Molecular genetics: DNA, RNA, and protein synthesis Chapter 12

What are nucleotides? Subunits of nucleic acids… They are made of 3 parts: 5-carbon sugar, phosphate group, and a nitrogenous base There are two types of nucleic acids: DNA RNA

DNA – What is it? Deoxyribonucleic Acid Long, double-stranded chain of nucleotides Contains genetic code Instructions for making the proteins that control cell function and physical traits of an organism.

Structure of DNA Physical Double helix (twisted ladder) Tightly coiled DNA + histones (proteins) = chromatin Before cell division, chromatin coils more tightly into chromosomes

More DNA Structure Chemical 5-carbon sugar (deoxyribose) Phosphate group Nitrogen base The “rails” are made of alter- nating deoxyribose and phosphate Groups.

What’s a Nitrogen Base? Introducing the nitrogen bases of DNA~~~ The part of a nucleotide that bonds with a partner to make up the “rungs of the ladder” in a double helix Introducing the nitrogen bases of DNA~~~ Adenine (A) Thymine (T) Cytosine (C) Guanine (G) A – T always pair and C – G always pair – these are the rungs of the ladder

What is the job of DNA? Stores all the information, “genetic code” The code is used to make proteins, which control almost everything that happens in your body A gene is a specific sequence of DNA that codes for a specific protein Replication – when the strands of DNA unwind and an exact copy of the entire length of DNA forms during cell division. This is important so that the new cell has the exact same info as the other cell.

Where in the cell is your DNA? Nucleus DNA is the master plan for a cell, and the cell wants to keep it safe. So the DNA stays inside the nucleus of the cell

DNA Structure and Function https://www.youtube.com/watch?v=_POdWsi i7AI

replication What does semiconservative replication mean? Parent strands of DNA separate and serve as templates to produce DNA molecules that have one strand of parental DNA and one strand of new DNA When does DNA replicate? Interphase What are the 3 main stages of replication? Unwinding and unzipping the 2 strands Base pairing – matched nucleotides are added to form new strand Joining – protein joins all the pieces that have been replicated

DNA Replication https://www.youtube.com/watch?v=5qSrmei Wsuc

RNA (DNA’s distant cousin) What is it? Ribonucleic Acid Long chain of nucleotides, with 5- carbon sugar, phosphate group, and nitrogen base (similar to DNA) Since the all-important DNA has to stay safely tucked away in the nucleus, we need RNA to make a copy of the code to travel to other parts of the cell, where the action happens…

What is the Central dogma? DNA codes for RNA, which guides the synthesis of proteins

What’s the difference? How is RNA different than DNA??? 5-carbon sugar is Ribose (instead of Deoxyribose) Nitrogen base Uracil (instead of Thymine). The others (Adenine, Cytosine, and Guanine) are the same as DNA. A – U pair and C – G pair Single-stranded It does not stay in the nucleus.

There are 3 types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Long strands of RNA that are complementary to DNA travel from the nucleus to the ribosome to deliver the instructions for creating a protein Ribosomal RNA (rRNA) Becomes part of the structure of a ribosome- forms ribosomes Transfer RNA (tRNA) Transport amino acids to the ribosome to build proteins

Why RNA is just as cool as dna https://www.youtube.com/watch?v=0Elo- zX1k8M

Hey Hey Hey, RNA… What are you going to do today? I’m going to take that DNA code and turn it into a protein! How? First, I copy DNA’s code. (DNA -> RNA =Transcription) Then, I use that code to stick certain amino acids together. The string of amino acids is called a polypeptide, which forms a protein (RNA -> protein = Translation)

What is transcription? Synthesis of mRNA from DNA- DNA code is transferred to mRNA in the nucleus and then the mRNA can leave the nucleus through the cytoplasm, traveling to the ribosomes so that proteins can be synthesized.

Breaking the code! 20 amino acids are used to make proteins. RNA is read 3 bases at a time (codon) AUG = start UAA = stop UAG = stop UGA = stop

Protein Synthesis The process of “translating” the RNA code into a chain of amino acids that form a protein is called Translation The “code” is read and translated to make a protein. Where in the cell? Protein synthesis occurs on the ribosome.

Making proteins 1. DNA unwinds and a matching copy of mRNA forms (Transcription). 2. Messenger RNA carries the code from the nucleus into the cytoplasm to the ribosome (the site of protein synthesis) 3.The genetic code on the mRNA is read 3 letters at a time (codon). Each 3-letter code matches up with a specific amino acid (the building blocks of proteins) (Translation).

Making proteins (continued) Transfer RNA carries the amino acid to the specific codon on the mRNA. 5. The amino acids bond together to form a long chain called a polypeptide, which forms a protein.

What’s the point of all this? When you eat protein, it gets broken down in your digestive system, into amino acids. Your body uses those amino acids as building blocks to build the proteins you need! (you are what you eat…) Proteins control almost everything in a cell. Proteins define what the cell looks like, how it functions, how it grows, and how it passes the information on Ex. Enzyme action, transport, motion, protection, support, communication, and regulation

What is a mutation and how can it lead to a genetic disorder? A mutation is a mistake, or a permanent change in a cell’s DNA. It can be a gain or a loss of nucleotides, or just a switch from one nucleotide to another. It can lead to a genetic disorder because when the DNA is altered, it affects which amino acids combine to form a protein.

What are some causes of mutation? Mutagens, such as chemicals and radiation (x-rays, uv rays from sunlight)

What is the major difference in the effects of mutations in body cells compared to sex cells? Mistakes in the DNA of one body cell will only affect the cell (or daughter cells) until it dies. These are not passed on to the next generation. Damage to the DNA of a sex cell will get passed on to offspring and then affect every cell in the body.