6Th Year Biology Higher Level Wesley Hammond DNA And

th 6 Year Biology Higher Level Wesley Hammond

DNA and RNA

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Contents:

Structure of DNA …………………………………………………………………………………………….3 Genetic Code …………………………………………………………………………………………………..4 DNA Replication ……………………………………………………………………………………………..5 DNA Profiling …………………………………………………………………………………………………6 Application of DNA Profiling …………………………………………………………………………...7 Genetic Screening …………………………………………………………………………………………..8 Detailed look at DNA ………………………………………………………………………………………9 RNA ……………………………………………………………………………………………………………..10 Protein Synthesis ………………………………………………………………………………………….12 Exam Questions ……………………………………………………………………………………………15

DNA and RNA can be worth 5% if asked as a short question in Section A.

DNA and RNA can be worth 7.5% if asked as an experiment in Section B.

DNA and RNA can be worth 15% if asked as a long question in Section C.

Note: DNA and RNA question has been asked every year since 2004 except for 2009.

2 ©The Dublin School of Grinds Wesley Hammond

DNA and RNA Structure of DNA

DNA = deoxribonucleic acid

 DNA is located inside the nucleus of a cell.  DNA can fit into a nucleus as it can coil and fold.  DNA has two strands.

NOTE: DNA is also found in the mitochondria and chloroplast of cells.

There are four bases used in DNA:

A = adenine T = thymine G = guanine C = cytosine

The four bases can only join (bond) with one other base:

Structure of DNA

3 ©The Dublin School of Grinds Wesley Hammond What shape does DNA have?

 DNA have a double helix shape

What is a gene?

 A gene is a section of DNA that causes the production of protein.

The Genetic code

How many amino acids are used in the production of proteins? 20

A gene carries different codes to control the formation of the different amino acids.

The genetic codes (DNA codes) for each amino acid have a sequence of three bases. They are known as a triplet (codon).

Examples:  A DNA triplet CAA is the code for the amino acid called valine

 A DNA triplet CGA is the triplet for an amino acid called alanine.

What is non – coding DNA?

 They do not have a code for the formation of a protein.  Non-coding DNA is also known as junk DNA.

4 ©The Dublin School of Grinds Wesley Hammond DNA replication  When mitosis occurs, one cell divides into two identical daughter cells.

 DNA replication occurs so there is an exact copy of the DNA for mitosis to occur.

 Takes place during the interphase of a cell.

How does DNA replication occur?

 The double helix unwinds.  Enzyme breaks the bond between the base pairs.  Other DNA bases now enter the nucleus and join with the exposed DNA strand.  Each new strand is identical to the original strand.

DNA Profiling What is DNA Profiling?  It is a method of making a unique pattern of bands from the DNA of a person which is then used to tell the difference of that DNA from other DNA.

5 ©The Dublin School of Grinds Wesley Hammond Method of DNA profiling?

1) DNA is released 2) DNA is cut into fragments 3) The fragments are separated 4) Patterns are compared

1) DNA is released:  Dna is released by the braking down of the cell.

2) DNA is cut into fragments:  Isolated DNA is cut into fragments using enzymes (restriction enzymes) depending on the sequence of bases.

 The section of DNA bases cut will be of different lengths because of the different distances between the base sequences.

3) The fragments are separated:  Sections of DNA are separated based on their size.  They are separated by a process called gel electrophoresis. An electric current is passed through the gel which allows bands of small DNA fragments to be separated from bands of larger DNA fragments.

NOTE: The smaller DNA fragments move quicker through the gel.

4) Patterns are compared:  If two different DNA samples are the same, then the two samples must have come from the same person.

6 ©The Dublin School of Grinds Wesley Hammond Applications of DNA profiles (DNA fingerprints)

Crime  If a suspects DNA profile is compared to a victims DNA profile in a crime, and they are similar, then it can be said that this person was present at the crime scene.

Medical

 DNA profiles can be used to determine whether a person is the parent of a child (e.g financial inheritance cases)

Genetic screening

 Genetic screening is testing DNA for the presence or absence of a certain gene or an altered gene..

 Genes can be altered by mutations.

 Altered genes do not have the correct code for the production of protein.

NOTE: genetic disorders caused by altered genes include albinism, cystic fibrosis or sickle cell anaemia.

7 ©The Dublin School of Grinds Wesley Hammond Where is genetic screening used?

1) Adult screening:

 Carried out on people who do not have a genetic disorder but may carry altered genes.

 Tells them the chances if their children will have the genetic disease.

Examples: carriers of sickle cell anaemia and cystic fibrosis

2) Foetal screening:

 Cells can be removed from the placenta of a foetus.

 Child can be tested for genetic disorders

What Ethical issues does genetic screening bring?

 Mothers may terminate a pregnancy if they find out their unborn child has a genetic disorder.

8 ©The Dublin School of Grinds Wesley Hammond Detailed look at DNA What is a nucleotide?

• DNA is made up of units called nucleotides.

• A long chain of nucleotides is called a polynucleotides

Structure of a nucleotide:

Sugar is Deoxyribose = D Phosphate group = P Nitrogen base = A or G or T or T

What is a polynucleotide?

 It is many nucleotides joined together.

