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DNA Replication

Replace old cells Growth Repair cuts/ wounds Reproduction

Why do cells need to divide?

DNA must replicate, or make an exact copy of itself to put into new cells.

When cells divide, what happens to DNA?

1 DNA 2 DNA

DNA Replication

1: DNA double helix unwinds.

Steps of Replication:

2: Hydrogen bonds break and strands begin to unzip.

Steps of Replication:

3: Free nucleotides pair up with nucleotides on parent strand to form a complementary strand.

Steps of Replication:

At the end of replication, two IDENTICAL daughter strands of DNA have been formed!

What is produced in replication?

Each new strand pairs up with an old strand two produce two DNA molecules each containing one parent (old) and one daughter (new) strand.

DNA replication is semi-conservative

After DNA is replicated, a cell splits to form two cells that each get one copy of the DNA!

What happens to the extra set of DNA?

RNA: ribonucleic acid

Riboonucleic acid

RNA is used to make a temporary copy of the information contained in the DNA of an organism.

What is RNA?

Messenger RNA (mRNA)

Transfer RNA (tRNA)

Ribosomal RNA (rRNA)

Types of RNA

Single helix Single strand Backbone of sugar,

phosphate Nucleotides:

◦ Adenine◦ Guanine◦ Cytosine◦ Uracil

Structure of RNA

DNA is in the nucleus of the cell

BUT

Proteins are made in ribosomes in the cytoplasm

Why do we need RNA?

Instructions from DNA need to be carried to ribosomes so proteins can be made.

Why would it be a bad idea to send the DNA to the ribosomes?

Why do we need RNA?

DNA

Protein Manufacturing

Each cell only has one copy of DNA, so it has to be protected in the nucleus.

Thousands of mRNAs can be made from a DNA template strand, but DNA is only replicated to make a new cell.

DNA is precious!

Transcription

Overview

DNA mRNAtranscription

To make a copy of something

Examples: ◦ Rewriting or typing an

old documents◦ Typing the lyrics to a

song◦ Taking notes from a

PowerPoint!

What does it mean to transcribe?

DNA contains all the information for making the proteins that make up our bodies.

DNA never leaves the nucleus of the cell. If this is true, then how does the rest of the cell get information from the DNA?

DNA Review

1: DNA unwinds

2: DNA unzips

Steps in transcription

3: RNA nucleotides are combined by RNA polymerase to form messenger RNA (mRNA) strand

Steps in transcription

4: DNA rezips and winds back up

Steps in transcription

mRNA leaves the nucleus through a nuclear pore and travels to a ribosome

What happens after transcription?

Proteins are made from the mRNA!

What happens in a ribosome?

How do the instructions work? DNA contains the instructions for making

proteins The instructions are in code The code is based on the sequence of

amino acids—each protein has a particular sequence

Each amino acid has a 3-nucleotide code (like AGA or GCC)

The code is transferred to mRNA

Genetic Code

3 bases of mRNA= 1codon = 1 amino acid

Codon Review

There are 20 amino acids.

The hundreds of thousands of proteins are made with different sequences of amino acids—300 long or more

Amino Acid Review

Each codon is specific to an amino acid.

Genetic Code

One sequence ALWAYS tells a ribosome where to start an amino acid chain.

AUG codes for met (methionine)

Every amino acid chain starts with a methionine in humans.

Start codon- AUG

AUG

Tells a ribosome where to stop reading a strand of mRNA

There are 3 stop codons: UAA, UAG, and UGA.

Stop codons

How to use the genetic code:

What amino acid is coded by:◦ GCU:

◦ GAA:

◦ CUA:

◦ AUU:

◦ UCG:

What amino acid is coded by:◦ UGG:

◦ AUA:

◦ GUC:

◦ GAA:

◦ UUU:

Translation

Overview

mRNA proteintranslation

In a ribosome

Where does translation take place?

Transfer RNA- bring amino acids to ribosome in order to make a protein made of amino acids

mRNA is translated by tRNA

Each 3 base sequence of mRNA is known as a codon and is specific for a particular amino acid.

mRNA Codons

1. tRNA molecule finds and attaches to the specific amino acid it is designed to recognize

Steps to Translation – tRNA attaches to specific amino acid

2: tRNA molecule (with its amino acid) attaches to mRNA codon

Steps to Translation-Attachment

2: A peptide bond is formed between amino acids.

Steps to Translation-Peptide Bond

3: tRNA molecule exits the ribosome. The ribosome shifts down the mRNA.

Steps to Translation-Exit

T: tRNA and amino acid

A: Attachment

P: Peptide Bond

E: Exit

Review of Steps

A chain of amino acids= protein!

What is the end product of Translation?

Protein gets shipped to a part of the cell to do a specific job.

mRNA is broken down into bases that can be used to make new mRNA or translated again to make another protein

What happens after translation?