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MOLECULAR GENETICS Chapter 12

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Page 1: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

MOLECULAR GENETICS

Chapter 12

Page 2: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

THE STRUCTURE OF DNA AND

DNA REPLICATION

Page 3: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

DNA - DEOXYRIBONUCLEIC ACID

To understand genetics, scientists had to learn the chemical makeup of the gene.

Scientists discovered that genes are made of DNA

Scientists also found that DNA stores and transmits the genetic information from one generation of an organism to the next.

Scientists began studying DNA structure to find out how it carries info, decides traits, and replicates itself.

Page 4: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

DNA – THE STRUCTURE

DNA is a long molecule made up of units called nucleotides.

Each nucleotide contains a 5-carbon sugar, a phosphate group, and a nitrogen-containing base.

There are four kinds of bases in DNA: Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

Page 5: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

THE NUCLEOTIDES

Green = 5-C sugar

Peach = phosphate

Page 6: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

WATSON AND CRICK

Watson and Crick made a 3-D model of DNA.

Their model was a double helix, in which two strands are wound around each other.

A double helix is like a twisted ladder Sugar and phosphates make up the side of

the ladder Hydrogen bonds between the bases hold

the strands together (the rungs)

Page 7: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

DNA

Page 8: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

CHARGAFF’S RULE

Aka the “base pairing rule” Chargaff’s rule states that bonds only

form between certain base pairs

A always pairs with T G always pairs with C

You must memorize this!!!!

Page 9: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

BASE-PAIRING

Page 10: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

WHERE CAN YOU FIND DNA?

Most prokaryotes have one large DNA molecule floating in the cytoplasm.

Eukaryotes have DNA in the nucleus. Amazing fact:

The nucleus of a human cell contains more than 1 meter of DNA!

Page 11: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

CHROMOSOMES

Contain both DNA and protein, which are tightly packed together to form chromatin.

Chromatin consists of DNA that is tightly coiled around proteins called histones.

This forms a beadlike structure called a nucleosome.

Nucleosomes pack with one another to form a thick fiber, which is shortened by a system of loops and coils.

Nucleosomes allow enormous amounts of DNA to fit into such a small region.

Page 12: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA
Page 13: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA
Page 14: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

DNA REPLICATION

Before a cell divides, it copies its DNA in a process called replication.

During replication: The DNA molecule separates into 2 strands

– each strand of the DNA molecule serves as a model for the new strand.

Following the rules for base pairing, new bases are added to each strand.

The end result is two identical strands.

Page 15: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

HOW DOES REPLICATION OCCUR?

Its carried out by a series of enzymes Some enzymes “unzip” the molecule of DNA –

the hydrogen bonds between bases are broken The two strands unwind and serve as templates

to create two new strands The key enzyme is called DNA polymerase –

joins individual nucleotides to produce a DNA molecule DNA polymerase is also involved in “proofreading”

each of the new DNA strands to minimize errors.

Page 16: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

DNA REPLICATION

Page 17: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

LET’S REPLICATE!

Original Strand = T A C G T TNew Strand =

Original Strand = ATCGGCAATCACGATNew Stand =

ATG CAA

TAGCCGTTAGTGCTA

Page 18: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

RNA AND PROTEIN SYNTHESIS

Page 19: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

“THE PROTEIN SYNTHESIS FAIRYTALE”

Once upon a time in a land far, far away, there lived a beautiful but greedy queen named Queen Alicia. The Queen was good to the people who lived in her kingdom but she had something, something of great value to her and she would not share it with anyone. She had locked up in the tower of the nucleus a magical cookbook and this cookbook was filled with amazing recipes. The village was a happy one except for one problem. All they had to eat was mutton (mushy, fatty meat). One day a man named mRNA found out that the Queen was hiding the magic cookbook and he wanted to know the recipes. He found a way in through a hole called a nuclear pore. He crawled up to the very highest tower and found the cookbook. He started to transcribe the information when Queen Jen entered the chamber.

