PROTEIN SYNTHESIS. Or how our bodies make proteins!

Transcription

1 PROTEIN SYNTHESIS Or how our bodies make proteins!

2 What is the function of DNA The DNA molecule contains all your hereditary information in the form of genes A gene is a coded section of DNA; it tells our cells how to build specific proteins Genes code for EVERYTHING our body needs and does (saliva, bones, eye shape) Because DNA is so large, it is stuck inside the nucleus It needs a messenger to move the information from nucleus to protein production locations (ribosomes!)

3 What is the history of DNA Chromosomes are made of both DNA and protein DNA is made up of nucleotides, which consists of a nitrogen base, a pentose sugar, and a phosphate group. Proteins were composed of 20 different amino acids in long polypeptide chains 3

4 History of DNA Two strands coiled called a double helix Center made of nitrogen bases bonded together by weak hydrogen bonds 4

5 What is the rule for DNA Adenine must pair with Thymine Guanine must pair with Cytosine The bases form weak hydrogen bonds T A G C copyright cmassengale 5

6 What is RNA! RNA is a nucleic acid messenger between DNA and ribosomes 3 differences between DNA and RNA: RNA has ribose sugar RNA is single stranded RNA contains a nitrogen base called uracil (U) instead of thymine.

7 What is the rule for RNA Adenine must pair with Uracil Guanine must pair with Cytosine The bases form weak hydrogen bonds U A G C copyright cmassengale 7

8 DNA RNA - Double stranded molecule - Contains thymine - Contains deoxyribose sugar - Found only in nucleus - Made of nucleotides - Contain adenine, guanine, and cytosine - Single stranded molecule - Contains uracil - Contains ribose sugar - Found in nucleus and cytoplasm

9 Does this diagram represent DNA or RNA? how can you tell?

10 You are a

11 What are the 3 types of RNA Messenger RNA (mrna): copies DNA in the nucleus and carries the info to the ribosomes (in cytoplasm) Ribosomal RNA (rrna): makes up a large part of the ribosome; reads and decodes mrna Transfer RNA (trna): carries amino acids to the ribosome where they are joined to form proteins

12 What is Protein synthesis Protein synthesis is the assembly of amino acids (by RNA) into proteins Involves two steps: 1. Transcription copying DNA code into mrna 2. Translation reading the mrna code and assembling amino acids into a polypeptide chain (protein)

13 How transcription works 1. DNA strand splits, exposing the active strand 2. Complementary mrna nucleotides line up opposite the active strand, forming mrna 3. mrna leaves the nucleus Transcription demo

14 What is the Semiconservative Model of Replication Method of DNA replication in which parental strands separate, act as templates, & produce molecules of DNA with one parental DNA strand & one new DNA strand New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA DNA Template Parental DNA New DNA copyright cmassengale 14

15 Decoding mrna (translation) The sequence of bases in an mrna molecule serves as instructions for the order in which amino acids are joined to produce a polypeptide Ribosomes decode the instructions by using codons, sets of 3 bases that each code for 1 amino acid Each codon is matched to an anticodon, or complementary sequence on the trna to determine the order of the amino acids Translation demo

16 estion.png Using a codon chart A codon chart is used to determine the sequence of the amino acids in the polypeptide The sets of 3 mrna bases (codons) are used to find the amino acid

17 Decoding Practice For the following DNA examples, first give the appropriate mrna sequence, then identify the amino acid sequence (remember: U replaces T in mrna) Example 1: DNA: mrna: TAC GCA TGG AAT AUG CGU ACC UUA Amino Acids: Met Arg Thr Leu Example 2: DNA: mrna: CGT GGA GAT ATT GCA CCU CUA UAA Amino Acids: Ala Pro Leu stop Translation Review

18 DNA replication is very accurate DNA polymerase laying down new nucleotides makes1 error per 1,000,000 nucleotides Sounds good? 3,000,000,000 base pairs in the each human cell 3,000 possible errors each time our cells replicate BUT after DNA Polymerase is done, other enzymes proofread and correct the new strand Afterward, the error rate is about 1 error per 10,000,000,000 or 1 error every 3 cell divisions.

19 Replication practice T G C A G DNA A T polymeras DNA e polymerase T G C A G A T new new strands strands old old strands strands helicase A C G T C T A C G T C T

20 Environmental Influences In prokaryotes and eukaryotes, environmental factors like temperature, salinity, and nutrient availability can influence gene expression. For example, the lac operon in E. coli is switched on only when lactose is the only food source in the bacteria s environment.

21 Metamorphosis involves a series of transformations from one life stage to another, such as the transformation of a tadpole to an adult bullfrog. It is typically regulated by a number of external (environmental) and internal (hormonal) factors. Environmental Influences Metamorphosis is another example of how organisms can modify gene expression in response to their environment.

