Unit 5: DNA and Protein Synthesis DNA- deoxyribonucleic acid *stores and transmits genetic information from one generation to the next -DNA is very large *there is about 9 feet of DNA in the nucleus of each of your cells

-DNA is composed of smaller units called nucleotides nucleotides- building blocks (monomers) of DNA Each nucleotides consists of: *5-carbon sugar (deoxyribose) *phosphate group *nitrogenous base

*two groups/four types Pyrimidines cytosine(C) and thymine(T) Nitrogenous Bases *two groups/four types Pyrimidines cytosine(C) and thymine(T) *contain one ring in their structure Purines adenine(A) and guanine(G) *contain two rings in their structure

-DNA consists of two strands of nucleotides wound around each other like a twisted ladder -this is known as a double helix *discovered by Watson and Crick

-the nitrogenous bases from both strands of nucleotides join together to form double helix -this is called base pairing (Chargaff’s Rule) -in base pairing, A bonds with T, G bonds with C

Prokaryotes -DNA is located in the cytoplasm -single circular DNA molecule -referred to as the cell’s chromosome

Eukaryotes -have 1000 times the DNA as prokaryotes -DNA not found free in the cytoplasm -DNA found in nucleus (as chromosomes) -chromosome # varies by species ex: humans =46 sequoia tree = 22 fruit fly = 8

-DNA is a very long molecule -there is about 6-9ft of DNA in one nucleus of one cell -it must fold to fit into cell -eukaryotic cells have both DNA and protein -the two together form chromatin -in chromatin, DNA wraps around proteins called histones

-DNA wrapped around 8 histones is called a nucleosome -histones then coil upon themselves to make a fiber that supercoils into the chromosome structure -nucleosomes allow long lengths of DNA to fold into the tiny space

DNA Replication -copying of DNA -each strand of DNA has what it needs to reconstruct the other half by base pairing -the sites where separation and replication occur are called replication forks

-before a cell divides, it replicates its DNA -this ensures each cell will have a complete set of DNA During DNA replication: DNA separates into two strands two new complementary strands are produced using rules of base pairing each strand serves as a model/template for the new strand

-DNA replication is carried out by enzymes -the enzymes unzip a molecule of DNA -occurs when hydrogen bonds are broken between the base pairs -main enzyme is DNA polymerase *joins individual nucleotides to produce DNA molecule *proofreads each DNA strand to make sure the new strands are identical to the original

genes- coded DNA instructions that control the production of proteins within the cell -the first step in decoding genes is to copy DNA to RNA -RNA contains coded info for making proteins

RNA (ribonucleic acid) -consists of a long chain of nucleotides like DNA -5 carbon sugar – ribose -phosphate group -nitrogenous bases: *NO THYMINE (T) *instead is uracil *A pairs with U -is single-stranded unlike double-stranded DNA

Types of RNA mRNA- (messenger RNA) *copies DNA and delivers code/instructions from DNA in nucleus to the rest of the cell rRNA- (ribosomal RNA) *makes up ribosomes tRNA- (transfer RNA) *carries amino acid to the ribosome coded to build protein

Protein Synthesis Two steps needed for DNA to create a protein: 1. transcription 2. translation

Step One: Transcription- Making mRNA -requires RNA polymerase (an enzyme) -RNA polymerase binds to DNA at a promoter site and separates the DNA strands promoter- area that has specific base sequences -RNA polymerase uses one strand as a template from which nucleotides are made into a strand of RNA -this is mRNA

RNA Editing -RNA needs some editing before it is ready RNA Editing -RNA needs some editing before it is ready *DNA is made of introns- non-coding regions and exons- coding regions -both introns and exons are copied from DNA when RNA is formed -introns are then cut out and exons are spliced together to form final mRNA

cut spliced

-proteins are made by joining amino acids into long chains called polypeptides -each polypeptide contains a combo of any or all of the 20 amino acids -sequence of amino acids determined by group of 3 bases on mRNA = codon -sometimes several codons code for the same amino acid -64 codons possible ex: UCG CAC GGU

-there is one codon, AUG, that can either be methionine or serve as a “start” codon for protein synthesis -there are three stop codons that signify the end of a polypeptide

For what amino acid does the codon UGC code? cysteine For what amino acid does the codon CCU code? proline page 303

Step Two: Translation- Making Proteins -the cell uses info from mRNA to produce proteins -mRNA is read by the ribosome -the code “calls” for amino acids to create a protein -amino acids brought into place by tRNA

Mutations -changes in genetic material -mistakes made by cell in copying DNA Types of Mutations Gene Mutations -produce changes in a single gene Examples: point mutations- involve changes in one or a few nucleotides -include substitutions (one base is changed to another) and insertions and deletions (a base is inserted or removed from DNA sequence)

-substitutions affect usually no more than a single amino acid -insertions and deletions can be more dramatic because it shifts codons -these changes are called: frameshift mutations because they shift the reading frame of the genetic message and changes every amino acid that follows

Substitution, Insertion and Deletion

Chromosomal Mutations -involves changes in the number or structure of chromosomes Examples: deletion: loss of all or part of a chromosome duplication: produces extra copies of part of a chromosome inversion: reverse the direction of parts of a chromosome translocation: occur when part of one chromosome breaks off and attaches to another

Chromosomal Mutations