Page 20: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

He ran out through another nuclear pore and ran through the fields of cytoplasm. He had a problem though. He could not cook, but he knew who could. He had heard of this amazing, very cool restaurant called the Ribosomal Café. The cook was notorious. He could even make mutton taste good. His name is rRNA. mRNA knew that RRNA was the man for the job. mRNA could do the recipes justice, but there was another problem. The cook only spoke French and mRNA only spoke English. So he had to find someone he could trust. He located the man named tRNA. tRNA was a translator, and could speak both English and French. He gave the recipes to tRNA and tRNA took them into the Ribosomal Café and gave them to chef rRNA who turned them into the most amazing food anyone in the village has ever eaten. After that you could always hear the chef singing “le poison, le poison, he he he, hu hu hu” and everyone lived happily ever after eating fish (protein).

Page 21: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

RNA – THE BASICS

For a gene to work, the genetic instructions in the DNA molecule must be decoded.

The first step is to copy the DNA sequence into RNA.

RNA is a molecule which contains instructions for making proteins.

Page 22: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

RNA – THE STRUCTURE

RNA is similar to DNA, except for: RNA contains the sugar ribose

DNA has deoxyribose RNA is single-stranded

DNA is double stranded RNA has uracil in place of thymine – A, U,

C, G DNA has A, T, C, G

Page 23: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA
Page 24: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

RNA MOLECULES – WHAT DO THEY DO? There are 3 kinds of RNA –

Messenger RNA (mRNA) What is this in the story? Has the instructions for joining amino acids to

protein Ribosomal RNA (rRNA)

What is this in the story? Assembles the proteins

Transfer RNA (tRNA) What is this in the story? Carries each amino acid to the ribosome

according to the coded message in mRNA Contains an anticodon to pair up with mRNA

Cookbook

Cook

Translator

Page 25: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA
Page 26: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

TRANSCRIPTION

Process of making (or copying) RNA from DNA Occurs in the nucleus During transcription:

DNA strands are separated RNA strand is built using one DNA strand as a

template DNA is transcribed (written) into RNA following

base-pairing rules except that U binds to A AU, TA

DNA Strand = TACGCTACGCCTAATACTNew mRNA Strand =

AUGCGAUGCGGAUUAUGA

Page 27: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

TRANSCRIPTION TO TRANSLATION

The directions for making proteins are in the order of the four nitrogenous bases

This code is read 3 letters at a time Each grouping of 3 letters is called a codon AUG/CGA/UGC/GGA/UUA/UGA

Each codon stands for one amino acid There is one “start” codon and 3 “stop”

codons Start = AUG Stop = UGA, UAA, UAG

Page 28: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

TRANSLATION

Process in which the cell uses info from mRNA to make proteins

Takes place in the ribosome How does it work?

mRNA moves into the cytoplasm and attaches to ribosome

As each codon of the mRNA moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA.

The ribosome joins together each amino acid and the protein chain grows.

When the ribosome reaches a stop codon, the polypeptide chain is released.

Page 29: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

HOW DO WE FIGURE OUT THE AMINO ACID?

Use a Codon Chart

Page 30: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA
Page 31: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

LET’S DO AN EXAMPLE!

1. DNA Strand = TACGCTACGCCTAATACT

2. mRNA Strand = AUGCGAUGCGGAUUAUGA

3. Split into codons = AUG/CGA/UGC/GGA/UUA/UGA

4. Create Protein =

Methionine -Arginine -Cysteine - Gylcine - Leucine

Page 32: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

MUTATIONS

Mutations are mistakes made when cells copy their own DNA.

Mutations are changes in the genetic material of a cell.

There are two types of mutations: Gene mutations – changes in a single gene Chromosomal mutations – change in the

number or structure of chromosomes and affect multiple genes

Page 33: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

GENE MUTATIONS

Point mutations (substitution)– Occur at a single point in the DNA

sequence Causes one base to replace another, which

only affects one amino acid Frameshift mutations (insertion,

deletion) – A base is added or removed All the codons are affected/changed

resulting in a completely different protein

Page 34: Chapter 12.  To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA

CHROMOSOME MUTATIONS

Change in structure of chromosomes Four types:

Deletions = ABC-DEF AC-DEF Duplications = ABC-DEF ABBC-DEF Inversions = ABC-DEF AED-CBF Translocations = ABC-DEF ABC-JKL

GH-IJKL GH-IDEF