22 Environmental Influences As organisms move from larval to adult stages, their body cells differentiate to form new organs. At the same time, old organs are lost through cell death.

23 Environmental Influences For example, under less than ideal conditions a drying pond, a high density of predators, low amounts of food tadpoles may speed up their metamorphosis. The speed of metamorphosis is determined by various environmental changes that are translated into hormonal changes, with the hormones functioning at the molecular level.

24 What are Mutations Mutations are heritable changes in genetic information.

25 Types of Mutations All mutations fall into two basic categories: Those that produce changes in a single gene are known as gene mutations. Those that produce changes in whole chromosomes are known as chromosomal mutations.

26 Gene Mutations Mutations that involve changes in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence. They generally occur during replication. If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.

27 Gene Mutations Point mutations include substitutions, insertions, and deletions.

28 Substitutions In a substitution, one base is changed to a different base. Substitutions usually affect no more than a single amino acid, and sometimes they have no effect at all.

29 Substitutions In this example, the base cytosine is replaced by the base thymine, resulting in a change in the mrna codon from CGU (arginine) to CAU (histidine). However, a change in the last base of the codon, from CGU to CGA for example, would still specify the amino acid arginine.

30 Insertions and Deletions Insertions and deletions are point mutations in which one base is inserted or removed from the DNA sequence. If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings shift in every codon that follows the mutation.

31 Insertions and Deletions Insertions and deletions are also called frameshift mutations because they shift the reading frame of the genetic message. Frameshift mutations can change every amino acid that follows the point of the mutation and can alter a protein so much that it is unable to perform its normal functions.

32 What are Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of chromosomes. These mutations can change the location of genes on chromosomes and can even change the number of copies of some genes. There are four types of chromosomal mutations: deletion, duplication, inversion, and translocation.

33 What is deletion Deletion involves the loss of all or part of a chromosome.

34 What is duplication Duplication produces an extra copy of all or part of a chromosome.

35 What is inversion Inversion reverses the direction of parts of a chromosome.

36 What is translocation? Translocation occurs when part of one chromosome breaks off and attaches to another.

37 What are Mutagens Some mutations arise from mutagens, chemical or physical agents in the environment. Chemical mutagens include certain pesticides, a few natural plant alkaloids, tobacco smoke, and environmental pollutants. Physical mutagens include some forms of electromagnetic radiation, such as X-rays and ultraviolet light.

38 How do mutations affect genes? Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function. Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments.

39 Effects of Mutations Genetic material can be altered by natural events or by artificial means. The resulting mutations may or may not affect an organism. Some mutations that affect individual organisms can also affect a species or even an entire ecosystem.

40 Small changes in genes can gradually Effects of Mutations Many mutations are produced by errors in genetic processes. For example, some point mutations are caused by errors during DNA replication. The cellular machinery that replicates DNA inserts an incorrect base roughly once in every 10 million bases.

41 Effects of Mutations Stressful environmental conditions may cause some bacteria to increase mutation rates. This can actually be helpful to the organism, since mutations may sometimes give such bacteria new traits, such as the ability to consume a new food source or to resist a poison in the environment.

42 Mutagens If these mutagens interact with DNA, they can produce mutations at high rates. Some compounds interfere with basepairing, increasing the error rate of DNA replication. Others weaken the DNA strand, causing breaks and inversions that produce chromosomal mutations.

43 Harmful and Helpful Mutations The effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function. Whether a mutation is negative or beneficial depends on how its DNA changes relative to the organism s situation. Mutations are often thought of as negative because they disrupt the normal function of genes. However, without mutations, organisms cannot evolve, because mutations are the source of genetic variability in a species.

44 Harmful Effects Some of the most harmful mutations are those that dramatically change protein structure or gene activity. The defective proteins produced by these mutations can disrupt normal biological activities, and result in genetic disorders. Some cancers, for example, are the product of mutations that cause the uncontrolled growth of cells.

45 Harmful Effects Sickle cell disease is a disorder associated with changes in the shape of red blood cells. Normal red blood cells are round. Sickle cells appear long and pointed. Sickle cell disease is caused by a point mutation in one of the polypeptides found in hemoglobin, the blood s principal oxygencarrying protein. Among the symptoms of the disease are

46 Beneficial Effects Some of the variation produced by mutations can be highly advantageous to an organism or species. Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments. For example, mutations have helped many insects resist chemical pesticides.

47 Beneficial Effects Plant and animal breeders often make use of good mutations. For example, when a complete set of chromosomes fails to separate during meiosis, the gametes that result may produce triploid (3N) or tetraploid (4N) organisms. The condition in which an organism has extra sets of chromosomes is called polyploidy.

48 Beneficial Effects Polyploid plants are often larger and stronger than diploid plants. Important crop plants including bananas and limes have been produced this way. Polyploidy also occurs naturally in citrus plants, often through spontaneous mutations.