laid down
leading strand of DNA is laid down to the replication fork From replication fork to origin (5' to 3')
RNA primer laid in front of origin of replication
Okazaki fragment is laid down from end to origin
process repeats to create the lagging strand
leading strand
The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' to 3' direction toward replication fork
lagging strand
A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.
Okazaki fragments
Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand.
True or False: The RNA primer can stay in the lagging strand.
FALSE: it must be replaced with DNA nucleotide AKA DNA polymerase
DNA ligase
Seals gaps between Okazaki fragments
True or False: DNA replication is very accurate
True, DNA polymerase has a proofreading mechanism to check for errors.
To fill in the 3' ends of the DNA strands, ___________ must be attached to the ends
telomeres
Telomeres
Repeated DNA sequences at the ends of eukaryotic chromosomes. -prevent loss of genetic material -added by enzyme telomerase -as we grow, telomeres are shortened
Genome
the complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes
Proteome
the entire set of proteins expressed by a given cell or group of cells
Gene
segment of DNA that encodes a functional product -can encode polypeptides or functional RNA molecules
gene expression
DNA stores info in genes
Transcription of DNA to produce RNA copy of gene
mRNA, the copy of gene that will be used to make polypeptide
Translation produces polypeptide using mRNA
DNA to RNA to polypeptide
gene expression (transcription and translation)
Where does the gene expression processes take place?
Prokaryotic- cytosol and ribosomes Eukaryotic-takes place in nucleus and ribosomes (either free or ones attached on Rough ER)
Transcription
synthesis of an RNA molecule from a DNA template
mRNA is complementary to
template strand (NONCODING STRAND)
mRNA sequence is the same as
non-template strand (CODING STRAND)
structure of a gene
promoter, regulatory sequence, terminator, transcribed region
Briefly describe the promoter, regulatory sequence, terminator, and transcribed region of a gene
promoter-START of transcription; place where RNA polymerase binds regulatory sequence-transcription factors (regulatory proteins) bind and control the rate of transcription terminator-END of transcription transcribed region-contains info that specifies an amino acid sequence; MIDDLE of gene
What are the three stages of transcription?
initiation, elongation, termination
Transcription initiation
sigma factor recognizes promoter and recruits RNA polymerase; DNA is unwound to separate strands; sigma factor released and RNA polymerase proceeds down DNA
Transcription Elongation
RNA polymerase continues down DNA strand using the template strand to make complementary RNA
Transcription Termination
When RNA polymerase reaches terminator, transcription stops & RNA chain is released
RNA processing in eukaryotes
-addition of 5' cap -addition of polyA tail -splicing AKA (Capping, Splicing, and tailing)
RNA splicing
Process by which the introns are removed from RNA transcripts and the remaining exons are joined together. (exons-expressed regions) (introns-intervening regions) -alternative splicing allows different proteins to be produced from the same gene
Organization of mRNA
ribosomal binding site-ribosome binding site, start codon-first amino acid, coding sequence-interchanging codons, stop codon-specifies stop
Codons
The three-base sequence of nucleotides in mRNA that specify a particular amino acid
The ______________ specifies amino acids within polypeptide
genetic code
The genetic code is _________________.
degenerate (same amino acid can be used repetitively)
tRNA contains what type of codon?
anticodon
Anticodon
group of three bases on a tRNA molecule that are complementary to an mRNA codon -carries amino acid specified by codon (tRNA)
AUG
start codon
UGA, UAA, UAG
stop codons
Where does translation occur?
ribosome
Characteristics of ribosomes
two subunits- Large and Small subunits composed of rRNA and proteins 3 sites where tRNA binds during translation: A, P, and E sites
________________ alter DNA sequence of a gene
Gene Mutation
Mutation
A change in a gene or chromosome. -heritable change -source of variation for natural selection -most are harmful -genetically inherited diseases result from harmful mutations
point mutation
gene mutation in which a single base pair in DNA has been changed -caused by base substitution
Three types of point mutations
silent, missense, nonsense
silent mutation
A mutation that changes a single nucleotide, but does not change the amino acid created. -causes no change in protein structure or function
missense mutation
A base-pair substitution that results in a codon that codes for a different amino acid. -may change protein structure/function or may not -usually neutral or negative outcome
nonsense mutation
A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein. -usually negative outcome
indel mutation (base insertion or deletion)
a mutation in which one or more nucleotide pairs is added or deleted -may cause change in reading frame -addition or deletion shifts the reading frame and changes codons and resulting amino acids
frameshift mutation
mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide -changes amino acid sequence -negative outcome; changes protein structure/function
mutations can also occur in _______________ regions
regulatory; may alter gene expression
Mutations occur in these type of cells:
germline and somatic
germline mutation
DNA alteration occurring in gametes that can be transmitted to offspring
somatic cell mutation
change within cells of the body, cannot be transmitted
spontaneous mutations
random change in the DNA due to errors in replication that occur without known cause
induced mutations
caused by environmental agents -chemical agents (cigarrete smoke or asbestos) -physical agents (UV light or X rays)
Cancer
caused by accumulation of mutations that eventually cause excessive cell proliferation (rapid cell division) -around 7-10 mutations
progression of cancer
initial tumor cells- accumulate mutations that increase cell division
benign tumor-overgrowth of normal cells 3.malignant tumor-overgrowth of abnormal (cancerous) cells 4.metastasis-malignat cells enter bloodstream or lymphatics and spread throughout the body
Mutations in these cells promote cancer
proto-oncogenes and tumor suppressor cells
Apoptosis
programmed cell death
Proto-oncogenes
promote normal cell division and growth -become oncogenes when develop gain-of-function mutation
Oncogenes
overactive, abnormal genes that promote excessive cell division and prevent apoptosis
Normal signaling pathway that promotes cell division
growth factor signal binds to a receptor, leading to receptor activation
signal transduction pathway
proteins/transcription factors are activated that promote transcription of genes involved in cell division ONCOGENES AFFECT ANY OF THESE AREAS
tumor suppressor genes
genes who's loss of activity promotes excessive cell division -encode proteins that normally prevent cell division, promote apoptosis, and involved in DNA repair
p53
tumor suppressor gene mutated in 50% of cancers -if DNA is damaged, p53 prevents cell division -if DNA is repaired, p53 cell divides normally -if DNA is not repaired, p53 promotes apoptosis