Biology Unit 7

**Deoxyribonucleic Acid**

 DNA stands for, one of the two types of nucleic acids, The other is RNA,

DNA

store an organism’s genetic information, directs the synthesis of proteins, which in turn control traits,  is found in: The cell nucleus, Mitochondria, Chloroplasts (plants only), It is made up of repeating monomers, called nucleotides

Chromatin

un-condensed form of DNA,

Chromosomes

condensed form of DNA

Histones

coil into chromosomes the DNA must wrap around proteins

Nucleotide

repeating subunit of a nucleic acid, made up of three components: A **phosphate group,** A 5-carbon sugar (in DNA this sugar is **deoxyribose**), One of four **nitrogenous bases**: Adenine, Cytosine, Guanine, Thymine

Phosphate Group

chemical structure that consists of one phosphorus and four oxygen atoms

Deoxyribose

A 5-carbon sugar (in DNA this sugar)

Nitrogenous Bases

Adenine, Cytosine, Guanine, Thymine

Double Helix

these nucleotides come together in a repeating pattern, they create a twisted ladder shaped molecule

Rails of DNA Ladder

made up of repeating alternating units of deoxyribose and phosphate groups, held together by **covalent bonds**

Rungs of DNA ladder

base pairs, two complementary nitrogenous bases held together by **hydrogen bonds**

Base Pairs Rule

limits which nitrogenous bases can bond: Adenine bonds with thymine, Cytosine bonds with guanine

Adenine and Guanine

Purines

Thymine and Cytosine

Pyrimidines

Chargaff’s rule

DNA from the cell of any organism should have a 1:1 ratio of purine and pyrimidine bases.  Or more simply: %A=%T, %G=%C

Genes

Segments of DNA that code for a protein, be short or very long, depending on how many nucleotides are contained in their length, Humans have \~20,000, code for proteins, which control traits

DNA versus RNA

**DNA:** Codes genetic info, sugar is Deoxyribose, # of strands 2, bases: Adenine, Thymine, Cytosine, Guanine, Nucleus (Mitochondria, Chloroplasts), Interacts with RNA to create proteins

**RNA:** Codes for proteins, sugar is Ribose, # of strands 1, bases: Adenine, Uracil\*\*, Cytosine, Guanine \*\*Uracil is a pyrimidine, Nucleus, Cytoplasm, Rough ER, 3 types: Messenger RNA, Transfer RNA, Ribosomal RNA

DNA Replication

double-stranded molecule must split apart so that each strand can be copied, There are approximately 3 billion base pairs in the human genome and all of them must be copied before a cell divides

Semiconservative

each new strand contains one parent strand and one new, complementary strand

Replication Bubbles

the sites along a strand of DNA where the two halves have been split apart so each half of the strand can be copied

**5’ to 3’ Direction**

This means nucleotides can __only__ be added to the **3’** end

DNA Helicase

unwinds and unzips the double helix

DNA Polymerase

adds on nucleotides to the new strand

DNA Ligase

joins fragments of the new strand together

Mutation

any change in the original sequence of base pairs

Point Mutations

a change in a single nucleotide base, There are several types: Substitution, Insertion, and Deletion

Substitution

one letter replaces another in the sequence, Ex: A → G

Insertion

one base is added into the sequence, Ex: a new T is added in the middle of sequence

Deletion

one base is removed from the sequence, Ex: a C is removed

**DNA → mRNA → protein**

To control traits, proteins are made

**Transcription**

Happens before translation, first part of protein synthesis, occurs in the nucleus of eukaryotes, in the cytoplasm of prokaryotes

**Translation**

happens after Transcription, second part of protein synthesis, occurs at a ribosome in the cytoplasm

Messenger RNA

During transcription, DNA is unwound and unzipped, It is used as a template to create a strand, In eukaryotes, this occurs in the nucleus, In prokaryotes, this occurs in the cytoplasm

Codon

three base sequence that codes for a particular amino acid,

Anticodon

tRNA molecules have _________ which is complementary to the **codon** of the mRNA

mRNA

arrives at the ribosome, it gives the code for a protein, codon by codon

tRNA

molecules will bring the correct amino acid to the ribosome