Studied by 7 peopleDeoxyribonucleic Acid (DNA)
a double-stranded polymer of nucleotides (each consisting of a deoxyribose sugar, a phosphate, and four nitrogenous bases) that carries the genetic information of an organism.
Friedrich Miescher
he took pus cells from infections and found that the nuclei of cells contained a substance that did not act like protein - thought to be the heredity material
Joachim Hammerling
worked with green algae and observed that regeneration of new appendages was driven by the nucleus-containing foot. he hypothesized that hereditary information is stored in the nucleus.
Erwin Chargaff
discovered that in the DNA of numerous organisms the amount of adenine is equal to the amount of thymine, and the amount of guanine is equal to that of cytosine.
Alfred Hershey and Martha Chase
worked with viruses and bacteria. they put a radioactive marker on the virus DNA and a different one on the protein coat. they found that only the marked DNA entered the bacteria. this provided the final evidence that DNA was the heredity material.
Rosalind Franklin
using an x-ray, she discovered how wide DNA is.
James Watson and Francis Crick
by knowing what DNA was made of (deoxyribose sugar, phosphate group, and nitrogenous bases, discovered in the 1920s) and using the information from chargaff and franklin, they discovered the double-helix structure of DNA.
Walter Flemming
came up with the terms chromatid and chromosome when he saw them in cells. in greek, chromatid means colour and chromosome means colour body.
Appearance of a DNA Molecule
double helix (like a zipper) - twisted ladder, histones (proteins)
Three Components of a Nucleotide
nitrogenous base, phosphate group (PO₄)³⁻, and ribose sugar (5-carbon sugar)
Two Kinds of Nitrogenous Bases
purines and pyrimidines
Purine
adenine and guanine. double ring structure (larger).
Pyrimidine
cytosine and thymine. single ring structure (smaller).
Possible Base Pair Combinations
four possibilities: A-T, T-A, G-C, and C-G. A and T have two hydrogen bonds and G and C have three.
What makes up the genetic code?
the order of the nitrogenous bases
Main Information Stored in the Genetic Code
protein synthesis (need to know amino acids and its order). instructions for life, information on constructing proteins.
Why the DNA Molecule Coils
the 3' end and 5' end of the deoxyribose cause it to coil. nature of chemical bonds on the "ladder rails" make it coil (phosphate and sugar). convenient way to pack lots of genetic code into a small space.
DNA Diagram
DNA Helicase
the enzyme that uncoils DNA and unzips it. breaks the hydrogen bonds holding the two complementary parent strands together, resulting in an unzipped helix that terminates at the replication fork.
DNA Gyrase
the enzyme that holds the DNA as it is splitting so that it does not break or get tangled. relieves any tension from the unwinding of the double helix.
Single-Stranded Binding Protein (SSB)
a protein that keeps separated strands of DNA apart. anneals to the newly exposed template strands, preventing them from reannealing.
Replication Fork
location where the DNA is splitting
Replication Bubble
creation of two replication forks. creates better efficiency.
Primase
an enzyme that lays down RNA primers.
RNA Primers
a sequence of 10 to 60 RNA bases added to a section of single-stranded DNA to act as a starting point for DNA replication. used by DNA polymerase III as a starting point to build the new complementary strands.
DNA Polymerase III
adds complementary nucleotides in the 5' to 3' direction, using RNA primers as starting points (used in the lagging and leading strand). adds the appropriate deoxyribonucleoside triphosphates to the 3' end of the new strand using the template strand as a guide. the energy in the phosphate bonds is used to drive the process. (in the image, it copies from the 5 to the 3)
Leading Strand
the new strand of DNA that is made continuously during DNA replication. it is made towards where the DNA is splitting (replication fork).
Lagging Strand
the new strand of DNA that is made in short fragments (because DNA is made in a 5' to 3' direction of the new DNA strand). the fragments are later joined together. made away from the replication fork.
