How does type conversion internally work? What is the memory utilization for the same?

How does Go type conversion internally work?

What is the memory utilisation for a type cast? For example:

var str1 string
str1 = "26MB string data"
byt := []byte(str1)
str2 := string(byt)

whenever I type convert any variable, will it consume more memory?

I am concerned about this because when I try to unmarshall, I get "fatal error: runtime: out of memory"

err = json.Unmarshal([]byte(str1), &obj)

str1 value comes from HTTP response, but read using ioutils.ReadAll, hence it contains the complete response.