Chapter 3:Nucleotides and Nucleic Acids

What are nucleotides used to make?

Nucleic acids

What are nucleotides made from?

1)A pentose sugar (5 carbon atoms)

2)A nitrogenous (nitrogen-containing base)

3)A phosphate group

What elements make up nucleotides?

C, H, O, N, P

What is the monomer that make up DNA and RNA?

Nucleotides

What is DNA and RNA used for?

1)DNA, stores genetic information- the instructions an organism needs to grow and develop

2)RNA, make proteins from the instruction in DNA

What are the two special types of nucleotides?

ATP and ADP - used to store and transport energy in cells

What is the pentose sugar in DNA called ?

Deoxyribose

What makes up DNA?

1)Each DNA nucleotide has the same sugar and phosphate group

2)There are four possible bases-adenine(A), thymine(T), cytosine(C), guanine(G)

What is a purine base?

A purine base contains two carbon-nitrogen rings joined together

What is a pyrimidine base ?

A pyrimidine base only has one carbon-nitrogen ring, so a pyrimidine base is smaller than a purine base

Adenine and guanine are a type of base called a

Purine

Cytosine and thymine are a type of base called a

Pyrimidine

What does a molecule of DNA contains?

DNA contains two polynucleotide chains-each chain is made up of lots of nucleotides joined together

What is the pentose sugar in RNA called?

Ribose

What makes up RNA?

1)Like DNA, an RNA nucleotide also has a phosphate group and one of four different bases

2)In RNA though, uracil ( a pyrimidine) replaces thymine as a base

What does a molecule of RNA contains?

A single polynucleotide chain.

How do nucleotides join together to form polynucleotides?

1)Nucleotides join up between the phosphate group of one nucleotide and the sugar of another via a condensation reaction

2)The chain of sugars and phosphate is know as the sugar-phosphate backbone

3)Polynucleotides can be broken down by braking the phosphodiester bonds (using hydrolysis reaction)

What bonds are between the bases of DNA?

1)Two hydrogen bonds form between A and T

2)Three hydrogen bonds between C and G

How can DNA self replicate?

in 4 steps

1)DNA helicase breaks the hydrogen bonds between the two polynucleotide DNA strands. The helix unzips to form two single strands.

2)Each original single strand acts as a template for a new strand. Free-floating DNA nucleotides join to the exposed bases on each original template strand by complementary base pairing-A with T and C with G

3)The nucleotides of the new strand are joined together by the enzyme DNA polymerase. This forms the sugar-phosphate backbone. Hydrogen bonds form between the bases on the original and new strand. The strands twist to form a double-helix

4)Each new DNA molecule contains one strand from the original DNA molecule and one new strand

Why is DNA replication called semi-conservative?

1)Because half of the strands in each new DNA molecule are from the original piece of DNA

2)DNA replication is really accurate-to make sure genetic information is conserved each time the DNA in a cell is replicated

What is a mutation and what are their effects?

1)A mutation is any change to the DNA base sequences

2)Mutations don't always have an effect, but they can alter the sequence of amino acids in a protein -this can cause an abnormal protein to be produced

What is a gene?

A gene is a sequence of DNA nucleotides that codes for a polypeptides

How many bases code for one amino acid?

Each amino acid is coded for by a sequence of three bases (called a triplet) in a gene

What is messenger RNA (mRNA)?

1)Made in the nucleus

2)Three adjacent based are called a codon

3)It carried the genetic code from the DNA in the nucleus to the cytoplasm, where it's used to make a protein during translation

What is transfer RNA (tRNA)?

1)Found in the cytoplasm

2)It has an amino acid binding site at one end and a sequence of three bases at the other end called an anticodon

3)It carries the amino acids that are used to make proteins to the ribosomes during translation

What is ribosomal RNA (rRNA)?

1)Forms the two subunits in a ribosome

2)The ribosome moves along the mRNA strand during protein synthesis. The rRNA in the ribosome helps to catalyse the formation of peptide bonds between amino acids

The genetic code is ....

1)Degenerate-there are more possible combinations of triplets than amino acids, this means that some amino acids are coded for by more than one base triplet

2)Universal-the same specific base triplet code for the same amino acid in all living things

What happens during the first stage of protein synthesis ?

During transcription an mRNA copy of a gene is made in the nucleus

What are the nine steps of transcription?

1)Transcription starts when RNA polymerase attaches to the DNA double helix at the beginning of a gene

2)The hydrogen bonds between the two DNA strands in the gene break (helicase) and the DNA molecule uncoils at the point

3)One of the strands is then used as a template to make an mRNA copy

4)The RNA polymerase lines up free RNA nucleotides alongside the template strand. Complementary base pairing expect T is replaced with U

5)Once the RNA nucleotides have paired up with their specific bases on the DNA they're joined together, forming an mRNA molecule

6)The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand

7)The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the stands coil back into a double helix

8)When RNA polymerase reaches a stop codon it stops making mRNA and detaches from the DNA

9)The mRNA moves out of the nucleus through nuclear pores and attaches to the ribosome in the cytoplasm

What happens during translation?

Translation occurs at the ribosomes in the cytoplasm, During this process amino acids are joined together to make a polypeptide chain, following the sequence of codons carried by the mRNA

What are the seven stages of translation?

1)The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome

2)A that's molecule, with an anticodon that's complementary to the start codon the mRNA, attaches itself to the mRNA by complementary base pairing

3)A second tRNA attaches itself to the next codon on the mRNA in the same way

4)rRNA in ribosome catalyses the formation of a peptide bond between the two amino acids attaches to the tRNA molecule. This joins the amino acids together

5)This process continues, process continues producing a chain of linked amino acids until there's a stop codon on the mRNA molecule

6)The polypeptide chain moves away from the ribosome and translation is competed