Structure of a polynucleotide

What holds bases together?  Bases are held together by a hydrogen bond.

9 ©The Dublin School of Grinds Wesley Hammond • Adenine and thymine form two weak hydrogen bonds.

• Guanine and cytosine form three hydrogen bonds.

What are purines and pyrimidines?

There are four nitrogen bases, two are known as purines and two as pyrimidines.

 Two purine bases are (double ringed molecules) : adenine (A) and guanine (G)

 Two pyrimidine bases are (single ringed molecules) : thymine (T) and cytosine (C)

What scientists discovered the shape and structure of DNA?

 Frances Crick and James Watson

Structure of RNA: RNA = ribonucleic acid

• RNA also consist of four bases • RNA contains the base uracil instead of thymine.

What are the four bases: 1) Adenine (A) 2) Uracil (U) 3) Guanine (G) 4) Cytosine (C)

10 ©The Dublin School of Grinds Wesley Hammond Base pairing between DNA and RNA

• RNA is a single stranded molecule.

• The bases in RNA pair up with those in a section of DNA.

Example: If DNA has sequence GCAATC along one strand, then the RNA will have the sequence CGUUAG

Differences between DNA and RNA

11 ©The Dublin School of Grinds Wesley Hammond Protein Synthesis (the making of protein)

• Genes are used to produce different proteins.

• The major steps involved in protein synthesis include:

1) Transcription = making of mRNA from DNA

2) Translation = making of protein depending on the RNA code

Three types of RNA involved in production of protein:

A. messenger RNA (mRNA) B. transfer RNA (tRNA) C. ribosomal RNA (rRNA)

• Remember: all produced in the nucleus!

Steps involved in protein synthesis:

1) Enzymes start to unwind the DNA double helix in the nucleus.

2) Complimentary RNA bases join to the exposed DNA strand (transcription).

3) The enzyme RNA polymerase joins the RNA bases together to form mRNA (messenger RNA)

i) a start codon

ii) a series of codons of different amino acids

iii) a stop codon

5) mRNA moves from the nucleus to the cytoplasm

6) rRNA (ribosomal RNA) are found in the ribosome

7) mRNA then moves into the ribosome and forms a weak bond with the rRNA.

NOTE: ribosome is the site for protein synthesis

8) tRNA (transfer RNA) is found in the cytoplasm.

• tRNA contains an anticodon attached to an amino acid.

9) tRNA is attracted to the mRNA in the ribosome.

10) The anticodon on the tRNA compliments the codon on the mRNA.

11) As the tRNA attach to the mRNA in the ribosome, it also brings with it an amino acid.

13 ©The Dublin School of Grinds Wesley Hammond 12) As the tRNA continue to enter the ribosome, the amino acids detach from the tRNA and bond together to form a new protein.

13) tRNA leave the ribosome without any amino acids and pull with it the mRNA strand out of the ribosome.

14) The process stops once it has reached the stop codon. A new protein has been produced.

______

Solutions 2015, Question 10b:

______

Solutions 2014, Question 10b:

Solutions 2013 Question 6:

Solutions 2011 Question9:

18 ©The Dublin School of Grinds Wesley Hammond Exam Paper 2010 Question 10: Part (a) deals with DNA structure and replication. a) i) Name the base in DNA that pairs with cytosine: ______ii) What are the two main events in the replication of DNA: ______

Part (b) deals with protein synthesis. b) i) Explain the terms transcription and translation: ______ii) In what structures in the cell does translation occur: ______iii) How many bases in sequence make up a codon in mRNA: ______iv) Each mRNA codon specifies one of three possible outcomes during protein synthesis. Name these three possible outcomes: ______v) What does the letter ‘t’ stand for in tRNA: ______vi) During translation one end of a tRNA molecule attaches to an mRNA codon. What is usually attached to the other end of the tRNA molecule: ______

Exam paper 2008 Questions 14b: b) i) DNA is made of units called nucleotides. Draw a labelled diagram of a nucleotide to show its three constituent parts:

ii)Which of the labelled parts in your diagram in (i) may vary from nucleotide to nucleotide: ______iii)The genetic code is contained within the DNA of chromosomes. Briefly describe the nature of this code: ______

20 ©The Dublin School of Grinds Wesley Hammond ______iv)What is meant by non-coding DNA: ______v)Give one structural difference between DNA and RNA: ______vi) Name a cell organelle, apart from the nucleus, in which DNA is found: ______

Solutions 2008 Question 14b:

Exam paper 2004 Question 13

Solutions 2004 Question 13 a, b:

24 ©The Dublin School of Grinds Wesley Hammond 6th Year Biology Higher Level Wesley Hammond is the most recent stellar signing to join Wesley HammondThe Dublin School of Grinds famed teaching team. Wesley takes a revolutionary approach to teaching Biology with his unique student-friendly style of teaching instilling confidence in students by providing them with the skills and techniques required to master the marking scheme and syllabus content. Biology has one of the largest syllabi on the Leaving Certificate and as a result it commands a large amount of students’ studying time, often inappropriate to time spent on other subjects. Wesley is a master at eliminating this serious yet frequently occurring problem, by combining perfectly compiled notes with memorable grinds that aid student’s learning abilities without requiring excessive and inappropriate amounts of studying time.

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