Okazaki Fragments
short pieces of DNA that are made on the lagging strand.
DNA Polymerase I
an enzyme that removes RNA primers and replaces them with the appropriate nucleotides
DNA Ligase
an enzyme that fills in the gaps between the DNA/okazaki fragments on the lagging strand by the creation of a phosphodiester bond.
What enzymes proof read DNA?
DNA polymerase I and III. they do so by cutting out incorrectly paired nucleotides at the end of the complementary strand and adding the correct nucleotides.
Protein Synthesis is the _______________________ of Biology
central dogma
Genes
a sequence of nucleotides in DNA that perform a specific function, such as coding for a particular protein. (gene -> protein). made up of a section of DNA/a bunch of nucleotides. the human body is estimated to have 3 billion genes with 42,000 being protein-encoding. there are thousands of genes on each chromosome.
Why can't DNA make protein directly?
DNA is too valuable to be allowed to exit the nucleus. it could get damaged which would result in the death of the cell or organism. there are only two copies in the nucleus, so very little protein could be made at once. once the protein is made, the DNA would have to reenter the nucleus for storage. the complications of reentry are endless.
Transcription
the copying of information in DNA into messenger RNA (mRNA). made up of four processes.
Four Processes of Transcription
initiation
elongation
termination
post-transcriptional modifications
Transcription Initiation
transcription begins when RNA polymerase attaches to DNA at a promoter region. the promoter region shows where the gene starts, characterized by a lot of A and T base pairs (TATA box). a section of DNA is unwound.
Transcription Elongation
RNA polymerase begins making mRNA. only one strand of the DNA is used, it is called the template strand, the other stand is known as the coding strand. the RNA sequence is complementary to the template strand and identical to the coding strand, except that it contains uracil instead of thymine. made in the 5' to 3' direction.
Transcription Termination
the mRNA strand is made until the end of the gene is reached. the end is indicated by a terminator sequence (ATC). the mRNA separates from the DNA, the RNA polymerase falls off, and the DNA reforms its double-helix.
Transcription Post-Transcriptional Modifications
some things need to be done to the mRNA before it leaves the nucleus. a 5' cap is added to the start of the mRNA, this will protect it from digestion in the cytoplasm and aid with binding to the ribosome. a poly-A tail is added to the 3' end. the last step is to remove the introns from the mRNA so the protein can fold properly. spliceosomes remove the introns and join the remaining exons.
Exon
sections in DNA that code for part of a protein
Intron
sections in DNA that do not code for part of a protein. 95% of the human genome is noncoding.
Translation
involves a ribosome using the mRNA to make a protein out of amino acids. made up of three processes. occurs in the cytoplasm.
Three Processes of Translation
initiation
elongation
termination
Translation Initiation
the ribosome (actually made up of a large and small subunit) binds to the 5' cap of the mRNA. the ribosome moves along the mRNA, reading the code in triplets known as codons. translation does not begin until the start codon is read (AUG).
Translation Elongation
the ribosome has two binding sites, the P (peptide) site and the A (acceptor) site. when the start codon is in the P site, a tRNA delivers the corresponding amino acid. tRNA recognizes the codon because of the complementary anticodon, every tRNA carries only one specific amino acid. the second codon is now at site A. a second tRNA delivers the next appropriate amino acid to site A and a peptide bond is formed between it and the first amino acid. the ribosome shifts over one codon and the tRNA that brought the first amino acid leaves. the second tRNA shifts over to the P site and a third tRNA moves into the A site.
Translation Termination
the process of elongation continues until a stop codon (UAG, UGA and UAA) is read in site A. a protein, known as the release factor, recognizes the ribosome has stopped and causes the subunits to fall off, releasing the mRNA and the newly formed protein. the protein is folded and sent to where it is needed.
Mutations
changes in the DNA sequence that are inherited. we have two copies of each gene. one from mom and one from dad. if there is an error in one, the other copy will compensate. our genes have lots of mutations. if we only had one copy, much of the population would not be alive.
