0.1 Review - Structrue and Function of DNA

What does DNA stand for

Deoxyribonucleic acid

Where is DNA found and contained

• found in all cells of all organisms

• Mostly contained within the nucleus ( some is contained in the mitochondria)

What does DNA do

• carries instructions for making proteins

DNA replication

• is capable of self replication

What is DNA made up of

• repeating units called nucleotides

What are Nucleotides

• the building blocks of DNA

Nucleotides shape

• the way nucleotides join together into the twisted spiral shape is known as the double helix model

What does a nucleotide consist of

• one 5-carbon sugar

• One phosphate group

• One nitrogen base

How many and what are Nitrogenous bases

• four different nitrogen bases in a DNA molecule

• Cytosine (C)

• Guanine (G)

• Adenine (A)

• Thymine (T)

How are nucleotides linked (DNA) + what type of bond is it

• linked by the phosphate group of one nucleotide bonding covalently with the sugar molecule of the next nucleotide

• This is a strong bond

What are phosphate groups attached to

• phosphate group is attached to the 5’ carbon of one nucleotide and the 3’ carbon of the next nucleotide

What is the DNA ‘backbone’ made of?

• phosphate-sugar-phosphate-sugar-phosphate

• It has a 5’ end and a 3’ end

What direction to the DNA strands run

• one strand runs from 3’ to 5’ and the opposite strand from 5’ to 3’

Middle of the DNA molecule

• known as ‘rungs’

• Paired nitrogen base molecules held together by a hydrogen bond

Bonding of two nucleotides

• forms a base pair

Bonds & what they’re bonded to

• Adenine is slayed bonded with thymine (A-T) and are held together by 2 hydrogen bonds

• Cytosine always bonds with guanine (C-G) and are held together by a 3-hydrogen bond

What type of bonds are hydrogen

• weak bonds

How are DNA stores

• Strands of DNA are looped, coiled and wrapped around proteins called histones.

• In this coiled state, it is called chromatin

• Chromatin is further condensed through a process called supercooling, and it is then packaged into structures called chromosomes

• Each chromosome contains one DNA molecule.

• Human have 23 pairs of chromosomes or 46 chromosomes in total.

Genes

• Chromosomes consists of segments of DNA known as genes

• Genes contain instructions for the construction of a particular protein

• Different genes are activated in different cells ie genes for insulin production are activated in the pancreas but not in bones or muscles n

The function of DNA - the genetic code

• to provide the instructions for protein synthesis

• Proteins can have many functions such as:

  • control all chemical reactions (enzymes)

  • Provide structure in bone cartilage and skin

  • Control the movement across plasma membrane

  • Provide contractile elements in muscle cells (actin and myosin)

  • Hormone messengers

What are proteins made up of

• a long chain of amino acids folded into a 3D shape

Sequence of amino acids

• defined by a gene

• The sequence is a code instructing the cell how to construct a particular protein

Reading the code

• the sequence of bases is read in groups of three, called codons

• Each codon represents one of the 20 different amino acids

Protein synthesis

the assembly of amino acids to construct a protein involves the processes of:

• Transcription

• Translation

Transcription definition

• the process by which a genes DNA sequence is copied into messenger RNA (mRNA)

3 steps of transcription

1. Initiation

2. Elongation

3. Termination

Initiation

• the beginning of transcription

• Occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter

• This signals the DNA to unwind so the enzyme can “read” the bases in one of the DNA strands.

• The enzyme is ready to make a strand of mRNA with a component army sequence of bases

Elongation

• is the addition of nucleotides to the mRNA strand

Termination

• the ending of transcription

Translation definition

• the process in which the genetic code carried by mRNA directs ribosomes to connect amino acids together to produce proteins.

Steps of translation

• A ribosome attaches to one end of the mRNA molecule at a particular sequence of bases that is the 'binding site' for the ribosome.

• The ribosome then moves along the mRNA three bases at a time reading the code of bases.

Transfer RNA purpose

• tRNA brings individual amino acids to the

  ribosomes to be joined together.

Order of amino acids - tRNA

• The specific order that individual amino acids are joined to one another is determined by the sequence of the codons in the mRNA.

tRNA structure

• the loop of the tRNA has 3 nitrogen bases that form an anticodon

• These 3 bases bind with the complementary bases of a codon on the mRNA molecule

After the tRNA has delivered its amino acid

• it detaches from the ribosome and can pick up another amino acid from the cytoplasm

Ribosomal RNA (rRNA)

• found in the ribosomes

• Assists in the creation of the peptide bonds between the amino acids

When does DNA replication occur

• during the S-phase (synthesis) of the cell cycle

DNA replication

• produces two copies of the original DNA molecules

• Copies are identical and original to each other

• Each new molecule has one original strand and one new strand (DNA replication considered semi-conservative)

• Ensures cells produces by mitosis are genetically identical to each other and to original cell

One chromosome DNA replication

= one long DNA molecules

• this is how chromosomes are duplicated prior to mitosis