Three Types of Mutations
silent mutations, point mutations, and chromosome mutations.
Silent Mutations
has no effect on the operation of the cell. often occurs in the introns of DNA and they get cut out during transcription.
Point Mutations
mutations that are specific to one base pair. three types: substitution, deletion, and insertion.
Substitution
the replacement of one base pair by another in a DNA sequence. it could make the codon code for another amino acid or result in a stop codon in the middle of making a protein.
Deletion
the elimination of a base pair. it could result in drastic error because all the codons have been shifted over one.
Insertion
the placement of an extra nucleotide in a DNA sequence. has the same consequences as a deletion: drastic error because all the codons have been shifted over one.
Chromosome Mutations
mutations that involve a section of DNA. two types: translocation and inversion.
Translocation
the transfer of a fragment of DNA from one chromosome to another. the transfer is between nonhomologous chromosomes. when the cell is making a protein, part way through it reads the instructions for another protein. occurs in some types of leukemia.
Inversion
the reversal of a segment of DNA within a chromosome.
Two Causes of Mutations
spontaneous mutations and induced mutations
Spontaneous Mutations
mutations as a result of errors made in DNA replication. DNA polymerase rereads the DNA and sometimes it misses mistakes.
Induced Mutations
mutations caused by a chemical agent or radiation. UV light contains enough energy to cause a point mutation, which could result in skin cancer. x-rays have the ability to break DNA, enzymes will repair it but in the process, some base pairs may be lost. cancer is a mutation in the genetic sequence of genes that control cell growth and division. cystic fibrosis is often a 3-base-pair deletion. numerous pesticides have been linked to deletion mutations.
Prokaryote Genome
small and circular. all regions are coding, except for promoters and operators.
Eukaryote Genome
large and arranged in chromosomes. consists of coding and noncoding regions.
Prokaryote Transcription
coupled with translation. lack of introns means no excision.
Eukaryote Transcription
occurs in the nucleus. introns excised by spliceosomes and exons joined together.
Prokaryote Translation
commences with formyl-methionine. ribosome recognizes shine-dalgarno sequence on mRNA as binding site. ribosomes are smaller than in eukaryotes.
Eukaryote Translation
commences with methionine. ribosome recognizes 5' cap on mRNA as binding site. occurs in the cytoplasm. ribosomes are larger than in prokaryotes.
CRISPR
used for accurately removing and altering a specific part of DNA.
Gel Electrophoresis
a laboratory method used to separate large quantities of DNA and RNA according to their size and length.
Plasmids
generally, it's used to manipulate gene expression in the target cells. they are genetically modified to produce one or two specific proteins from a pathogen and purified to be used for immunization.
Polymerase Chain Reaction
a method that is used widely to make millions to billions of copies of DNA.
DNA Sequencing
the process in which the nucleic acid sequence (order of nucleotides in DNA) is determined in various organisms.
Old vs. New DNA
old is the template that makes the new
DNA vs. RNA
DNA: deoxyribose sugar, thymine, double helix, longer, two copies, in the nucleus, one type. RNA: ribose sugar, uracil, single helix, shorter, tons of copies, in the nucleus and cytoplasm, three types (mRNA, tRNA, rRNA)
mRNA
messenger RNA: carries information from DNA blueprint to site of protein synthesis
tRNA
transfer RNA: transfers information into amino acid language
rRNA
ribosomal RNA: controls manufacturing process
Does mRNA copy the whole DNA molecule?
no, the whole molecule codes for every single thing. it only copies the section/gene it needs at the time.
Basic Structure of the DNA Code
a codon - three nitrogenous bases. allows for 64 possible code combinations. each codon codes for one amino acid (or a stop codon, etc.)
Single-Stranded Binding Protein (SSB)
a protein that keeps separated strands of DNA apart. anneals to the newly exposed template strands, preventing them from reannealing.
Note
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